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  • Water and nutrient retention in coarse-textured soil profiles from the Athabasca oil sand region
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-11
    Frédéric Rees; Sylvie Quideau; Miles Dyck; Guillermo Hernandez; Marty Yarmuch

    Post-mining land reclamation of Athabasca Oil Sands (AB, Canada) involves the reconstruction of soil profiles able to support a mosaic of boreal forest communities. However, the use of coarse-textured reclamation materials to recreate forest ecosystems represents a challenge in terms of soil water and nutrient availability. This work aimed to quantify nutrient leaching in reclaimed coarse-textured soils constructed with two coversoils (peat mineral mix and forest floor mineral mix) underlain by mineral materials, including a blended B/C subsoil reclamation material, lean oil sand overburden substrate, and tailing sand. Water retention and conductivity curves were estimated for each material, and their retention capacity for inorganic N and P was measured in sorption isotherm experiments. The redistribution of water, inorganic N and P five days after an intense rain event was evaluated in six different reclaimed soil profiles using a laboratory-controlled leaching experiment in 1.2-m deep columns. The redistribution of fertilizer nutrients was also measured following the addition of 15N-labelled ammonium and phosphate over the top 10 cm of the columns. In addition, a 25-day incubation experiment with the two coversoils enabled us to estimate the timing of N immobilization and nitrification processes. Our results show that, depending on the combination of materials used for land reclamation, the soil profiles may provide equal or higher amounts of inorganic N and P in the rooting zone compared to natural, coarse-textured soils of the region. Following the simulated intense rainfall, the peat-mineral mix was able to retain 44% of its initial inorganic N within the top 20 cm of the reclaimed soil profiles, while 84% of the inorganic N present in the forest floor mineral mix was leached down. Compared to the movement of water, the leaching of N down the soil profiles was slower and partly restricted by the presence of lean oil sand, and to a lesser degree tailing sand. Most of the introduced fertilizer-N remained in the first 20 cm of the soil profiles under the form of nitrate, although the incubation experiment suggested that nitrification only occurred after the simulated rainfall event. Based on our experimental data and on additional simulations of water and nutrient transport, we conclude that nutrient leaching in reclaimed soils can be significant if specific materials such as forest floor mineral material and coarse-textured subsoil are combined and when an intense rainfall occurs at a period coinciding with a high concentration of nitrate-N in the topsoil.

    更新日期:2020-01-13
  • Water-soluble bitumen degradation products can fuel nitrate reduction from non-radioactive bituminized waste
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-11
    Kristel Mijnendonckx; Axel Van Gompel; Ilse Coninx; Nele Bleyen; Natalie Leys

    An important fraction of the currently stored volume of long-lived intermediate level radioactive waste in Belgium is immobilized as Eurobitum. This type of waste typically contains large amounts of NaNO3 homogeneously dispersed in a hard bituminous matrix. Geological disposal of Eurobitum in a water-saturated sedimentary formation such as Boom Clay will result in the leaching of high concentrations of NaNO3 in the Boom Clay formation. This could cause a geochemical perturbation of the surrounding clay, possibly affecting some of the favorable characteristics of the host formation such as its hydraulic conductivity, sorption potential or the redox conditions. The latter might result in a decrease of its reducing capacity and an increase in the mobility of redox-sensitive radionuclides. Microbial nitrate reduction is a well-known process, which could be stimulated by the chemical and radiolytical water-soluble organic bitumen degradation products. The present study carried out different series of long-term anoxic batch experiments to investigate the ability of the microbial community of Boom Clay borehole water to reduce nitrate, leaching from thermally aged non-radioactive Eurobitum in the presence or absence of acetate, formate and oxalate, being the most important organic bitumen degradation products. Obtained results indicate that all three organic bitumen degradation products can be used as electron donor to fuel microbial nitrate reduction, albeit with a different efficiency. The highest nitrate reduction rate was observed in the presence of acetate, while oxalate was the least efficient electron donor for nitrate reduction. Moreover, organic compounds that leached from the Eurobitum during the course of the experiment were used as electron donor for microbial nitrate reduction in all conditions. Furthermore, calcium oxalate crystals were observed, indicating that if oxalate is present, it will probably be less bioavailable compared to other organic compounds.

    更新日期:2020-01-13
  • Hydrochemical evolution of groundwater in gabbro of the Troodos Fractured Aquifer. A comprehensive approach
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-11
    Christos Christofi; Adriana Bruggeman; Christoph Kuells; Costas Constantinou

    Ophiolites often form complex, fractured, multi-lithological and highly compartmentalized aquifers that are difficult to characterize. Groundwater chemistry reflects water-rock interactions and can provide insights to groundwater recharge mechanisms, flow paths and relative residence time. A comprehensive hydrogeochemical modelling approach with PHREEQC has been developed to identify water-rock interactions and simulate groundwater evolution and mixing with connate water in fractured aquifers. The methodology was applied in the gabbro aquifers of Troodos Massif (Cyprus). The geochemical processes generating the most frequently observed water types were reproduced through modelling. Based on the overall results, a generic evolution path has been identified: CaMgHCO3 → MgCaHCO3 → CaMgNaHCO3 → Ca/Mg/Na/HCO3/SO4 → NaMgHCO3SO4 → NaSO4/Cl group. CaMgHCO3 and MgCaHCO3 types were modelled to occur predominantly in early stages of recharge. Deep unsaturated zones and longer flow paths result in gradual removal of Ca+2 and Mg+2 from groundwater, through secondary mineral precipitation, and in an increase of Na+2 and SO4−2. The most frequently occurring water types, CaMgNaHCO3 and MgCaNaHCO3, were modelled to occur at later stages of hydro-chemical evolution, after secondary mineral precipitation, and in closed conditions. In regional flow, where closed conditions with secondary mineral precipitation prevail, water types progressively shift from the HCO3 to the NaSO4 end-member group. In 38% of the 536 samples from gabbro aquifers in Troodos, groundwater mixing with connate water at a ratio of ≥0.999:0.001 occurs.

    更新日期:2020-01-13
  • Identification of gas inflow zones in the COSC-1 borehole (Jämtland, central Sweden) by drilling mud gas monitoring, downhole geophysical logging and drill core analysis
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-08
    Thomas Wiersberg; Simona Pierdominici; Henning Lorenz; Bjarne Almqvist; Iwona Klonowska

    On-line monitoring of drilling mud gas was for the first time applied during continuous wireline coring of the COSC-1 borehole (Jämtland, central Sweden) to analyse formation gases and to identify inflow gas zones. Nearly complete gas records were obtained with three meter depth resolution from 662 m (installation of the separator for gas extraction) to 1709 m and six meter resolution from 1709 m to 2490 m depth (COSC-1 final depth: 2498 m) for H2, CH4, CO2, and He. Between 662 m and 1400 m, both He and CH4 form broad peaks superimposed by several spike-like features. Zones with gas spikes coincide with high resistivity intervals from dual laterolog (DLL) geophysical borehole logging and show fractures in borehole televiewer (BHTV) images, drill core scans, and visual core inspection. Therefore, we assume gas inflow through open fractures where DLLd/DLLs ratios >1.5 imply the presence of free gas. The correlation between helium and DLLd/DLLs ratios no longer appears at depths greater than ∼1500 m, probably because the formation gases are dissolved in formation fluids at higher pressure. Below 1550 m depth, He drops significantly, whereas CH4 remains relatively high and H2 and CO2 reach maximum values. The high amount of hydrogen and methane at depths below 1616 m, from where friction between the casing and the drill string was reported, imply that these gases are most certainly artificially generated at depths below 1616 m and at least partly of artificial origin at shallower depths.

    更新日期:2020-01-08
  • A new carbonate-specific quantification procedure for determining elemental concentrations from portable energy-dispersive X-ray fluorescence (PXRF) data
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-12
    Mohammed Al-Musawi; Stephen Kaczmarek

    Portable energy-dispersive X-ray fluorescence (PXRF) analyzers are routinely used to generate large elemental datasets in sedimentary strata. These data provide the basis for assessing stratigraphic changes in geochemistry, bulk mineralogy, and paleo-redox conditions. The manufacturer provided procedure used to calculate elemental concentrations from PXRF photon counts that was developed for siliciclastic mudrocks. This quantification is, however, routinely applied to other sedimentary rocks, such as carbonates, which often have very different elemental concentrations and rock textures. The current study reports elemental concentration data from 57 limestone and dolomite rock samples measured by both PXRF and conventional geochemical analyses including inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma - optical emission spectrometry (ICP-OES), and wavelength-dispersive X-ray fluorescence (WD-XRF). Carbonate samples were subdivided into two groups. The calibration set (N = 43) is used to establish a carbonate-specific PXRF quantification procedure, and to investigate the effects of different sample preparation techniques. The validation set (N = 14) is used to evaluate the applicability of both the newly developed carbonate-specific quantification procedure and the existing mudrock quantification procedure for the carbonate rock suite. PXRF measured photon counts in the calibration set exhibit strong positive linear correlations (R2 = 1–0.76) with the elemental concentrations independently measured from ICP-MS and/or ICP-OES, and WD-XRF. These linear relationships were used to calculate elemental concentrations in the validation set, which were then statistically compared with the measured elemental concentrations. Results of the carbonate-specific quantification procedure show that 13 elements (Mg, Al, Si, P, K, Ca, Ti, Mn, Fe, Rb, Sr, Y, and Zr) in the carbonate validation set are quantified with PXRF at the definitive data quality level. The mudrock-based quantification procedure, in contrast, quantified only 4 elements at the definite data quality level (Si, K, Ca, and Zr), suggesting that carbonate-specific calibration should be used to ensure higher data quality. The results from the sample preparation experiments exhibit different linear regressions for whole rock, loose powders, pressed powder pellets, and fused discs. The results of this study show that (i) PXRF can reliably identify and accurately quantify the concentrations of 13 common rock-forming elements in carbonate rocks; (ii) the carbonate-specific quantification procedure provides a higher level of data quality for carbonate rocks compared to the mudrock-based quantification; (iii) carbonate rock samples are inherently heterogeneous and thus require more intensive sample preparation and advanced statistical methods to account for this in the quantification procedure; and (iv) the matrix effect that results from different sample preparations must be accounted for in the quantification procedure.

    更新日期:2020-01-04
  • Geothermometry and geochemistry of groundwater in the Continental Intercalaire aquifer, southeastern Algeria: Insights from cations, silica and SO4–H2O isotope geothermometers
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-12
    Adel Abdelali; Imed Eddine Nezli; Rabah Kechiched; Said Attalah; Slimane Abdeldjabbar Benhamida; Zhonghe Pang

    Characterization of geochemistry and geothermometry of the groundwater from the Continental Intercalaire (CI) aquifer, one of the largest aquifers in the world, stretching over one million km2 surface area shared between Algeria, Tunisia and Libya, was conducted in southeastern Algeria nearby the border with Tunisia. Thirty-two water samples were collected from boreholes to analyze the physicochemical parameters and stable isotopes (δ18O(H2O), δ18O(SO4), δ 34S(SO4)) and determine the origin of water mineralization of the CI aquifer. Water temperature was assessed using several geothermometers, such as cations, silica and SO4–H2O stable isotopes. The CI aquifer displayed a discharge temperature varying from 45 to 65.1 °C due to water circulation at deeper depths ranging from 1000 to 2200 m. The Results show that CI water contains high total dissolved solids (TDS) and neutral to slightly alkaline pH. The most frequent water types were Na–Cl–SO4 and Ca–SO4 indicating the geological formation nature of CI aquifer which is mainly composed of evaporites. The application of Na–K and Na–K–Ca geothermometers yielded unreliable temperatures. However, Na–Li geothermometer resulted in relatively plausible temperatures ranging from 74.69 to 147.83 °C. Quartz and CaSO4–H2O isotope geothermometer are the most suitable methods for temperature estimation, due to their attainment of equilibrium resulting in temperatures ranging from 62 to 93 °C, and validation by the multiple mineral equilibrium approach. The present study demonstrated a successful application of CaSO4–H2O isotope geothermometer in a low enthalpy (<100 °C) geothermal system. The results corroborate previous findings on the same CI aquifer at the Tunisian side and on carbonate-evaporite geothermal reservoirs. Furthermore, geothermal potential of the CI aquifer has been highlighted suggesting its use as a source of renewable energy which could be applied in heating greenhouses and/or generating electricity.

    更新日期:2020-01-04
  • Elevated dissolved heavy metal discharge following rainfall downstream of intensive horticulture
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-13
    Stephen R. Conrad; Isaac R. Santos; Shane A. White; Samantha Hessey; Christian J. Sanders

    Heavy metals may be released from soils during rain events. Observations during the first flush (rain event preceded by dry period) are difficult, but may account for a large fraction of annual loads. Here, we report detailed time series measurements of dissolved heavy metals and the groundwater tracer radon (222Rn) over multiple rain events from a creek draining a catchment dominated by intensive horticulture on the subtropical east coast of Australia. The creek drains to an intermittently closed and open lake or lagoon (ICOLL), a typical estuary type along the east coast of Australia. A sandbank prevents the estuary mouth from connecting with the ocean during dry conditions. Following a 109 mm rain event, the ICOLL began to drain to the coastal ocean. Mean export of Hg, Cu, and Zn was 0.23 ± 0.05, 1.06 ± 0.25, and 15.70 ± 2.69 g m−2 day−1 for the entire time series and 0.72 ± 0.17, 1.27 ± 0.12, 24.14 ± 3.82 g m−2 day−1 averaged from high resolution sampling over 72 h of the first flush event. Trends of Hg export differed from the other heavy metals. Over 79% of the estimated Hg export occurred within 72 h of the ICOLL opening, compared to 30 and 38% of Cu and Zn. The first flush and subsequent major rain events (> 50 mm day-1) drove concentrations of Hg, Cu and Zn to exceed the Australia and New Zealand Environment and Conservation Council (ANZECC) water quality guidelines (WQG) for both fresh and marine water. Comparisons of heavy metal export to downstream estuary sediment burial rates revealed that the estuary is likely a source of dissolved Hg and Cd to the coastal ocean when the ICOLL is open.

    更新日期:2020-01-04
  • Geogenic groundwater arsenic in high altitude bedrock aquifers of upper Indus river basin (UIRB), Ladakh
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-16
    Suhail A. Lone; G. Jeelani; Abhijit Mukherjee; Poulomee Coomar

    Many sedimentary aquifers across the globe are contaminated with As, a known toxicant and carcinogen, thereby making millions of people vulnerable to a health hazard. Although the source of As enrichment is being linked to the provenance of the sediments (i.e. hard rocks), there are limited studies of groundwater As enrichment in hard rock areas. In this study, we collected the groundwater samples from complex hard rock aquifer system across the Himalayan collision zone in Upper Indus River Basin (UIRB) to understand the source and to evaluate the hydrogeochemical processes responsible for groundwater As mobilization. The study suggests that groundwater As enrichment comes from volcanic rocks and ophiolitic mélange. Such, As contaminated aquifers are widely used for groundwater exploitation for drinking and other purposes in Ladakh (UIRB). The results indicated that As enrichment occurs with an increase in temperature and depth. The results also indicated that the groundwater in Ladakh is described by multiple hydrochemical facies with pH circum-neutral to alkaline in nature. Higher pH, Fe2+ and Mn and lower ORP, NO3−, and SO42− in groundwater are found to be associated with high As groundwater indicating metal oxides/hydroxides under reducing conditions are predominantly controlling the groundwater As mobilization.

    更新日期:2020-01-04
  • Surface interaction of crude oil, maltenes, and asphaltenes with calcite: An atomic force microscopy perspective of incipient wettability change
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-13
    Maria C. Marcano; Sooyeon Kim; Udo Becker

    Close examination of surface interactions between calcite and crude oil is relevant to better understand the mechanisms that lead to wettability changes in petroleum reservoirs. Mineral surface wettability is a determinant factor in petroleum production and recovery, and the surface-active compounds in crude oil, typically concentrated in its asphaltene fraction, are mainly responsible for these wettability changes. Here, we use atomic force microscopy (AFM) to examine the incipient interactions between calcite {101‾4} surfaces and the Kuwait UG8 crude oil, and its asphaltene and maltene (i.e., crude oil after asphaltene has been extracted) fractions. The resulting adsorbates are interpreted on the basis of coverage, size, shape, and distribution. Adsorbates from crude oil are equally-spaced hemispheroidal droplets occurring predominantly at [4‾41] and [481‾] surface steps with a separation of about 550 nm between centers of adjacent adsorbates. Adsorbates from asphaltenes are irregularly spaced droplets or continuously cover the steps along the edges of dissolution pits. The average and standard deviation of diameter and height of 10–16 representative adsorbates from the selected images highlight the contrast among samples. Crude oil adsorbates average about (240 ± 120) nm in diameter and (60 ± 30) nm in height. Diameters of isolated adsorbates and lateral dimension of elongated adsorbates of asphaltene average (100 ± 20) nm and (150 ± 40) nm, respectively, and about (30 ± 10) nm in height overall. Isolated non-periodic smaller adsorbates (average diameter (20 ± 5) nm and height (7 ± 3) nm) occur from the maltene fraction and are mostly restricted to steps surrounding dissolution pits. Adsorbates from maltenes are most likely produced by resins that remain in this fraction after extracting the asphaltenes. Adsorption from crude oil involves the greatest surface area compared to asphaltenes and maltenes. Based on the sizes and heights of adsorbates reported here, we infer that, unlike resins, asphaltenes in crude oils act as anchors for increased oil adsorption and help enhance the change of an original water-wet surface to an oil-wet one. Differences in average height and architecture between adsorbates from oil and asphaltenes (i.e., isolated vs. continuous) may in part be associated to increased aggregation in toluene, which will intensify colloidal interactions before adsorption. We argue that asphaltenes in crude oil help stabilize larger, almost periodically spaced adsorbates all throughout the calcite surface and not only along the deeper steps that border large dissolution pits. The computational model of a chosen specific asphaltene molecule attached to a calcite surface shows strong interactions between hydroxyl groups and Ca2+ cations on the calcite surface in addition to weaker interactions of the negatively charged π orbitals of the polycyclic aromatic hydrocarbon (PAH) center and the surface cations, which is in agreement with the notion of establishing asphaltene anchors on calcite. Along with basic chemical information, systematic AFM imaging of a variety of crudes may become part of a practical strategy to evaluate surface-active compounds in oil and to predict their likely molecular structure and participating functional groups.

    更新日期:2020-01-04
  • Sorption of rare earth elements on schwertmannite and their mobility in acid mine drainage treatments
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-14
    Alba Lozano; Carlos Ayora; Alejandro Fernández-Martínez

    Rare Earth Elements (REE) are nowadays considered critical raw materials due to their increasing use in modern industry and their shortage of supply. Acid mine drainage (AMD) contains REE concentrations several orders of magnitude higher than the rest of continental and marine waters, and the sludge from its treatment may become a supplementary source of REE. Schwertmannite, a Fe(III)-sulfate-hydroxide is the most common mineral precipitated from AMD and a main constituent of the neutralization sludge. The objective of this work is to study the mechanism of REE retention in synthetic schwertmannite and to predict the REE behavior in a column experiment mimicking an AMD passive remediation system. Suspensions of synthetic schwertmannite in sulfate solutions show that Y and the lanthanides are effectively sorbed at pH values higher than 4.5, and sorption is complete at pH values higher than 6.5. The experimental partition coefficients clearly show a preferential enrichment of heavy REE in the solid phase. Unlike the rest of the REE, Sc sorption occurred at a lower pH, from 3 to 5. The experimental results have been described with a non-electrostatic surface complexation model in which the aqueous complex MSO4+ exchanges with two H+ from the surface of schwertmannite, forming a bidentate surface complex, (XO)2MSO4-. Scandium sorption was also accurately predicted with the addition of a second bidentate surface complex, (XO)2MOH. The equilibrium constants for REE sorption on schwertmannite calculated in the present work, together with those for REE sorption on basaluminite (Lozano et al., 2019, GCA, 258, 50–62) were used to model the behavior of different REE observed in the pore water and solid of a column experiment. Schwertmannite and basaluminite were the main solid phases formed due to the progression of the neutralization. First schwertmannite precipitated at pH below 4 and then basaluminite precipitated at pH above 4. Both minerals can sorb REE in a similar pH range. However, since Y and the lanthanides sorbed at pH values higher than 5, their sorption only occurred on basaluminite. In contrast, the Sc sorption edge extended from pH 3 to 5 and Sc partially sorbed on schwertmannite. As a practical consequence, REE preferentially accumulated in the basaluminite residue of AMD neutralization systems, but a minor fraction of Sc can be retained in the schwertmannite waste.

    更新日期:2020-01-04
  • Dissolution evaluation of coquina part 2: Alternating carbonated brine and equilibrated brine injection using computed tomography and PHREEQC
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-17
    Janeth Alina Vidal Vargas; Eric Yuji Yasuda; Erika Tomie Koroishi; Osvair Vidal Trevisan

    Geochemical modeling of CO2-water-rock chemical interactions plays a crucial role in enhanced oil recovery (EOR) processes and CO2 storage. This work develops a geochemical model and an injection sequence that alternates carbonated brine (CB) and equilibrated brine (EB). The model was fitted using the PHREEQC geochemical simulator and two sets of experimental data: (1) calcium and magnesium concentration from the effluents and (2) the amount of calcite dissolved from computerized tomography (CT) measurements. The model incorporates the overall assessment of the calcite kinetics theory and surface complexation. Chemical interactions on the mineral surface promote mineral dissolution and precipitation, which can lead to changes of permeability, porosity, and integrity of reservoir. To understand and simulate the chemical interaction between rock and the injection fluid, this work tested different flow rates (0.025, 0.075, 0.1, and 2 ml/min at 13.789 MPa and 20 °C) alternating the injection sequence of CB and EB. Permeability and porosity were evaluated using pressure measurements and CT, respectively. The Péclet (Pe) and Damköhler (Da) numbers were determined for each flow rate and the dissolution regime was characterized. We developed a geochemical model using the PHREEQC taking into account the theory of calcite kinetics and complexation surface to predict the behavior of mineral dissolution during reactive transport using CT (computed tomography) and effluent analysis. The novelty of alternating the injection sequence of CB and EB provided the chemical interaction between the coquina and the fluids, promoting dissolution of minerals, and thus altering permeability and porosity. Calculating Da and the reaction rate along the porous medium facilitated the evaluation and quantification of the different patterns of calcite dissolution, which were due to the flow rate variation and the alternate injection of water. Analysis showed that low flow rates promote greater dissolution at the beginning of the sample, high flow rates promote dissolution throughout the sample, and the sample heterogeneity also influences dissolution. Finally, we used surface complexation to correctly represent the effects of interactions between CB/EB and the coquina, as these interactions affect the quantity of magnesium production.

    更新日期:2020-01-04
  • Experimental study of shale-fluids interaction during oxidative dissolution with hydrogen peroxide, sodium hypochlorite and sodium persulfate
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-17
    Yilian Li; Sen Yang; Danqing Liu; Cong Yang; Zhe Yang; Hai Li; Zhi Tang

    The drastic decline of shale gas production after fracturing depresses the development of this unconventional gas resource. Although shale oxidant stimulation can dissolve unstable composition to enhance permeability, the shale-fluids interaction during this stimulation process is still not yet clear. In this study, the organic-rich shale collected from the Cambrian Shuijingtuo Formation of Yichang, Hubei province, China was selected to react with three oxidants, hydrogen peroxide (H2O2), sodium hypochlorite (NaClO) and sodium persulfate (Na2S2O8) at formation temperature. Variation of water chemistry, mineral composition and micromorphology were analyzed to reveal the mechanism of shale oxidative dissolution and evaluate its influence on shale permeability enhancement. Results showed that pyrite and OM can be discrepantly oxidized with different oxidants. At the same oxidation duration, the acidic environment was beneficial for carbonate dissolution, while the alkaline environment was favorable to the dissolution of dolomite and tectosilicate minerals such as quartz, albite, illite and chlorite. Nevertheless, the serious thermal decomposition of H2O2, precipitation of gypsum and ferric hydroxide (Fe(OH)3) occurred during shale-fluids interaction at formation temperature might impede the enhancement of shale permeability. The oxidative dissolution of shale also brought about the release of trace elements, which might result in groundwater pollution. For the in-situ application of shale oxidative dissolution, difficulties such as thermal decomposition, secondary minerals precipitation and possible groundwater pollution should be considered further in the future.

    更新日期:2020-01-04
  • 更新日期:2020-01-04
  • Bioprecipitation of As4S4 polymorphs in an abandoned mine adit
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-23
    Lukáš Falteisek; Petr Drahota; Adam Culka; František Laufek; Jakub Trubač
    更新日期:2020-01-04
  • Selenium mass balance and flux in water of Pariette Wetlands, Utah (USA)
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-26
    Colleen P. Jones; Michael C. Amacher; Paul R. Grossl; Astrid R. Jacobson

    Selenium (Se) has potentially deleterious impacts on flora and fauna of aquatic ecosystems. As Se moves through a wetlands system, various processes such as sorption onto sediments, plant uptake, and volatilization into the atmosphere can attenuate Se resulting in its storage in the wetlands. A comparison of inlet and outlet Se fluxes can be used to determine the mass of Se stored in a wetlands system. Inlet and outlet total Se concentrations and water discharge were measured at the Pariette Wetlands, UT, and used to calculate Se fluxes. The difference between inputs and outputs or fluxes gave great insight into how much Se was being retained or stored in the wetlands. The average influx of Se was 1530 kg year−1 and outflux was 380 kg year−1. On average, 75% (1150 kg year−1) of Se entering the wetlands was retained or stored by some biogeochemical process. Processes associated with Se retention included bioaccumulation into the biota, volatilization by plants and sediments, precipitation of insoluble phases, and sorption to sediments, which accounted for most of the attenuated Se. Water movement through the Pariette Wetlands system did not appreciably alter annual Se attenuation rates. Input, output, storage, and fate of Se for four other wetlands were compared with Pariette Wetlands with Se storage being similar among three of the wetlands: Tulare Lake (65%), Imperial (46%), Brawley (72%), and Pariette (75%).

    更新日期:2020-01-04
  • Degradation and pollution of lands under the influence of oil resources exploitation
    Appl. Geochem. (IF 2.894) Pub Date : 2019-10-18
    Sergei A. Buzmakov; Yuliya V. Khotyanovskaya

    The research considers the degradation and pollution of soils as a result of oil extraction activities. The object of the research includes the territories of the exploited oil fields located in the Sarmatic mixed forests in Perm region. A total survey of the Gozhanskoye field was carried out, which revealed that the most dangerous processes of transformation and accumulation of pollutants are concentrated in the zone of influence of the primary oil treatment units (rus. UPPN, see the map). The other seven areas of the UPPNs were also surveyed. In total, 303 soil samples were taken as part of the study. The analysis determined such characteristics of oil samples as acidity, the content of humus, hydrocarbons, benzo[a]pyrene and chlorides. Measurements of oil content in the soil were carried out by the IR-spectrometry method. Benzo[a]pyrene was extracted from soil following the standard procedure and analyzed through gas chromatography testing. The physico-chemical analysis allowed to find out the concentrations of the main pollutants, as well as to design maps of land degradation and pollution. Another important finding is that the oil fields exploitation has the most essential impact on primary degradation of floodplain and upland soils as a result of salinization and benzo[a]pyrene pollution.

    更新日期:2020-01-04
  • Methodological aspects in the analysis of the content of mobile compounds of heavy metals in hydromorphic soils
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-12
    Yuriy Vodyanitskii; Tatiana Minkina; Inna Zamulina

    The content of mobile compounds of Zn, Pb and Cu in the hydromorphic soil samples with natural humidity from southern European Russia turned out to be much higher than in samples stored in laboratory for 1 month and, particularly, 3 years. At the same time, the extractability of heavy metals is characterized by irregular kinetics: their solubility decreases rapidly during the first month when the dry soil sample loses the initial humidity, but slowly during its further storage for 3 years. Solubility of metals in natural humid soils is highly variable. Influence of the studied reagents (CH3COONH4, EDTA and oxalate) shows the following general trend: Zn > Pb ≫ Cu. Solubility difference of metals is smoothed over in the course of soil drying. In terms of the dissolution efficiency of mobile metal compounds in the hydromorphic ferruginated soils, the extractants are arranged in the following order: oxalate > EDTA > CH3COONH4. Since the oxalate actively dissolves Fe(II)-compounds in soils, the solubility of metal is governed by the its siderophility. Zn is most intensely dissolved by oxalate, while Pb and Cu in soils demonstrate organophilic properties. However, Pb can also be sorbed on iron hydroxide particles.

    更新日期:2020-01-04
  • Understanding cementitious backfill interactions with groundwater components
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-13
    Timothy Heath; James Schofield; Amy Shelton

    Many concepts for the disposal of intermediate-level radioactive waste specify the emplacement of waste packages in underground vaults backfilled with cementitious material. The cementitious backfill performs a number of functions including maintaining alkaline conditions and providing a high sorption capacity for radionuclides. In the UK, the Nirex Reference Vault Backfill (NRVB) has been developed for such a role. To improve our understanding of its long-term performance, a detailed programme was undertaken to investigate interactions of the NRVB with selected groundwater components using sodium sulphate and magnesium chloride solutions. Experiments using the selected solutions were performed under conditions of constant flow, over timescales of up to 860 days. Elemental composition and pH of the egressing eluent were determined throughout the experiments. At the end of the experiments, detailed solid analyses were performed on samples from various locations in the NRVB using a wide range of techniques. In the sodium sulphate experiment, sulphate attack resulted in the formation of ettringite, thaumasite and gypsum. For the magnesium chloride case, the results were dependent on the concentration of the magnesium in the ingressing solution. At higher concentration, precipitation of brucite at the upstream surface of the NRVB led to clogging and termination of the experiment after about one month. At lower concentration, no such clogging occurred, despite almost all the ingressing magnesium being removed by the NRVB over timescales of more than two years. For both systems, high pH values of the eluent were maintained over the full periods studied; for the sodium sulphate experiment the final pH was 12.7 (after 180 sample volumes) and for the low concentration magnesium chloride case pH 11.5 (after 749 sample volumes). A “top-down” modelling approach was applied to interpret the results, involving solution equilibration with the NRVB represented by a simple set of mineral phases. Further processes were modelled only where they improved the overall fits. The resulting models were considered to be simple while maintaining consistency with the major features of the experimental data sets. This has helped to provide mechanistic interpretations of the evolution of NRVB, based on relatively simple sets of secondary mineral phases, early kinetic control of mineral dissolution and diffusion-restricted release of portlandite at longer times.

    更新日期:2020-01-04
  • Stabilization of soils containing sulfates by using alternative hydraulic binders
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-21
    Laura Diaz Caselles; Julie Hot; Cédric Roosz; Martin Cyr

    Excavation operations during construction produce several tons of soil, which frequently contain high concentrations of sulfates (>0.5 wt%). In accordance with the requirements of the French decree for waste classification for disposal, a soil containing sulfates is classified as “inert and non-hazardous waste” if the leachable sulfate concentration is lower than a mass fraction of 0.1%. To prevent sulfate leaching from excavated soils, solutions for immobilizing sulfates are needed and the associated stabilization mechanisms must be understood. On the other hand, the reuse of soils containing sulfates for civil engineering purposes can lead to significant risks after their treatment with ordinary cementitious binders because of chemical reactions involving sulfates. These reactions can promote the formation of massive ettringite crystals resulting in expansion, cracking and eventually catastrophic damage of materials or structures. For these reasons, the stabilization of soils containing sulfates by adding alternative hydraulic binders is studied in this paper. Several binders were used to treat a sulfate-spiked soil. It was observed that treatment with cementitious binders having high C3A content led to volume expansions greater than 5%, while treatments with binders containing a high fraction of ground granulated blast furnace slag (GGBS) showed volume expansions of less than 5% and about 89% of sulfates were immobilized in the solid matrices. These preliminary results suggest that GGBS binders are effective for the treatment of soils containing sulfates. Moreover, numerical calculations using PHREEQC were compared with experimental results to improve the understanding of sulfate immobilization mechanisms.

    更新日期:2020-01-04
  • Formation and prevention of pipe scale from acid mine drainage at iron Mountain and Leviathan Mines, California, USA
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-03
    Kate M. Campbell; Charles N. Alpers; D. Kirk Nordstrom

    Pipelines carrying acid mine drainage (AMD) to treatment plants commonly form pipe scale, an Fe(III)-rich precipitate that forms inside the pipelines and requires periodic and costly cleanout and maintenance. Pipelines at Iron Mountain Mine (IMM) and Leviathan Mine (LM) in California carry acidic water from mine sources to a treatment plant and have developed pipe scale. Samples of scale and AMD were collected from both mine sites for mineralogical, microbiological, and chemical analysis. The scale mineralogy was primarily schwertmannite with minor amounts of poorly crystalline goethite. Although the bulk composition of the scale was similar along the length of the pipeline at IMM, the number of iron-oxidizing bacteria and concentrations of associated trace elements decreased along the flow path inside the pipeline. Laboratory batch experiments with unfiltered AMD from IMM and LM showed that Fe(II) oxidation was driven by microbial activity when the pH was <5. A remediation strategy of decreasing the pH to <2.2 was tested through geochemical modeling and laboratory experiments. These experiments indicated that scale formation could be prevented by decreasing the pH, which could be achieved at IMM by mixing source waters. However, the presence of Fe(III)-rich scale in a pipeline buffers the pH to higher values that may affect the efficacy of this remedial approach.

    更新日期:2020-01-04
  • Hydrogeological controls of arsenic and uranium dissolution into groundwater of the Pine Ridge Reservation, South Dakota
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-03
    Kenneth Swift Bird; Alexis Navarre-Sitchler; Kamini Singha

    This study integrates geochemical modeling, spatial analysis and several statistical methods including principal component analysis, multivariate regression and cluster analysis to investigate hydrogeologic controls of arsenic and uranium contamination within groundwater of the Arikaree aquifer on the Pine Ridge Reservation. Located in southwestern South Dakota, the Pine Ridge Reservation is largely rural and many people rely on domestic supply wells completed in the Arikaree aquifer as their primary drinking water source. Locally, the White River Group, which unconformably underlies the Arikaree Group, is enriched in arsenic and uranium related to volcanic ash deposits and acts as a geogenic metal source. Geochemical data from over 250 groundwater samples were obtained through collaboration with the Oglala Sioux Tribe. Cluster spatial statistics analyses delineated four regions of statistically significant variations in groundwater chemistry that represent upgradient, intermediate, and downgradient portions of the Arikaree aquifer. Groundwater evolves as it flows through the Arikaree aquifer with increasing alkalinity, sodium, and pH along flow paths. These chemical changes are likely due to dissolution of carbonate minerals and volcanic ash. Thermodynamic calculations suggest increasing supersaturation of the groundwater with respect to calcite; thus, volcanic ash dissolution may be an important secondary source of alkalinity. Elevated alkalinity and pH levels were found to be the driving factors of arsenic and uranium mobility, and downgradient sections of the aquifer in the northern portions of the PRR are most likely to be impacted by metal(loid) contamination, with 73% of the wells in this grouping failing a USEPA MCL for arsenic, uranium, and/or gross alpha.

    更新日期:2020-01-04
  • Uranium tolerant phosphate solubilizing bacteria isolated from Gogi, a proposed uranium mining site in South India
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-03
    S. Sowmya; P.D. Rekha; I. Yashodhara; N. Karunakara; A.B. Arun

    Remediation of uranium contamination presents a significant environmental problem worldwide. Bioremediation has gained increasing importance as a feasible and eco-friendly strategy. Uranium tolerant phosphate solubilizing bacteria are considered as important candidates in the development of bioremediation technology. In this context, we have isolated bacteria from a proposed uranium mining site, Gogi in the Bhima river belt of Karnataka (South India) with special reference to phosphate solubilizers. Out of 270 bacteria isolated, 14 isolates solubilized 148.5–1226.6 mg L−1 phosphate from 5 g L−1 tri-calcium phosphate accompanied by drop in media pH from an initial 6.9 to pH values between 3.9 and 6.3. Phylogenetic analysis of 14 phosphate solubilizing bacteria by 16S rRNA gene sequencing grouped them into three phyla, namely Firmicutes, Proteobacteria and Actinobacteria. When tested for uranium sensitivity, 12 of the 14 phosphate solubilizing isolates showed significant (p < 0.01) tolerance to uranium (4.1%–26.1%) compared to the reference strain Escherichia coli ATCC 25922T. This demands further in-depth studies on microbial inhabitants from such complex environmental conditions that could provide better agents and insights for remediation technology.

    更新日期:2020-01-04
  • Chemical weathering and atmospheric CO2 consumption in the semi-arid Swarnamukhi basin (Peninsular India) estimated from river water geochemistry
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-03
    Priyanka Patel; N. Janardhana Raju; V. Subramanian; Wolfgang Gossel; Peter Wycisk

    A small ephemeral Swarnamukhi River (hard rock) basin, more sensitive to climate change, was sampled and analyzed for various parameters. A total of 66 river water samples (22 of each season) were collected from different sampling stations covering the whole Swarnamukhi River basin in pre- and post- and monsoon seasons. Chemical weathering rate data of the Swarnamukhi River basin is integrated with the available data of other large perennial (Godavari and Krishna) and ephemeral (Kaveri and Periyar) hard rock river basins of Peninsular India. The Peninsular river basins, including Swarnamukhi River basin, are mainly dominated by granitic gneissic terrain. Contribution of inputs through forward modelling shows: silicate > evaporite > carbonate > atmosphere. The mean silicate and carbonate weathering rates in the river basin observed are 27.15 tonnes.km−2.yr−1 and 9.45 tonnes.km−2.yr−1 in pre-monsoon season, whereas 32.73 tonnes.km−2.yr−1and 45.90 tonnes.km−2.yr−1 in post-monsoon season, respectively. The Swarnamukhi river has lower silicate weathering rate (annual average: 30.57 tonnes.km−2.yr−1) than other published river basins data (Narmada: 33.9 tonnes.km−2.yr−1; Nethravati: 42 tonnes.km−2.yr−1; Godavari: 45.6 tonnes.km−2.yr−1) due to different localized geological setting. Mean annual CO2 consumption for the Swarnamukhi River is 6.9 × 105 mol km−2.yr−1 which is comparable to other Peninsular rivers such as the Godavari (6 × 105 mol km−2.yr−1) and Gad (5.7 × 105 mol km−2.yr−1) rivers. The study further provides the inventory for CO2 consumption on river basin scale, which is an important consideration from the global warming point of view.

    更新日期:2020-01-04
  • Geochemical barriers in oligotrophic peat bog (Western Siberia)
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-02
    Oleg Savichev; Evgeniya Soldatova; Maxim Rudmin; Aleksey Mazurov
    更新日期:2020-01-04
  • Impact of the atmospheric deposition of major acid rain components, especially NH4, on carbonate weathering during recharge in typical karst areas of the Lijiang River basin, southwest China
    Appl. Geochem. (IF 2.894) Pub Date : 2020-01-01
    Haiyan Zhu; Yongshan Li; Liangjun Wu; Shi Yu; Cunlin Xin; Pingan Sun; Qiong Xiao; Haijuan Zhao; Yong Zhang; Tong Qin
    更新日期:2020-01-04
  • Acceleration of glass alteration rates induced by zeolite seeds at controlled pH
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-28
    James J. Neeway; Benjamin P. Parruzot; Jeffrey F. Bonnett; Joelle T. Reiser; Sebastien N. Kerisit; Joseph V. Ryan; Jarrod V. Crum

    As the glass-water reaction proceeds, certain glass compositions undergo a delayed acceleration in the alteration rate – a phenomenon that is commonly referred to as Stage III behavior – which generally coincides with zeolite formation. However, studying Stage III in the laboratory is difficult because the time scale required to observe Stage III behavior can vary from months to several years, and the solution conditions that initiate this acceleration remain poorly understood. Consequently, the development of a corrosion test method capable of quantifying Stage III rates in a timely manner would be of great benefit to both the scientific community and policy makers concerned with nuclear waste disposal. In this work, we induced and measured the acceleration in the corrosion rate of the AFCI glass by seeding static corrosion tests with zeolite Na–P2 at imposed pH90°C values ranging from 9.5 to 11.5. The log10 induced Stage III rates increased linearly with increasing pH and were measured to be between the forward and residual rates of AFCI. Tests designed to compare induced Stage III rates obtained for different seeding times showed that the induced Stage III rates were faster in the absence of an alteration layer. In summary, the use of the seeded test method allows for a quantification of induced Stage III rates in a relatively short, one-month time period.

    更新日期:2020-01-04
  • Interfacial energies of supercritical CO2 and water with 2:1 layered silicate surfaces: A density functional theory study
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-27
    O.A. Ajayi; J.D. Kubicki

    Interfacial energies between supercritical CO2 (scCO2) and water with a model clay surface under conditions related to hydraulic fracturing have been investigated using density functional theory (DFT) methods. Planewave DFT methods in the program VASP (Kresse and Furthmüller, 1996) were used to perform molecular dynamics (MD) simulations at a temperature of 333.33 K to calculate these interfacial energies and molecular structures. The calculated interfacial energies between scCO2 and water with the K+-bearing model clay surface were 0.022 and 0.0422 J/m2, respectively. The lower interfacial energy between scCO2 and model clay suggests that scCO2 would create a better fracturing fluid because it can enter the nanopores of clay-dominated shales more readily than water. This entrance into nanopores before fracturing occurs could create a more complex fracture network. The orientations of the scCO2 molecules with respect to the silicate layer also suggest that scCO2 is not influenced by a charged ion surface on the surface of the silicate whereas the water is. These interfacial structures also provide insight into why scCO2 would have a lower interfacial energy with silicate than water.

    更新日期:2020-01-04
  • Wellbore cement alteration during decades of abandonment and following CO2 attack – A geochemical modelling study in the area of potential CO2 reservoirs in the Pannonian Basin
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-24
    Zsuzsanna Szabó-Krausz; Nóra Edit Gál; Viktória Gável; György Falus

    In East-Central Europe, the sedimentary rocks and saline reservoirs of the Pannonian Basin provide the greatest potential for geological sequestration of CO2. However, there is no knowledge about the integrity of cement casing and plugs in abandoned wellbores drilled in the last century, which surround the potential CO2 geological storage sites. Thermodynamic and kinetic batch, and 1D kinetic reactive transport models have been built up in PHREEQC to estimate the present composition of hydrated cement in different depths (106, 1478, 2136 and 2718 m) of these abandoned wellbores and, to access cement reactivity for the effect of potentially injected CO2. The wellbore cements are all predicted to presently consist of mainly calcium silicate hydrate (CSH) and portlandite but differences occur due to the stability of ettringite connected to the temperature of the geological environment. With the depth, the amount of potentially dissolved CO2 increases which induces the breakdown of portlandite and CSH in the cement, and the major precipitation of calcite and amorphous silica. The transformation affects the whole width of the cement casing after about 2–3 years in most of the depths. However, the calculated mass transfer among minerals indicate a 2–6% porosity drop, which raises the attention to potential pore clogging. This process significantly reduces the risks of abandoned wellbores when implementing CO2 geological storage.

    更新日期:2020-01-04
  • Evaluation of groundwater hydrogeochemical characteristics and delineation of geothermal potentialities using multi criteria decision analysis: Case of Tozeur region, Tunisia
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-19
    Fatma Ben Brahim; Emna Boughariou; Jalila Makni; Salem Bouri

    The use of geothermal energy in Tunisia is limited to its instant use because of the low enthalpy resources, especially in the southern part of the country. The Djerid Basin has remarkable geothermal resources with low to moderate temperatures that have been used only for irrigation of oases and heating greenhouses. In order to evaluate the geothermal potential of groundwater resources of Tozeur region located in the Djerid Basin, a synthetic approach including geological, geophysical, physicochemical, hydrogeological and geothermometric characteristics of groundwater is indispensable. It aims to determine: (1) the evolution of the water chemistry, (2) the origin of thermal waters and their reservoir temperature, (3) the mixing mechanism of geothermal fluid and (4) the mapping of geothermal potentialities with Multi-Criteria Decision-Analysis (MCDA) using GIS platform. The hydrogeochemical approach revealed that the studied geothermal system is characterized by temperature values ranging between 25 and 75 °C and total dissolved solids (TDS) values between 0.7 and 5.8 g/l. Furthermore, the use of silica geothermometers and saturation indices for different solid phases gave estimated geothermal reservoir temperature ranging between 92 and 104 °C and between 100 and 125 °C, respectively. In addition, the equilibrium processes elucidated that the thermal waters are mostly in the oversaturated condition with respect to calcite, aragonite and dolomite, but they are saturated with evaporate minerals. The use of geothermal energy in Tunisia is limited to the direct application because of the low enthalpy resources, especially in the southern part of the country. The Djerid Basin has remarkable geothermal resources with low to moderate temperatures that have been used only for irrigation of oases and heating greenhouses. In order to evaluate the geothermal potential of groundwater resources of Tozeur region located in the Djerid Basin, a synthetic approach including geological, geophysical, physicochemical, hydrogeological and geothermometric characteristics of groundwater is indispensable. It aims to delineate: (1) the water chemistry evolution, (2) the origin of thermal waters and their reservoir temperature, (3) the mixing mechanism of geothermal fluid and (4) the mapping of geothermal potentialities with Multi-Criteria Decision-Analysis (MCDA) using GIS platform. The hydrogeochemical approach revealed that the studied geothermal system is characterized by temperature values ranging between 25 and 75 °C and total dissolved solids (TDS) values between 0.7 and 5.8 g/l. On the other hand, the use of silica geothermometers and saturation indices for different solid phases gave estimated geothermal reservoir temperature ranging between 92 and 104 °C and between 100 and 125 °C, respectively. Furthermore, equilibrium processes elucidated that the thermal waters are mostly in the oversaturated condition with respect to calcite, aragonite and dolomite, but they are saturated with evaporate minerals. According to the obtained results of the MCDA, the spatial assessment of the potential geothermal areas using Weighted Overlay and Boolean logic Models are 37% and 5% respectively. The findings in this study contribute to a better understanding of groundwater sustainability for supporting geothermal project on renewable energy and can be used as a synthetic document for realistic management of groundwater resources.

    更新日期:2020-01-04
  • Molecular dynamics simulation of the interaction of uranium (VI) with the C–S–H phase of cement in the presence of gluconate
    Appl. Geochem. (IF 2.894) Pub Date : 2019-12-18
    Iuliia Androniuk; Andrey G. Kalinichev

    Due to their high durability and immobilization properties, cementitious materials have found a considerable application in the design and construction of radioactive waste repositories in the last decades. During cement paste production, organic additives are introduced to modify various properties of cement. The presence of such organic complexants may negatively affect the immobilizing properties of cement with respect to radionuclides. For better understanding and prediction of the effects of interactions between organic molecules and cementitious materials with radionuclides, we have developed several representative models consisting of three principal components: (i) calcium silicate hydrate (C–S–H) phase - the main binding phase of cement; (ii) gluconate, a simple well-described molecule, as a representative of organic additives; (iii) U(VI), as one of the most studied radionuclides of the actinide series. The C–S–H phase with low Ca/Si ratio (∼0.83) typical for “low-pH” and degraded cement pastes has been selected for this modelling study. Structural, and energetic aspects of the sorption processes of uranyl, gluconate, and their mutual correlations on the surface of cement were quantitatively modeled by classical molecular dynamics (MD) and potential of mean force (PMF) calculations. The ternary surface complex formation between uranyl hydroxides and Ca2+ cations at the C–S–H aqueous interfaces is shown to have an important role in the overall sorption process. In the presence of gluconate, U(VI) sorption on C–S–H is facilitated by weakening the Ca2+ binding with the surface. Additionally, Na+ is proven to be an important competitor for certain surface sorption sites and can potentially affect the equilibrium properties of the interface.

    更新日期:2020-01-04
  • Fe(III) uptake by calcium silicate hydrates
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-26
    A. Mancini; E. Wieland; G. Geng; R. Dähn; J. Skibsted; B. Wehrli; B. Lothenbach

    Wet chemistry and spectroscopic investigations were conducted to study Fe(III) uptake by calcium silicate hydrate (C–S–H) at different Ca/Si ratios. Wet chemistry experiments were carried out by using a 55Fe radiotracer while 29Si NMR and XAS spectroscopy were performed on C–S–H phases loaded with different Fe(III) concentrations. Sorption kinetics experiments indicate that equilibrium was attained within 30 days. Over the studied concentration range, Fe(III) sorption was linear, irrespective of the difference in pH of the suspension and the Ca/Si of C–S–H. In addition, Fe(III) sorption on C–S–H phases was significantly stronger than Al(III) sorption. The total Fe(III) uptake by C–S–H phases, however, was limited by the lower solubility of Fe(OH)3 compared to Al(OH)3; up to 1 mol Fe/kg C–S–H (molar Fe(III)/Si ≈ 0.001) could be taken up. 29Si NMR and EXAFS data suggest Fe(III) uptake in octahedral coordination into the interlayer of the C–S–H phases with Ca/Si ratios 1.2 and 1.5. However, such an uptake mechanism appears unlikely in the case of the C–S–H phase with Ca/Si 0.8 because structural parameters of Fe(III) deduced from EXAFS are different.

    更新日期:2020-01-04
  • Impact glass applied as a standard for long-term performance assessment of Na–Ba borosilicate glass forms in geological environment
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-23
    Amit Kumar; J.P. Shrivastava; Meenakshi; Sundeep Chopra; Sattam Chakraborty
    更新日期:2020-01-04
  • Sources and historical sedimentary record: Temporal variability of n-alkane and PAHs from the Yellow River Estuary, China
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-21
    Chuanyuan Wang; Liangju Yu; Yanmei Zou; Ling Ji; Yuanwei Li

    The composition and distribution of n-alkanes and polycyclic aromatic hydrocarbons (PAHs) in suspended particulate matter (SPM) from the Yellow River and a sedimentary core from the Yellow River Estuary, China, were measured in order to determine environmental changes in the Yellow River Estuary on a regional scale. The concentration of n-alkane in SPM increased along the upper-middle-lower reaches of the Yellow River. The total concentrations of n-alkanes and PAHs in the core ranged from 0.04 to 0.86 μg g−1 (avg. 0.21 μg g−1), and from 0.04 to 0.29 μg g−1 (avg. 0.15 μg g−1) on a dry wt. basis, respectively. Understanding the temporal evolution of n-alkanes provide information on terrigenous versus aquatic productivity, oil exploration at the Shengli Oilfield, and channel diversion in the Yellow River. n-Alkanes in SPM were mainly derived from mixed sources, with terrigenous inputs dominating. PAHs in the sediment core were predominantly derived from coal and biomass combustion. The variation in PAHs levels throughout the core determines changes in energy use and socio-economic development. The temporal variability in n-alkane and PAHs and their molecular diagnostic ratios revealed a trend of regional environmental change and the role of anthropogenic activity in that environmental change.

    更新日期:2020-01-04
  • Vanadium-rich slags from the historical processing of Zn–Pb–V ores at Berg Aukas (Namibia): Mineralogy and environmental stability
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-20
    Vojtěch Ettler; Martin Mihaljevič; Alice Jarošíková; Adam Culka; Bohdan Kříbek; Vladimír Majer; Aleš Vaněk; Vít Penížek; Ondra Sracek; Ben Mapani; Fred Kamona
    更新日期:2020-01-04
  • ‘Co-evolution’ of uranium concentration and oxygen stable isotope in phosphate rocks
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-20
    Y. Sun; W. Amelung; B. Wu; S. Haneklaus; M. Maekawa; A. Lücke; E. Schnug; R. Bol

    Phosphate rocks (PRs) used in fertilizer production contain uranium (U), which enters agricultural soils through phosphorus fertilization. However, our knowledge is still limited and cannot explain the different levels of U contamination found in agricultural systems. The paper reviewed the spatial and temporal U variations in PRs to obtain a comprehensive overview of U levels in various PRs worldwide and to investigate why U concentrations in igneous PRs are significantly lower compared to sedimentary PRs, and why less U is present in old sedimentary PRs (Precambrian-Cambrian) than in younger PRs (Ordovician-Neogene). In addition, the natural oxygen isotope compositions of phosphate (δ18Op) in various PRs were determined to identify their origins in relation to their U concentration. The δ18Op values differed among igneous PRs, old sedimentary PRs, and younger sedimentary PRs. Generally, the PRs with low δ18Op values had low U concentrations. In igneous PRs, low U concentrations were due to the lack of secondary U enrichment processes after rock formation, with low δ18Op values resulting from limited isotope fractionation at high temperature. Conversely, in sedimentary PRs, both U concentrations and δ18Op values were influenced by paleoclimate and paleogeographic features. Overall, there is a time-dependent coincidence of processes altering U concentration and δ18Op signatures of sedimentary PRs in a similar direction.

    更新日期:2020-01-04
  • Volcanic glass leaching and the groundwater geochemistry on the semi-arid Atlantic island of Porto Santo
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-18
    Maria Teresa Condesso de Melo; Raghwendra Narayan Shandilya; João Baptista Pereira Silva; Dieke Postma

    The groundwater chemistry of the semi-arid volcanic island of Porto Santo, part of the Madeira archipelago, Atlantic Ocean, was investigated. Generally, the groundwater was brackish, containing 2–10 mol % seawater. Groundwater with up to 20 mM alkalinity and a Na enrichment of up to 30 mM, as compared to the Na concentration predicted by the seawater Na/Cl ratio, was found in the main aquifer. Also notable are the high concentrations of F (up to 0.3 mM), B (up to 0.55 mM), As (up to 0.35 μM), all in excess of WHO recommendations, as well as up to 6 μM V. Geochemical modeling, using the PHREEQC code, was used to explore different scenarios that could explain the genesis of the observed bulk groundwater chemistry. First, a model for aquifer freshening with the displacement of resident seawater from the aquifer by infiltrating freshwater, was tested. This scenario leads to the development of NaHCO3 waters as observed in many coastal aquifers. However, the measured alkalinity concentration in the groundwater was far higher than the concentration predicted by the freshening model. In addition, the behavior of modelled pH and PCO2 were at variance with their distributions in the field data. The second model explored the possible effect of volcanic glass leaching on the groundwater chemistry. Using insight derived from studies of volcanic glass surface alteration as well as experimental work on water-volcanic glass interactions, a geochemical model was developed in which the exchange of H+ for Na+ on the volcanic glass surface is the main mechanism but the exchange of other cations on the volcanic glass surface is also included. The uptake of H+ by the glass surface causes the dissociation of carbonic acid, generating bicarbonate. This model is consistent with the local geology and the field data. It requires, however, volcanic glass leaching to occur in the unsaturated zone where there is an unlimited supply of CO2. The exchange reaction of H+ for Na+ is confined to the surface layer of volcanic glass as otherwise the process becomes limited by slow solid state diffusion of H+ into the glass and Na+ out of the glass. Therefore, volcanic ash deposits, with their high volcanic glass surface areas and matrix flow, are the aquifers where this type of high NaHCO3 waters can be expected, rather than in basalts, which predominantly feature fracture flow. The trace components F, B, As and V are believed to originate from hyaloclastites, consisting of predominantly (90%) of trachy-rhyolite volcanic glass. Although stratigraphically older than the main calcarenite aquifer, topographically they are often located at higher altitudes, above the phreatic level and located along the main recharge flow path. In addition, the semi-arid climate conditions provide a long groundwater residence time for the reactions as well as limited aquifer flushing.

    更新日期:2020-01-04
  • Evaluating biogeochemical indicators of methanogenic conditions and thermodynamic constraints in peat
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-15
    Simona Bonaiuti; Christian Blodau; Klaus-Holger Knorr

    Burial of organic matter in deep peat deposits has already been experimentally demostrated to slow down or even inhibit anaerobic decomposition due to lack of diffusive transport and end-product accumulation. However, so far little is known about potential biogeochemical or thermodynamic indicators for the observed inhibition of further decomposition. For example, theoretical energy yields for methanogenesis, hydrogen partial pressures, stable isotope fractionation factors between CO2 and CH4, and electrochemical properties of dissolved organic matter have been proposed as thermodyamic indicators for such inhibition. To test the applicability and explanatory power of these indicators to identify conditions inhibiting organic matter decomposition, we incubated homogenized ombrotrophic peat for 300 days at 20 °C under diffusive flux conditions as control, and compared the observed effects to a treatment with vertical advective transport by water circulation and to a treatment in which both the unsaturated and water-saturated zone of the peat profile were kept anoxic. Results of energy yields of acetoclastic and hydrogenotrophic methanogenesis were compared to hydrogen partial pressures, to 13C isotope fractionation factors and to redox properties of dissolved organic matter as obtained from mediated electrochemical oxidation and reduction. While CO2 and CH4 production slowed substantially in the deep peat profile, a concomitant decrease of Gibs free energy yields available to hydrogenotrophic and acetoclastic methanogensis and hydrogen and acetate concentrations over time supported a thermodynamic constraint on methanogenesis. Although, energy yields for the hydrogenotrophic pathway were close to or below the theoretical energy minimum levels already after 15 days. Transiently elevated H2 concentrations, not related to actual methanogenesis rates were observed for about 150–225 days. Thereafter, hydrogen concentrations diminished to levels below thresholds to thermodynamically support ongoing methanogenesis. Thus even on incubation timescales of 150–225 days, steady-state hydrogen concentrations as would be expected from thermodynamic considerations did not adjust on the bulk scale of observation. Gibbs free energy estimates for methanogenesis based on hydrogen partial pressures were consequently biased and did not reach the minimum required threshold despite ovious net CH4 production. Ratios between electron accepting (EAC) and donating (EDC) capacity of dissolved organic matter, however, turned out to provide suitable indicators of predominant redox conditions along gradients, stabilizing at low values upon onset of methanogenesis. Thus, our study demonstrated that the thermodynamically driven slow down of decomposition in deep peat deposits, preventing the peat to decompose further, cannot be easily identified based on a single indicator. However, constant and high concentrations of decomposition end-products, indicating zero net turnover and low energy yields, and constantly low EAC/EDC ratios, indicating no further availability of terminal electron acceptors, seem to be characteristic of the onset of conditions inhibiting further significant decomposition of peat.

    更新日期:2020-01-04
  • Geochemical signature of superhigh organic sulphur Raša coals and the mobility of toxic trace elements from combustion products and polluted soils near the Plomin coal-fired power station in Croatia
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-15
    Nir Roy Lieberman; Maria Izquierdo; Carmen Muñoz-Quirós; Haim Cohen; Simon R. Chenery

    In the northern Adriatic coast of Croatia, combustion of super-high organic sulphur rich Raša coal was common between 1970 and 2000. These Late Paleocene coals are enriched in a number of trace elements. This work aims to provide a detailed study on the distinctive geochemical patterns of the Raša coal and investigate the environmental effects of the coal and combustion by-products on the area. Several analytical techniques were used to study the mode of occurrence, distribution, levels and solubility of major and trace elements in the Raša coal, fly ash, slag and soils in an area within 10 km from the power station. Due to the sulphur-rich calcareous depositional environment of the Raša coal, the combustion by-products are enriched in S and Ca. Fly ash and slag are enriched in potentially harmful trace elements i.e. Se, Mo, Hg, V and U. Similar enrichment pattern was found for soils suggesting that resuspension and deposition of airborne coal and fly ash particles, transport of gaseous species in the flue gas by dominant winds and/or leaching from ash deposits may have affected the wider environment. Whilst a large number of trace elements were found to be poorly soluble across samples, the leachable concentrations of Se, Cr and Mo in fly ash and slag are noteworthy. Their organic association in coal enhances volatilisation during combustion and then further condensation on ash particles as readily soluble oxyanionic species. Other oxyanionic metalloids such as As or V were insoluble in fly ash and slag, due to precipitation of solubility-limiting Ca-bearing species.

    更新日期:2020-01-04
  • Uranyl(VI) sorption in calcium silicate hydrate phases. A quantum chemical study of tobermorite models
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-09
    Alena Kremleva; Sven Krüger; Notker Rösch
    更新日期:2020-01-04
  • Variations and influence factors of 210Pb-specific radioactivity in modern calcite depositions in a subtropical cave, South China
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-09
    Wei Tang; Gaoyong Lan; Hui Yang; Jian-Jun Yin; Junbing Pu

    Although 210Pb dating has been successfully used in speleothems, the understanding of the factors impacting 210Pb variations in modern calcite depositions in karst caves is poor due to the lack of in situ monitoring. Here, we studied the 210Pb variations in drip water and modern calcite depositions at five sampling sites in Maomaotou Big Cave in Guilin, south China, through more than three years of in situ monitoring. In this work, the air 222Rn concentrations, weights and 210Pb-specific radioactivity of modern calcite depositions showed significant temporal and spatial variations. The modern calcite deposition weights and 222Rn concentrations in the air of Maomaotou Big Cave ranged from 0.02 to 6.04 g and 62.9–628 Bq.m−3 (higher values in summer-autumn and lower values in winter–spring), respectively, while the 210Pb-specific radioactivities in calcite depositions varied from 7.33 to 658.52 Bq•kg−1, with lower values reported in summer–autumn and higher values in winter–spring. The opposite seasonal trends observed for the 222Rn concentrations and 210Pb-specific radioactivity indicated that the air 222Rn concentration was not the dominant factor influencing the 210Pb-specific radioactivity in the modern calcite depositions. This study concluded that 210Pb-specific radioactivity in modern calcite depositions is mainly carried by drip water; further, the remarkable negative correlation between deposition weight and 210Pb-specific radioactivity in modern calcite depositions suggests that the Constant Initial Concentration model (CIC) is fit for recent speleothem dating in a closed system. Such important information may provide a scientific basis for cave deposition dating using 210Pb.

    更新日期:2020-01-04
  • Geochemical characteristics of pore waters from sediment cores of the Wagner Basin, Gulf of California
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-09
    Ramón Yosvanis Batista Cruz; Loïc Peiffer; Bodo Weber; Juan Carlos Herguera; Marcello Liotta; Antonio González Fernández; Rosa María Barragán Reyes; Thomas Gunter Kretzschmar

    The Wagner Basin (WB) is a shallow basin (depth < 225 m) belonging to the northernmost section of the Gulf of California rift system. Hydrothermal activity and high heat fluxes prevail in some regions of the WB. For this contribution, we report the first dataset of chemical (major and some trace elements) and isotopic compositions (δ18O, δD, 87Sr/86Sr, δ13C) from pore water sampled at the bottom of the WB, in areas affected by hydrothermal activity. The goals of the study are to determine the origin of the fluids emanating from the anomalous heat flow zones and to characterize the physical and chemical processes controlling their composition. The 18 pore water samples are classified into two groups: low temperature (LT) and high temperature (HT) samples, according to the sampling temperature (from 16.4 to 25.6 °C, and 32.5–99.6 °C, respectively). LT samples have chemical and isotopic (δ18O and δD) compositions similar to those of present-day seawater. On the opposite, HT cores are typically more enriched in Cl (26,100–37,074 mg L−1) and other elements (Br, Na, K, Ca, B and Sr) than those of present-day seawater (Cl = 20,284 mg L−1). HT samples are also strongly depleted in deuterium isotopes (up to −30.48‰). This characteristic could be related to the mixing between ancient evaporated seawater and Colorado river waters. Conceptually, the origin of a saline paleo-aquifer/reservoir can be related with the gradual marine flooding of shallow lagoons and depressions at the time Gulf of California was rifting (6–8 Ma) or during the Last Glacial Maximum (20–26 Ky). Additionally, it is not ruled out that some of the deuterium depletion observed in HT samples may be related to secondary processes (e.g., clays exchange, organic matter). Radiogenic 87Sr/86Sr signatures (0.70929–0.70997) of the HT samples likely reflect the leaching of radiogenic continental sediments from the Colorado River (filling the WB) and authigenic minerals (e.g., calcite or barite) precipitated from seawater. Solute geothermometry indicates that HT pore fluids underwent water-rock interactions at temperature of at least 220 °C. Finally high δ13C values (up to +10.5‰) in DIC from HT samples indicates partial equilibration of methane with DIC, or partial reduction of DIC.

    更新日期:2020-01-04
  • The role of Al13-polymers in the recovery of rare earth elements from acid mine drainage through pH neutralization
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-09
    M.L.B. Moraes; A. Murciego; E. Álvarez-ayuso; A.C.Q. Ladeira
    更新日期:2020-01-04
  • Clay mineral solubility from aqueous equilibrium: Assessment of the measured thermodynamic properties
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-09
    S. Gaboreau; H. Gailhanou; Ph Blanc; Ph Vieillard; B. Made

    Clay minerals (kaolinite KGa-2, smectite MX-80, illite IMt-2, vermiculite SO and Chlorite Cca-2) were equilibrated in aqueous media during long-term batch experiments up to seven years. Dissolved element concentrations were measured, allowing calculation of the ionic activity product of the minerals. An improved protocol for equilibration has been established to limit evaporation over the seven years of the experiments and to optimize the analytical results accuracy. The protocol could be verified with respect to the solubility of kaolinite. For the other minerals, the equilibrium constants obtained could be compared with the values calculated after calorimetric measurements previously performed on the same samples. The ionic activity products extracted for illite, smectite and, to a lesser extent, vermiculite were found to agree with the values issued from the calorimetric measurements. For chlorite in particular, a discrepancy with calorimetric measurements still remains. This was interpreted in terms of dissolution rates getting slower for this mineral, formed at temperatures higher than 25 °C.

    更新日期:2020-01-04
  • Water quality impacts of in-stream mine tailings on a headwater tributary of the Rio Pilcomayo, Potosí, Bolivia
    Appl. Geochem. (IF 2.894) Pub Date : 2019-11-05
    Jing Sun; William H.J. Strosnider; Robert W. Nairn; Julie A. LaBar

    Rio Tarapaya, a major tributary of the upper Rio Pilcomayo and a crucial water resource in the arid Southeastern Bolivian highlands, has been impacted by in-stream mine tailings and acid rock drainage over the past five centuries, from historic and ongoing mining at Cerro Rico de Potosí. Identification of the effects of in-stream mine tailings on the waters of Rio Tarapaya is essential to better understand the dynamics of these complex systems and propose successful management strategies. A study was performed on river waters and sediments at six sites in a reach of Rio Tarapaya, beginning at the city limits of Potosí and ending just after the confluence with Rio Cayara, a relatively unimpaired river 7.3 km downstream. Concentrations of dissolved metals (such as Fe, Al, Mn, and As) in the Ca–Mg–HCO3–SO4 dominated stream were generally orders of magnitude greater than Bolivian receiving water body criteria and United Nations Food and Agriculture Organization irrigation and livestock drinking water guidelines. Variability of Ca and Mg in water and sediment was controlled by dissolution of gypsum, dolomite and calcite, which was supported by Spearman correlation coefficients. The primary ionic products of in-stream sulfide mineral weathering (SO42−, Fe, Al, Mn, Zn and As), are the dominant ions of stream water and sediment leachate. Results are consistent with PHREEQC modeling of minerals such as gibbsite, melanterite, goethite, calcite and dolomite. In general, the reactivity of bed material increased and stream water quality decreased with increasing distance from Potosí. Metals and metalloids are spiraling downstream via seasonally driven particle transport, sulfide weathering, and salt dissolution coupled with biotic interactions. The reactivity of the millions of tonnes of in-stream tailings in Rio Tarapaya and persistence of contemporary illicit tailings discharges indicates that the upper Rio Pilcomayo will remain severely degraded for the foreseeable future unless substantial remediation is undertaken.

    更新日期:2020-01-04
  • Amino acid abundances and stereochemistry in hydrothermally altered sediments from the Juan de Fuca Ridge, northeastern Pacific Ocean.
    Appl. Geochem. (IF 2.894) Pub Date : 2007-07-28
    E Andersson,B R Simoneit,N G Holm

    The Juan de Fuca Ridge is a hydrothermally active, sediment covered, spreading ridge situated a few hundred kilometres off the west coast of North America in the northeastern Pacific Ocean. Sediments from seven sites drilled during the Ocean Drilling Program (ODP) Legs 139 and 168 were analyzed for total hydrolyzable amino acids (THAA), individual amino acid distributions, total organic C (TOC) and total N (TN) contents. The aim was to evaluate the effects of hydrothermal stress on the decomposition and transformation of sedimentary amino acids. Hydrolyzable amino acids account for up to 3.3% of the total organic C content and up to 12% of the total N content of the upper sediments. The total amounts of amino acids decrease significantly with depth in all drilled holes. This trend is particularly pronounced in holes with a thermal gradient of around 0.6 degrees C/m or higher. The most abundant amino acids in shallow sediments are glycine, alanine, lysine, glutamic acid, valine and histidine. The changes in amino acid distributions in low temperature holes are characterized by increased relative abundances of non-protein beta-alanine and gamma-aminobutyric acid. In high temperature holes the amino acid compositions are characterized by high abundances of glycine, alanine, serine, ornithine and histidine at depth. D/L ratios of samples with amino acid distributions similar to those found in acid hydrolysates of kerogen, indicate that racemization rates of amino acids bound by condensation reactions may be diminished.

    更新日期:2019-11-01
  • Hydrothermal petroleum from lacustrine sedimentary organic matter in the East African Rift.
    Appl. Geochem. (IF 2.894) Pub Date : 2007-07-28
    B R Simoneit,T A Aboul-Kassim,J J Tiercelin

    Cape Kalamba oil seeps occur at the south end of the Ubwari Peninsula, at the intersection of faults controlling the morphology of the northern basin of the Tanganyika Rift, East Africa. Oil samples collected at the surface of the lake 3-4 km offshore from Cape Kalamba have been studied. The aliphatic hydrocarbon and biomarker compositions, with the absence of the typical suite of polynuclear aromatic hydrocarbons, indicate an origin from hydrothermal alteration of immature microbial biomass in the sediments. These data show a similarity between a tar sample from the beach and the petroleum from the oil seeps, and confirm that the source of these oils is from organic matter consisting mainly of bacterial and degraded algal biomass, altered by hydrothermal activity. The compositions also demonstrate a < 200 degrees C temperature for formation/generation of this hydrothermal petroleum, similar to the fluid temperature identified for the Pemba hydrothermal site located 150 km north of Cape Kalamba. The 14C age of 25.6 ka B.P. obtained for the tar ball suggests that Pleistocene lake sediments could be the source rock. Hydrothermal generation may have occurred slightly before 25 ka B.P., during a dry climatic environment, when the lake level was lower than today. These results also suggest that the Cape Kalamba hydrothermal activity did not occur in connection with an increased flux of meteoric water, higher water tables and lake levels as demonstrated in the Kenya Rift and for the Pemba site. Hydrothermal petroleum formation is a facile process also in continental rift systems and should be considered in exploration for energy resources in such locales.

    更新日期:2019-11-01
  • Manganese redox buffering limits arsenic release from contaminated sediments, Union Lake, New Jersey.
    Appl. Geochem. (IF 2.894) Pub Date : 2017-12-15
    Alison R Keimowitz,Brian J Mailloux,Karen Wovkulich,Jennifer Harkness,James M Ross,Steven N Chillrud

    The sediments of Union Lake in Southern New Jersey are contaminated with arsenic released from the Vineland Chemical Company Superfund site 11 km upstream. Seasonal anoxia has been shown to release arsenic from sediments to similar lakes; this process was hypothesized as a major arsenic source to Union Lake. Data indicate, however, that releases of arsenic to bottom waters from the sediments or from pore waters within the sediments are relatively minor: bottom water arsenic concentrations reached ~30 ppb (~12 μM) at most, representing <13% of the dissolved arsenic content of the lake. Manganese concentrations increase more quickly and to higher levels than arsenic and iron concentrations; maximum [Mn]= ~13 ppm (~250 μM), maximum [Fe] = ~6 ppm (~120 μM). Incubation experiments support the hypothesis that manganese acts as a redox buffer and prevents large arsenic releases. Under the observed conditions, little of the arsenic in the water column is from contaminated sediment. This study also suggests that arsenic release from sediment to lake water may be more important in lakes that remain anoxic more continuously.

    更新日期:2019-11-01
  • Reversible adsorption and flushing of arsenic in a shallow, Holocene aquifer of Bangladesh.
    Appl. Geochem. (IF 2.894) Pub Date : 2017-05-02
    Kathleen A Radloff,Yan Zheng,Martin Stute,Beth Weinman,Benjamin Bostick,Ivan Mihajlov,Margaret Bounds,M Moshiur Rahman,M Rezaul Huq,Kazi M Ahmed,Peter Schlosser,Alexander van Geen

    The spatial heterogeneity of dissolved arsenic (As) concentrations in shallow groundwater of the Bengal Basin has been attributed to transport of As (and reactive carbon) from external sources or to the release of As from within grey sand formations. We explore the latter scenario in this detailed hydrological and geochemical study along a 300 m transect of a shallow aquifer extending from a groundwater recharge area within a sandy channel bar to its discharge into a nearby stream. Within the 10-20 m depth range, groundwater ages along the transect determined by the 3H-3He method increase from <10 yr in the recharge area to a maximum of 40 yr towards the stream. Concentrations of groundwater As within the same grey sands increase from 10 to 100 to ∼500 µg/L along this transect. Evidence of reversible adsorption of As between the groundwater and sediment was obtained from a series of push-pull experiments, traditional batch adsorption experiments, and the accidental flooding of a shallow monitoring well. Assuming reversible adsorption and a distribution coefficient, Kd, of 0.15-1.5 L/kg inferred from these observations, a simple flushing model shows that the increase in As concentrations with depth and groundwater age at this site, and at other sites in the Bengal and Red River Basins, can be attributed to the evolution of the aquifer over 100-1000 years as aquifer sands are gradually flushed of their initial As content. A wide range of As concentrations can thus be maintained in groundwater with increases with depth governed by the history of flushing and local recharge rates, without external inputs of reactive carbon or As from other sources.

    更新日期:2019-11-01
  • Evidence of Decoupling between Arsenic and Phosphate in Shallow Groundwater of Bangladesh and Potential Implications.
    Appl. Geochem. (IF 2.894) Pub Date : 2017-02-28
    Z Aziz,B C Bostick,Y Zheng,M R Huq,M M Rahman,K M Ahmed,A van Geen

    Reductive dissolution of iron oxyhydroxides and reduction of arsenic are often invoked as leading causes of high dissolved As levels in shallow groundwater of Bangladesh. The second of these assumptions is questioned here by comparing the behavior As and phosphate (P), a structural analogue for As (V) which also adsorbs strongly to Fe oxyhydroxides but is not subject to reduction. The first line of evidence is provided by a detailed groundwater time-series spanning two years for three wells in the 6-9 m depth range showing removal of As(III) from shallow groundwater during the monsoon without of loss of P. The data indicate a loss of ~90% of the dissolved As from groundwater in the intermediate well relative to a level of 3 μmol/L As predicted by conservative mixing between groundwater sampled from the shallower and the deeper well. In contrast, P concentrations of ~30 μmol/L in the intermediate well closely match the prediction from conservative mixing. Reduction therefore appears to inhibit the release of As to groundwater at this site relative to P instead of enhancing it. A re-analysis of existing groundwater As and P data from across the country provides a broader context for this finding and confirms that, without reduction, elevated concentrations of As would probably be even more widespread in shallow aquifers of Bangladesh. Without providing definite proof, X-ray absorption spectroscopy of sediment from the time-series site and elsewhere suggests that the loss of As from groundwater may be coupled to precipitation of As sulfide. Further study is needed to assess the implications of these observations for shallow aquifers that have been subjected to increased withdrawals for irrigation in recent decades.

    更新日期:2019-11-01
  • Redox Zonation and Oscillation in the Hyporheic Zone of the Ganges-Brahmaputra-Meghna Delta: Implications for the Fate of Groundwater Arsenic during Discharge.
    Appl. Geochem. (IF 2.894) Pub Date : 2016-02-09
    Hun Bok Jung,Yan Zheng,Mohammad W Rahman,Mohammad M Rahman,Kazi M Ahmed

    Riverbank sediment cores and pore waters, shallow well waters, seepage waters and river waters were collected along the Meghna Riverbank in Gazaria Upazila, Bangladesh in Jan. 2006 and Oct.-Nov. 2007 to investigate hydrogeochemical processes controlling the fate of groundwater As during discharge. Redox transition zones from suboxic (0-2 m depth) to reducing (2-5 m depth) then suboxic conditions (5-7 m depth) exist at sites with sandy surficial deposits, as evidenced by depth profiles of pore water (n=7) and sediment (n=11; diffuse reflectance, Fe(III)/Fe ratios and Fe(III) concentrations). The sediment As enrichment zone (up to ~700 mg kg-1) is associated with the suboxic zones mostly between 0-2 m depth and less frequently between 5-7 m depth. The As enriched zones consist of several 5 to 10 cm-thick dispersed layers and span a length of ~5-15 m horizontally from the river shore. Depth profiles of riverbank pore water deployed along a 32 m transect perpendicular to the river shore show elevated levels of dissolved Fe (11.6±11.7 mg L-1) and As (118±91 μg L-1, mostly as arsenite) between 2-5 m depth, but lower concentrations between 0-2 m depth (0.13±0.19 mg L-1 Fe, 1±1 μg L-1 As) and between 5-6 m depth (1.14±0.45 mg L-1 Fe, 28±17 μg L-1 As). Because it would take more than a few hundred years of steady groundwater discharge (~10 m yr-1) to accumulate hundreds of mg kg-1 of As in the riverbank sediment, it is concluded that groundwater As must have been naturally elevated prior to anthropogenic pumping of the aquifer since the 1970s. Not only does this lend unequivocal support to the argument that As occurrence in the Ganges-Brahmaputra-Meghna Delta groundwater is of geogenic origin, it also calls attention to the fate of this As enriched sediment as it may recycle As into the aquifer.

    更新日期:2019-11-01
  • Toxic metal(loid) speciation during weathering of iron sulfide mine tailings under semi-arid climate.
    Appl. Geochem. (IF 2.894) Pub Date : 2015-11-10
    Robert A Root,Sarah M Hayes,Corin M Hammond,Raina M Maier,Jon Chorover

    Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg-1 (3080, 2200, and 2570 mg kg-1), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0-35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface.

    更新日期:2019-11-01
  • Biogenic nano-magnetite and nano-zero valent iron treatment of alkaline Cr(VI) leachate and chromite ore processing residue.
    Appl. Geochem. (IF 2.894) Pub Date : 2015-06-26
    Mathew P Watts,Victoria S Coker,Stephen A Parry,Richard A D Pattrick,Russell A P Thomas,Robert Kalin,Jonathan R Lloyd

    Highly reactive nano-scale biogenic magnetite (BnM), synthesized by the Fe(III)-reducing bacterium Geobacter sulfurreducens, was tested for the potential to remediate alkaline Cr(VI) contaminated waters associated with chromite ore processing residue (COPR). The performance of this biomaterial, targeting aqueous Cr(VI) removal, was compared to a synthetic alternative, nano-scale zero valent iron (nZVI). Samples of highly contaminated alkaline groundwater and COPR solid waste were obtained from a contaminated site in Glasgow, UK. During batch reactivity tests, Cr(VI) removal from groundwater was inhibited by ∼25% (BnM) and ∼50% (nZVI) when compared to the treatment of less chemically complex model pH 12 Cr(VI) solutions. In both the model Cr(VI) solutions and contaminated groundwater experiments the surface of the nanoparticles became passivated, preventing complete coupling of their available electrons to Cr(VI) reduction. To investigate this process, the surfaces of the reacted samples were analyzed by TEM-EDX, XAS and XPS, confirming Cr(VI) reduction to the less soluble Cr(III) on the nanoparticle surface. In groundwater reacted samples the presence of Ca, Si and S was also noted on the surface of the nanoparticles, and is likely responsible for earlier onset of passivation. Treatment of the solid COPR material in contact with water, by addition of increasing weight % of the nanoparticles, resulted in a decrease in aqueous Cr(VI) concentrations to below detection limits, via the addition of ⩾5% w/w BnM or ⩾1% w/w nZVI. XANES analysis of the Cr K edge, showed that the % Cr(VI) in the COPR dropped from 26% to a minimum of 4-7% by the addition of 5% w/w BnM or 2% w/w nZVI, with higher additions unable to reduce the remaining Cr(VI). The treated materials exhibited minimal re-mobilization of soluble Cr(VI) by re-equilibration with atmospheric oxygen, with the bulk of the Cr remaining in the solid fraction. Both nanoparticles exhibited a considerable capacity for the remediation of COPR related Cr(VI) contamination, with the synthetic nZVI demonstrating greater reactivity than the BnM. However, the biosynthesized BnM was also capable of significant Cr(VI) reduction and demonstrated a greater efficiency for the coupling of its electrons towards Cr(VI) reduction than the nZVI.

    更新日期:2019-11-01
  • Effect of silicic acid on arsenate and arsenite retention mechanisms on 6-L ferrihydrite: A spectroscopic and batch adsorption approach.
    Appl. Geochem. (IF 2.894) Pub Date : 2014-11-11
    Xiaodong Gao,Robert A Root,James Farrell,Wendell Ela,Jon Chorover

    The competitive adsorption of arsenate and arsenite with silicic acid at the ferrihydrite-water interface was investigated over a wide pH range using batch sorption experiments, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, extended X-ray absorption fine structure (EXAFS) spectroscopy, and density functional theory (DFT) modeling. Batch sorption results indicate that the adsorption of arsenate and arsenite on the 6-L ferrihydrite surface exhibits a strong pH-dependence, and the effect of pH on arsenic sorption differs between arsenate and arsenite. Arsenate adsorption decreases consistently with increasing pH; whereas arsenite adsorption initially increases with pH to a sorption maximum at pH 7-9, where after sorption decreases with further increases in pH. Results indicate that competitive adsorption between silicic acid and arsenate is negligible under the experimental conditions; whereas strong competitive adsorption was observed between silicic acid and arsenite, particularly at low and high pH. In-situ, flow-through ATR-FTIR data reveal that in the absence of silicic acid, arsenate forms inner-sphere, binuclear bidentate, complexes at the ferrihydrite surface across the entire pH range. Silicic acid also forms inner-sphere complexes at ferrihydrite surfaces throughout the entire pH range probed by this study (pH 2.8 - 9.0). The ATR-FTIR data also reveal that silicic acid undergoes polymerization at the ferrihydrite surface under the environmentally-relevant concentrations studied (e.g., 1.0 mM). According to ATR-FTIR data, arsenate complexation mode was not affected by the presence of silicic acid. EXAFS analyses and DFT modeling confirmed that arsenate tetrahedra were bonded to Fe metal centers via binuclear bidentate complexation with average As(V)-Fe bond distance of 3.27 Å. The EXAFS data indicate that arsenite forms both mononuclear bidentate and binuclear bidentate complexes with 6-L ferrihydrite as indicated by two As(III)-Fe bond distances of ~2.92-2.94 and 3.41-3.44 Å, respectively. The As-Fe bond distances in both arsenate and arsenite EXAFS spectra remained unchanged in the presence of Si, suggesting that whereas Si diminishes arsenite adsorption preferentially, it has a negligible effect on As-Fe bonding mechanisms.

    更新日期:2019-11-01
  • TRANSPORT AND FATE OF AMMONIUM AND ITS IMPACT ON URANIUM AND OTHER TRACE ELEMENTS AT A FORMER URANIUM MILL TAILING SITE.
    Appl. Geochem. (IF 2.894) Pub Date : 2013-12-21
    Ziheng Miao,Hakan Nihat,Andrew Lee McMillan,Mark L Brusseau

    The remediation of ammonium-containing groundwater discharged from uranium mill tailing sites is a difficult problem facing the mining industry. The Monument Valley site is a former uranium mining site in the southwest US with both ammonium and nitrate contamination of groundwater. In this study, samples collected from 14 selected wells were analyzed for major cations and anions, trace elements, and isotopic composition of ammonium and nitrate. In addition, geochemical data from the U.S. Department of Energy (DOE) database were analyzed. Results showing oxic redox conditions and correspondence of isotopic compositions of ammonium and nitrate confirmed the natural attenuation of ammonium via nitrification. Moreover, it was observed that ammonium concentration within the plume area is closely related to concentrations of uranium and a series of other trace elements including chromium, selenium, vanadium, iron, and manganese. It is hypothesized that ammonium-nitrate transformation processes influence the disposition of the trace elements through mediation of redox potential, pH, and possibly aqueous complexation and solid-phase sorption. Despite the generally relatively low concentrations of trace elements present in groundwater, their transport and fate may be influenced by remediation of ammonium or nitrate at the site.

    更新日期:2019-11-01
  • A rapid and precise procedure for Pb isotopes in whole blood by Fe co-precipitation and MC-ICPMS analysis.
    Appl. Geochem. (IF 2.894) Pub Date : 2005-04-01
    Steven N Chillrud,N Gary Hemming,James M Ross,Sean Wallace,Nancy Loiacono

    Elevated Pb levels in humans through environmental exposure are a significant health concern requiring scientific study of the sources of, and physiological response to this toxin. This requires a simple and precise method for measuring radiogenic Pb isotopes and Pb levels in blood. Presented here is a combination of methods for separation and analysis of Pb previously used predominantly for geologic samples. This includes separation of Pb from the complex matrix of blood samples using an Fe co-precipitation method, followed by isotopic analysis by multi-collector inductively coupled plasma mass spectrometry. Evaluation of the efficacy of this procedure shows that the precision of sample preparations as measured by % difference between the (207)Pb/(206)Pb of duplicate analyses averages 0.064% (n = 48). Using the same preparation and analysis techniques to measure Pb concentrations by isotope dilution resulted in a reproducibility of better than 6%. The method was successfully used to measure uptake of ingested soil Pb in a study of the bioavailability of Pb in contaminated soils.

    更新日期:2019-11-01
  • Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses.
    Appl. Geochem. (IF 2.894) Pub Date : 2010-02-18
    Sarah M Hayes,Scott A White,Thomas L Thompson,Raina M Maier,Jon Chorover

    Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5 to 8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and "bioavailable" metal concentrations result from associated variation in particle-scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 - 13 g kg(-1)) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4 - 6 g kg(-1)) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.

    更新日期:2019-11-01
  • Comparison of arsenic concentrations in simultaneously-collected groundwater and aquifer particles from Bangladesh, India, Vietnam, and Nepal.
    Appl. Geochem. (IF 2.894) Pub Date : 2009-11-04
    A van Geen,K Radloff,Z Aziz,Z Cheng,M R Huq,K M Ahmed,B Weinman,S Goodbred,H B Jung,Y Zheng,M Berg,P T K Trang,L Charlet,J Metral,D Tisserand,S Guillot,S Chakraborty,A P Gajurel,B N Upreti

    One of the reasons the processes resulting in As release to groundwater in southern Asia remain poorly understood is the high degree of spatial variability of physical and chemical properties in shallow aquifers. In an attempt to overcome this difficulty, a simple device that collects groundwater and sediment as a slurry from precisely the same interval was developed in Bangladesh. Recently published results from Bangladesh and India relying on the needle-sampler are augmented here with new data from 37 intervals of grey aquifer material of likely Holocene age in Vietnam and Nepal. A total of 145 samples of filtered groundwater ranging in depth from 3 to 36 m that were analyzed for As (1-1000 mug/L), Fe (0.01-40 mg/L), Mn (0.2-4 mg/L) and S (0.04-14 mg/L) are compared. The P-extractable (0.01-36 mg/kg) and HCl-extractable As (0.04-36 mg/kg) content of the particulate phase was determined in the same suite of samples, in addition to Fe(II)/Fe ratios (0.2-1.0) in the acid-leachable fraction of the particulate phase. Needle-sampler data from Bangladesh indicated a relationship between dissolved As in groundwater and P-extractable As in the particulate phase that was interpreted as an indication of adsorptive equilibrium, under sufficiently reducing conditions, across 3 orders of magnitude in concentrations according to a distribution coefficient of 4 mL/g. The more recent observations from India, Vietnam and Nepal show groundwater As concentrations that are often an order of magnitude lower at a given level of P-extractable As compared to Bangladesh, even if only the subset of particularly reducing intervals characterized by leachable Fe(II)/Fe >0.5 and dissolved Fe >0.2 mg/L are considered. Without attempting to explain why As appears to be particularly mobile in reducing aquifers of Bangladesh compared to the other regions, the consequences of increasing the distribution coefficient for As between the particulate and dissolved phase to 40 mL/g for the flushing of shallow aquifers of their initial As content are explored.

    更新日期:2019-11-01
  • Considerations for conducting incubations to study the mechanisms of As release in reducing groundwater aquifers.
    Appl. Geochem. (IF 2.894) Pub Date : 2009-11-04
    Kathleen A Radloff,Anya R Manning,Brian Mailloux,Yan Zheng,M Moshiur Rahman,M Rezaul Huq,Kazi M Ahmed,Alexander van Geen

    Microbial Fe reduction is widely believed to be the primary mechanism of As release from aquifer sands in Bangladesh, but alternative explanations have been proposed. Long-term incubation studies using natural aquifer material are one way to address such divergent views. This study addresses two issues related to this approach: (1) the need for suitable abiotic controls and (2) the spatial variability of the composition of aquifer sands. Four sterilization techniques were examined using orange-colored Pleistocene sediment from Bangladesh and artificial groundwater over 8 months. Acetate (10 mM) was added to sacrificial vials before sterilization using either (1) 25 kGy of gamma irradiation, (2) three 1-h autoclave cycles, (3) a single addition of an antibiotic mixture at 1x or (4) 10x the typical dose, and (5) a 10 mM addition of azide. The effectiveness of sterilization was evaluated using two indicators of microbial Fe reduction, changes in diffuse spectral reflectance and leachable Fe(II)/Fe ratios, as well as changes in P-extractable As concentrations in the solid phase. A low dose of antibiotics was ineffective after 70 days, whereas autoclaving significantly altered groundwater composition. Gamma irradiation, a high dose of antibiotics, and azide were effective for the duration of the experiment.

    更新日期:2019-11-01
  • Mechanism of Hg(II) Immobilization in Sediments by Sulfate-Cement Amendment.
    Appl. Geochem. (IF 2.894) Pub Date : 2016-03-22
    Susana Serrano,Dimitri Vlassopoulos,Peggy A O'Day

    Reactive amendments such as Portland and super-sulfate cements offer a promising technology for immobilizing metalloid contaminants such as mercury (Hg) in soils and sediments through sequestration in less bioavailable solid forms. Tidal marsh sediments were reacted with dissolved Hg(II) in synthetic seawater and fresh water solutions, treated with Portland cement and FeSO4 amendment, and aged for up to 90 days. Reacted solids were analyzed with bulk sequential extraction methods and characterized by powder X-ray diffraction (XRD), electron microscopy, and synchrotron X-ray absorption spectroscopy at the Hg LIII- and S K-edge. In amended sediments, XRD, SEM and sulfur K-edge XANES indicated formation of gypsum in seawater experiments or ettringite-type (Ca6Al2(SO4)3(OH)12.26H2O) phases in fresh water experiments, depending on the final solution pH (seawater ∼8.5; freshwater ∼10.5). Analysis of Hg EXAFS spectra showed Cl and Hg ligands in the first- and second-coordination shells at distances characteristic of a polynuclear chloromercury(II) salt, perhaps as a nanoparticulate phase, in both seawater and fresh water experiments. In addition to the chloromercury species, a smaller fraction (∼20-25%) of Hg was bonded to O atoms in fresh water sample spectra, suggesting the presence of a minor sorbed Hg fraction. In the absence of amendment treatment, Hg sorption and resistance to extraction can be accounted for by relatively strong binding by reduced S species present in the marsh sediment detected by S XANES. Thermodynamic calculations predict stable aqueous Hg-Cl species at seawater final pH, but higher final pH in fresh water favors aqueous Hg-hydroxide species. The difference in Hg coordination between aqueous and solid phases suggests that the initial Hg-Cl coordination was stabilized in the cement hydration products and did not re-equilibrate with the bulk solution with aging. Collectively, results suggest physical encapsulation of Hg as a polynuclear chloromercury(II) salt as the primary immobilization mechanism.

    更新日期:2019-11-01
  • Chemical Treatments for Mobilizing Arsenic from Contaminated Aquifer Solids to Accelerate Remediation.
    Appl. Geochem. (IF 2.894) Pub Date : 2010-11-16
    Karen Wovkulich,Brian J Mailloux,Allison Lacko,Alison R Keimowitz,Martin Stute,H James Simpson,Steven N Chillrud

    Arsenic is a prevalent contaminant at US Superfund sites where remediation by pump and treat systems is often complicated by slow desorption of As from Fe and Al (hydr)oxides in aquifer solids. Chemical amendments that either compete with As for sorption sites or dissolve Fe and Al (hydr)oxides can increase As mobility and improve pump and treat remediation efficiency. The goal of this work was to determine optimal amendments for improving pump and treat at As contaminated sites such as the Vineland Chemical Co. Superfund site in southern New Jersey. Extraction and column experiments were performed using As contaminated aquifer solids (81 ± 1 mg/kg), site groundwater, and either phosphate (NaH(2)PO(4)·H(2)O) or oxalic acid (C(2)H(2)O(4)·2H(2)O). In extraction experiments, phosphate mobilized between 11% and 94% of As from the aquifer solids depending on phosphate concentration and extraction time (1 mM-1 M; 1-24 h) and oxalic acid mobilized between 38 and 102% depending on oxalic acid concentration and extraction time (1-400 mM; 1-24 h). In column experiments, phosphate additions induced more As mobilization in the first few pore volumes but oxalic acid was more effective at mobilizing As overall and at lower amendment concentrations. At the end of the laboratory column experiments, 48% of As had been mobilized from the aquifer sediments with 100 mM phosphate and 88% had been mobilized with 10 mM oxalic acid compared with 5% with ambient groundwater alone. Furthermore, simple extrapolations based on pore volumes suggest that chemical treatments could lower the time necessary for clean up at the Vineland site from 600 a with ambient groundwater alone to potentially as little as 4 a with 10 mM oxalic acid.

    更新日期:2019-11-01
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