The research on the sorption properties of the X-ray amorphous silica foam
Introduction
The prevention of surface water and groundwater pollution and aquatic ecosystem restoration are currently the priority tasks for protecting the environment. The contaminated water objects cleaning problem solution is associated with new sorbent development, including highly effective oil and petroleum product sorbents for oily wastewater purification and elimination of the oil spill effects. Various materials of both natural and artificial origin are used to obtain different types of oil sorbents (Asadpour et al., 2013, Rotar et al., 2014). Plant-waste sorbents, synthetic (polyethylene, polypropylene) sorbents, carbon sorbents, porous aluminosilicate material (perlite, vermiculite, expanded clay) sorbents, etc. are successfully used. Inorganic sorbents of natural and artificial origin have a set of properties: high absorption capacity, chemical, and thermal stability, environmental safety, low cost. And in terms of regeneration possibility, preference is given to inorganic sorbents compared with organic natural or synthetic materials.
The comparative oil content, sorption rate, porous structure nature, reusing, and recycling possibility analysis of various sorption materials are given in Asadpour et al., 2013, Cortez et al., 2016, Patalano et al., 2019, Bandura et al., 2017. The authors showed that oil receptivity and hydrophobicity are the main qualitative characteristics of oil sorbents.
Many natural, inorganic, and synthetic aluminosilicates are capable of attracting oil selectively but do not always meet the required criteria for oil capacity, as well as the ability to retain petroleum products. The oleophilic and hydrophobic properties of such materials can be improved by applying various methods of modifying their surface. Well-known methods for aluminosilicate processing differ in the type of modifying substances and their aggregation state. Monomolecular hydrophobic layers or thin hydrophobic films are obtained by processing the material with solutions, emulsions, or substance vapors that weakly interact with water, but are firmly held to the surface.
For example, vermiculite can be an object for modification because it swells easily in water and many organic liquids due to crystal lattice defects. As a result, it cannot be used as an oil sorbent in its pure form. To obtain unsinkable hydrophobic oil sorbents, the surface modification of thermally activated vermiculite was studied in Gubkina et al. (2011). Organosilicon compounds (organosiloxanes) based on water and organic solvents (white spirit, ethanol) were chosen as hydrophobizators. The hydrophobization process was conducted in the liquid phase. The hydrophobizer emulsion was combined with vermiculite, mixed thoroughly, kept for 15 min, and then dried for 48 h until full hydrophobic effect.
The research (Fokina, 2019) on the effectiveness of using modified hydrophobic vermiculite for petroleum products purification showed that processing of thermally activated vermiculite with oligo-methyl-siloxane (non-alkaline organosilicon compound) allows obtaining a non-toxic sorbent with high water resistance and long-term ability to stay on the water surface. Sorbents based on vermiculite can be burned, modified, and reused after application in the purification process.
The authors of Shapkin et al. (2019) obtain a hydrophobic coating on expanded vermiculite by processing it with a 2%–5% solution of polyethylene terephthalate in chloroacetic acid or a 5%–10% solution of polyurethane in a polar organic solvent (acetone, ethyl acetate, diethyl ether, etc.). The processing is carried out under normal conditions, mixing the mixture until a hydrophobic film is formed not only on the external but also on the inner surface of the processed material pores until polymer content in the sorbent consisting of 2%–5% by carbon is reached. Plastic bottles can also be used as polymers. The resulted sorbent has a contact angle of at least 130 on the grain surface, a specific surface area of 80–90 m2/g, and high oil content.
Another object for modification is the layered montmorillonite silicate that has prominent sorption properties and, due to its structure, can swell strongly. The authors of Park et al. (2008) studied the montmorillonite hexadecyltrimethylammonium (HDTMA) surface modification method. The main principle of the method is cation replacement on the surface of natural montmorillonite with organic HDTMA cations in its aqueous solution.
The results of studying the sorption ability of expanded perlite after modifying its surface with the synthetic polymeric materials (polyvinyl acetate and polyvinyl chloride) are presented in Vardanyan (2017). The optimal modification conditions for fixing polymer molecules on the perlite surface were experimentally determined by the authors. The perlite surface was processed with an activator solution (monochloramine HB) in ethyl acetate. Then the material was saturated with a modifier in the form of solutions in a binary mixture of solvents (cyclohexanone–toluene in a ratio of 1:3). Perlite gains hydrophobic properties after drying. As a result, sorption capacity concerning petroleum products under static conditions increased by 20%–40%.
The described hydrophobic coating formation methods (Fokina, 2019, Gubkina et al., 2011, Park et al., 2008, Vardanyan, 2017, Shapkin et al., 2019) are based on the processing of aluminosilicate materials in a liquid phase, that is, the application of a modifier solution on the surface of the particles, followed by solvent removal during the drying process. However, it is difficult to avoid particle agglomeration in the case of dispersed material surface processing with modifier solutions. Processing of modifying substances in the vapor–gas phase or a gaseous medium opens up a possibility of producing sorbents based on fine materials using a wide range of modifiers.
The research results of expanded perlite surface modification by the method of plasma-chemical vapor deposition are presented by the authors of Gürsoy and Karaman (2016). A rotary plasma reactor is used for efficient mixing. The material acquires super-hydrophobicity as a result of thin polymer film formation. The morphology of perlite particles does not change after modification. However, the technology proposed by the authors requires expensive equipment to use that complicates and increases the cost of its implementation.
Another example of obtaining a sorbent based on vermiculite is described in Mesyats and Ostapenko (2009). The authors suggest vermiculite firing and processing with hydrocarbons of petroleum origin (diesel fuel, marine fuel oil, engine oil, kerosene, paraffin) simultaneously in a stream of hot gases generated during fuel combustion in a nozzle torch. The result is a carbon-containing sorbent with a carbon content of 0.7–1.1% that has a hydrophobic nanolayer on the surface. The obtained sorbent has ion-exchange activity and significant oil capacity that allows using of it for the purification of water from multicomponent pollution. Vermiculite firing in a gas stream will be effective for light and fine fractions because the quality of the resulted sorbent will deteriorate during vermiculite of large fraction processing. Also, it is necessary to use nozzle devices and a compressor for compressed air production to obtain a flow of coolant and hydrophobic gas.
Well-known oil sorbents are not versatile and have certain disadvantages or use specifications associated with their production, operating conditions, recycling, or regeneration. Obviously, the development of technologies for producing sorbents and the new materials with sorption properties creation remains relevant today.
At this point, new materials obtained as a result of processing technogenic, ore, and non-metallic raw materials are interesting for specialists. Considerable amounts of such raw materials are formed at heat, iron and steel plants, and mining and processing plants. Research in the field of industrial waste processing is actively carried out all over the world these days. Extraction of valuable compounds from technogenic raw materials, including rare metals and trace elements (Potapov et al., 2003, Shpirt, 2012), aluminosilicate microspheres, and other components are of particular interest, as well as resolving the environmental issues (Potapov and Pinchuk, 2002, Pinchuk et al., 2019).
A large number of scientific publications and patents are dedicated to the research on processing technologies for various recyclable materials (metallurgical and fuel slags, fly ash at thermal power stations, ore preparation tailings, etc.) to produce foam-glass-crystalline materials (Ponsot and Bernardo, 2013, Guo et al., 2010, Fernandes et al., 2009, Wu et al., 2006, Zhu et al., 2016, Ding et al., 2015).
In Suvorova and Manakova (2017), optimal technological conditions were determined for the production of foam-glass-crystalline sound and heat insulation with the fine-porous structure using preparation tailings of apatite–nepheline ores and glass waste. The authors of Portnyagin et al. (2011) have studied the properties of foam glass materials obtained from cullet and high calcium slag compositions as a result of brown coal combustion. The bulk density of the obtained granular foam glass is 180–200 kg/m3. The compressive strength in the cylinder is 1.0–1.1 MPa.
The fundamental possibility of producing foam glass materials using ash and slag waste from burning coal as a component of the burden at Tomsk regional power station is shown in Kazmina et al. (2011). The compositions of the initial burdens and their heat processing modes are determined. The obtained samples of foam-glass-crystalline materials are characterized by a high degree of pore structure homogeneity with a pore size of 1.1 mm and an interpore partition of 53 m that allows them to obtain a material with a density of not more than 370 kg/m3. Despite the high degree of obtained material pore structure homogeneity, the chemical inhomogeneity of different batches is a disadvantage.
The physical and mechanical properties and the foam glass macrostructure can be changed by introducing modifying additives into the foaming mixture composition. Consequently, the positive effect of small (up to 1 wt%) titanium concentrate additives on the foam glass mechanical properties was obtained in Kazmina et al. (2014). It should be noted that this effect is associated with a change in its macrostructure due to the polymodal distribution of small pores followed by a change in the composition of the interstitial septum amorphous matrix.
The Siberian Branch of the Russian Academy of Sciences is researching the development of non-waste technologies for processing mineral raw materials using the reductive melting method (Ivanov and Pavlov, 2013) with separation of the molten material into a silicate of stable chemical composition and metal parts. The aim is to solve environmental issues associated with the accumulation of industrial waste and low-grade crude ore. As a result of molten material silicate part porosity in the thermal shock mode, they obtained a new product — silica foam. A versatile waste-free processing complex for technogenic, ore and non-metallic materials has been developed. The technology foundations and the results of comprehensive research on the silica foam properties are described in the research (Pavlov, 2005). A distinctive feature of the developed technology is the ability to use various aluminosilicate materials for obtaining highly porous materials. According to the authors of Proshkin et al. (2002), about 10 m3 of stable silica foam is formed from 1 tone of technogenic raw materials.
Silica foam is mainly used as an effective building material, for example, for noise and heat insulation (Proshkin et al., 2002, Yatsenko et al., 2010, Soktoyeva et al., 2018). Several research projects are dedicated to the research on the possibility of obtaining refractory structural foam ceramic or heat insulation based on silica foam (Melkonyan et al., 2016, Pavlov and Shabanov, 2003). The authors of the research (Shabanov et al., 2002b) developed the method and demonstrated the prospects of obtaining synthetic -wollastonite based on silica foam. It was shown in Petrakovskaya et al. (2001) that silica foam can be used as a filtering material since it has an absorption capacity towards aggressive gaseous emissions of fluorine, arsenic, hydrogen sulfide, carbon disulfide, and nitrogen oxides. Foam silicate filters have been successfully tested to absorb harmful emissions of hydrogen fluoride in the gas path of aluminum production.
First of all, interest in the research on silica foam materials that do not contain harmful impurities after high-temperature processing is explained by their unique properties and environmental safety.
The physical and mechanical, thermal, and physical properties of silica foam, its structural properties, high porosity, and presence of open pores of various sizes developed system make it possible to consider silica foam as a promising raw material for the development of new sorbents for oil and petroleum products.
Section snippets
Aim and purposes of the research
The main aim of this research is to study the properties of granular silica foam obtained from mica shale ore for oleophilic sorbent production.
To achieve this goal, the following tasks were accomplished:
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development and experimental verification of the method of granular silica foam modification in hydrocarbon gas–vapor phase
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development of changes in the silica foam porous structure during modification,
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analysis of the modified silica foam properties, including its sorption ability concerning
Silica foam samples
Samples of silica foam marked S1 and S2 obtained from waste of mica shale ore were chosen as objects of the research.
Silica foam was obtained from the processing of mica shale ore waste with limestone grinding in a universal complex for technogenic raw material processing. Its appearance is shown in Fig. 1.
The technology developed by the authors (Ivanov and Pavlov, 2013) includes burden melting in a bubbling molten slag with separation of the process into a molten material zone and a deep
Results and discussion
A series of experiments with variations in the calcination temperature from 200 to 450 °C was carried out to select the technological regimes for processing the silica foam. The heating temperature for modifying coating applying is from 360 to 550 °C, the vacuum level is from 60 to 98 kPa and the modifying substance flow rate is from 0.5 to 2.0% by silica foam weight. M-100 mazut (fuel oil) grade (the analog is MDO; ISO 8217:2017) and highly refined P-2 paraffin oil grade (the analog is NF MP:
Conclusions
The experiments demonstrated that silica foam obtained as a product of the ore wastes processing (ore of mica shale) is subjected to thermochemical modification in the developed pilot unit, the optimal modification conditions were experimentally determined.
The research results of the structural properties of the silica foam indicate a developed porous structure with open and closed pores of various sizes. Silica foam processing during modification to the temperature of 550 °C does not affect
CRediT authorship contribution statement
O.N. Tsybulskaya: Investigation, Data curation, Formal analysis, Writing - review & editing, Visualization. T.V. Ksenik: Investigation, Data curation, Validation. A.A. Yudakov: Project administration, Supervision, Conceptualization, Methodology, Investigation, Data curation, Formal analysis, Writing - original draft. M.V. Pavlov: Investigation, Data curation, Resources. V.F. Pavlov: Investigation, Data curation.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The work is supported by the Ministry of Science and Higher Education of the Russian Federation (Decree #P218, Agreement #02.G25.31.0166 (075-11-2018-009) on 01.12.2015 between Joint-stock company «Far Eastern plant «Zvezda» and Ministry of Science and Higher Education of the Russian Federation).
The authors are grateful to A.A. Kisel, the Principal Industrial Engineer at the Engineering and Technology Center of the Institute of Chemistry of the Far Eastern Branch of the Russian Academy of
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