Elsevier

Hydrometallurgy

Volume 219, May 2023, 106084
Hydrometallurgy

Microbiological passive treatment of Mn/Zn-containing mine water

https://doi.org/10.1016/j.hydromet.2023.106084Get rights and content

Highlights

  • Mn/Zn-containing mine waters effectively treated by two passive tank systems.

  • >99% metals removed from 70 mg/L Mn2+ and 2 mg/L Zn2+ in both tanks.

  • Operation possible at HRT 8–15 h (Tank-I) and HRT 17 h (Tank-II).

  • Different mineralogy and microbial activity/diversity observed in two tanks.

  • Stability of the resulting Mn oxides was comparable in two tanks.

Abstract

The Mn/Zn-containing black sediments were formed at the closed N-mine site and used as a common inoculant to set up two different laboratory-scale passive bioprocesses (named Tank-I and Tank-II) to treat mine waters containing 70 mg/L Mn2+ and < 1.8 mg/L Zn2+. Using CO32−-free synthetic mine water, Tank-I (a natural zeolite down-flow tank with surface aeration) achieved >97% Mn2+ and > 80% Zn2+ removal at an hydraulic retention time (HRT) of 15–17 h, while Tank-II (an up-flow tank filled with semi-calcined dolomite with a bottom aeration) removed >87% Mn and > 79% Zn at an HRT of 24 h. Further shortening of the HRT resulted in a rapid decline in performance (Zn2+ desorption followed by Mn2+ elution) in both tanks. As the semi-calcined dolomite in Tank-II had been passivated and deactivated during the pre-run period, periodic CaCO3 addition (plus HRT readjustment) was required in both tanks to reverse this performance degradation. Treatment of the real mine water was generally faster and more complete, presumably due to the continuous influx of naturally occurring CO32− into the system. This allowed for >99% Mn/Zn removal at HRT 8–15 h in Tank-I and at HRT 17 h in Tank-II. In Tank-I, birnessite was formed as a result of the oxidative removal of Mn2+ where the Mn average oxidation state (AOS) progressed from 3.53 to 3.85 through the activity of potential Mn-oxidizing genera such as Bacillus, Pseudonocardia, Brevibacillus, Nitrospira, Methylobacterium, Bosea, Leptothrix, Mycobacterium, Rhizobium and Pseudomonas. While in Tank-II, in addition to abiotic Mn removal by semi-calcined dolomite in the early stages, microbial Mn oxidation activity developed over time to produce woodruffite and birnessite, with Mn AOS progressing from 3.53 to 3.79 through the activity of potential Mn-oxidizing genera such as Methylobacterium and Leptothrix. The microbial community developed very differently between the two tanks, due to the different tank designs. Off-site Pseudomonas SK3 cells co-inoculated only in Tank-I were eliminated by the indigenous community, presumably due to the lack of Zn2+ tolerance. Both tanks were effective in treating the target mine water to meet the effluent standard while producing equally stable Mn oxides. Although the two tanks cannot be directly compared in detail due to their completely different designs, the simpler Tank-I design was superior overall in terms of speed and microbial activity and diversity.

Introduction

Among a variety of heavy metals contaminated in mining-impacted waters, soluble Mn (Mn2+) is particularly stable over a wide pH-Eh range, making its removal challenging. Although Mn is an essential trace element in biological systems, its excessive concentrations in water can cause a serious neurological disorder known as manganism (Santamaria and Sulsky, 2010). Therefore, many countries have set limits for Mn in water bodies (e.g., effluent standard 10 mg/L, drinking water standard 0.05 mg/L in Japan). The general active treatment approach to remove Mn is the chemical oxidation of Mn2+ to dark-brown precipitates of MnIII, IV-oxides at alkaline pHs. Since mine waters are often acidic, this conventional chemical oxidation approach requires a large input of neutralizing agents and can become costly.

On the other hand, microbial Mn oxidation is catalyzed by enzymatic activities, that can overcome the thermodynamic barrier to oxidize Mn at circumneutral or even weakly acidic pHs, where chemical Mn oxidation barely proceeds (Maynard, 2014; Bohu et al., 2016; Tebo et al., 2004; Tebo et al., 2005). Bacterial Mn2+ oxidation is typically catalyzed by multicopper oxidase enzymes via two sequential electron transfers, Mn2+ → MnIII-oxides → Mn IV-oxides (Tebo et al., 2004), and follows the stoichiometry of the chemical reaction as [1];Mn2++1/2O2+H2OMnIII,IVO2+2H+

At the same time, abiotic Mn oxido-reduction can take place via the disproportionation (favoring pH < 9) [2] and comproportionation (favoring alkaline pH) [3] reactions (Tebo et al., 2004; Takashima et al., 2012);2MnIIIsolidMnIVsolid+Mn2+Mn2++MnIVsolid2MnIIIsolid

Harnessing such microbial Mn oxidation capabilities could, therefore enable the development of alternative passive treatment processes, which would be beneficial from both economic and environmental perspectives.

Microbial Mn oxidation has been observed across diverse phylogenies in bacteria and fungi in both natural environments (marine and freshwater) and artificial structures (e.g., water treatment pipelines) (Okibe et al., 2013; Kitjanukit et al., 2019). The majority of Mn oxides found in natural, mild conditions are thought to be of biological origin, either directly via biogenic mineralization (typically as birnessite; (Na, Ca)0.5MnIII, IV2O4∙1.5H2O) or via the subsequent alteration of biogenic minerals (Bohu et al., 2016). Such microbial reactions are therefore expected to have a broad impact on Mn geochemistry. Mn-oxidizing bacteria reported to date include Firmicutes (Bacillus sp., Brevibacillus sp.), α-Proteobacteria (Pedomicrobium sp., Erythrobacter sp., Aurantimonas sp., Roseobacter sp. Rhizobium sp., Methylobacterium sp. Bosea sp.), β-Proteobacteria (Leptothrix sp., Sphaerotilus sp., Burkholderia sp.), γ-Proteobacteria (Pseudomonas sp., Oceanospirillum sp., Halomonas sp., Citrobacter sp., Pantoea sp.) and Actinobacteria (Arthrobacter sp., Pseudonocardia sp., Lapillicoccus sp., Leifsonia sp., Terrabacter sp., Mycobacterium sp.) (Bohu et al., 2016; Tebo et al., 2004; Sujith and Bharathi, 2011; Mariner et al., 2008; Kurt, 2019).

To date, bioprocesses for Mn removal have been investigated by various research groups, many of which have targeted groundwater and drinking water with Mn concentrations up to a few mg/L using sand biofilters. However, only a few studies have focused on the removal of high concentrations of Mn (tens of mg/L) from mine waters: e.g., Mao et al. (2022) treated acidic mine waters containing 60–100 mg/L Mn (pH 5.5) by a continuous stirred tank bioreactor at a hydraulic retention time (HRT) of 48 h, using a mixed microbial community enriched from the Mn-rich mine water. Representative species used in previous literature (as pure or mixed cultures) include Bacillus sp., Pseudomonas sp. and Leptothrix sp. (Cheng et al., 2017; Bai et al., 2016; Cai et al., 2014; Li et al., 2019; Hallberg and Johnson, 2005; Mao et al., 2022).

Biogenic Mn oxides such as birnessite are also known as adsorbents for a variety of divalent metals (i.e., Cu2+, Co2+, Mn2+, Zn2+, Cd2+, Pd2+), due to their large specific surface area with negatively-charged layered structure (Tebo et al., 2004). Tajima et al. (2022) carried out Zn2+ adsorption/co-precipitation tests using abiotic δ-MnO2 at neutral pHs (6.0 and 7.5) and found that triple-corner-sharing (TCS) inner-sphere complexation of Zn2+ on the δ-MnO2 surface was the dominant adsorption mechanism. As for the co-precipitation mechanism, the type of secondary minerals formed on the δ-MnO2 surface was controlled by the pH and Zn/Mn molar ratio. The authors concluded the importance of Mn-oxidizing bacteria to control the Mn2+ oxidation rate for the Zn2+ removal at neutral pHs, which would reduce the cost and environmental impact of AMD treatment.

Of the several thousand closed/abandoned metal mines that once operated in Japan during the industrialization period in the late 19th century, a few hundred mines still require measures (source control and/or water treatment) to prevent the contamination of the surrounding environment with toxic metals. To accelerate the technological shift towards more sustainable and economical water treatment, the Japanese Ministry of Economy, Trade and Industry (METI) is promoting further research and dissemination of passive mine water treatment systems.

This study focused on the case of N-mine, located in Japan, as one of several sites with Mn contamination in mine water. N-mine water contains a high concentration of Mn2+ (∼70 mg/L) as well as Zn2+ (<1.8 mg/L) and has been treated in a conventional active treatment plant since the mine was closed: The mine water from two mine adits (lower and higher adits) is pooled and forced-aerated (to remove dissolved carbonates) prior to alkalization (>pH 9) in a neutralization tank using slaked lime (Ca(OH)2). In order to explore the possibility of introducing a passive biological treatment system as an alternative, this study carried out laboratory-scale Mn oxidative removal tests using two different laboratory-scale water tanks filled with biologically active Mn sediments.

Section snippets

Characterization of water and sediment samples from the N-mine

Formation of brown and black sediment sludge was observed inside the lower and higher adits (Fig. 1a, b, respectively), and in cascade aeration tanks (Fig. 1c) constructed upstream of the confluence of the two watercourses. Brown and black sediments were collected separately from the interior of each adit. Mine water samples were collected at the confluence of the two watercourses from the lower and higher adits for determination of pH, Eh (vs. SHE), dissolved oxygen (DO), total organic carbon

Characterization of water and sediment samples from N-mine

In both the lower and higher adits, sediments with distinctive black or brown colors were visible (Fig. 1a, b). These sediments were collected and characterized separately. XRD analysis (Fig. 3) showed birnessite peaks for the black sediments from both the lower and higher adits, with the latter having slightly higher crystallinity (Fig. 3b, d), probably due to the less acidic pH (6.2) of the environment (Table 2). Both brown sediments showed broad peaks of ferrihydrite (FeIII2O3•0.5H2O) as

Conclusions

The utility of the passive bioprocess was investigated by designing two different continuous tank reactors to treat mine waters containing 70 mg/L Mn2+ and < 1.8 mg/L Zn2+. Tank-I (down-flow tank filled with natural zeolite with surface aeration; inoculated with the on-site Mn sediment plus off-site Pseudomonas cells): The CO32−-free synthetic mine water was effectively treated at a HRT of 15–17 h with ≥97% Mn2+ removal and ≥ 80% Zn2+ removal. Shorter HRT caused a rapid deterioration in

CRediT authorship contribution statement

Naoko Okibe: Conceptualization, Methodology, Resources, Writing – original draft, Writing – review & editing, Visualization, Supervision, Project administration, Funding acquisition. Kohei Nonaka: Investigation. Taiki Kondo: Investigation. Kazuhiko Shimada: Investigation. Peiyu Liu: Investigation.

Declaration of Competing Interest

The authors declare that there is no conflict of interest.

Acknowledgment

This study was funded by JOGMEC (Japan Organization for Metals and Energy Security), METI (Ministry of Economy, Trade and Industry) and JSPS KAKENHI Grand Number JP21K18922. The authors thank Yoshizawa Lime Industry Co., Ltd. and Shinsei Corporation for kindly providing semi-calcined dolomite and natural zeolite, respectively. The XAFS experiments were performed at Kyushu University Beamline (Saga-LS / BL06) with the proposal No. 2022IIK004 and 2022IIIK010.

References (28)

  • B.M. Tebo et al.

    Geomicrobiology of manganese(II) oxidation

    Trends Microbiol.

    (2005)
  • B. Alexandra et al.

    Sorption of copper and zinc by goethite and hematite

    Arch. Tech. Sci.

    (2015)
  • T. Bohu et al.

    Biological low-pH Mn(II) oxidation in a manganese deposit influenced by metal-rich groundwater

    Appl. Environ. Microbiol.

    (2016)
  • B.L. Bourre et al.

    Manganese removal processes and geochemical behavior in residues from passive treatment of mine drainage

    Chemosphere

    (2020)
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