Arsenic Precipitates Research Articles

Hydrometallurgical technologies of processing arsenic raw materials

Methods presented in Russian and foreign scientific literature sources for processing high-arsenic copper raw materials to convert arsenic into low-soluble and stable compounds are reviewed. Hydrometallurgical processing methods are shown to be applicable for converting environmentally hazardous components into inert solid wastes while avoiding the formation of gaseous emissions. The isolation of arsenic when processing raw materials involves its oxidation and precipitation in the form of low-soluble and stable compounds. Methods for arsenic oxidation using oxygen, hydrogen peroxide, ozone, mixture of oxygen and sulphur dioxide, sodium hypochlorite are compared. Methods of oxidation by iron and permanganate ions, bacteria (biooxidation), as well as by introducing an activated carbon catalyst, are also considered. Precipitation approaches include neutralization by lime, precipitation of sulphides, co-precipitation of arsenic with iron ions, precipitation of scorodite, and encapsulation technology. As a result of the performed analysis, the authors present a promising approach for solving the problem of processing high-arsenic copper concentrates to comply with standards governing arsenic emissions into the environment, including the comprehensive processing of these raw materials using autoclave oxidation. In addition to the ensuring effective precipitation of arsenic in the form of a low-toxic compound (scorodite), this method can be used to isolate valuable components (copper, gold, silver) with their subsequent extraction into individual finished products. The obtained results establish a direction for a further in-depth study of the problem.

Arsenic Precipitation in Heavily Arsenic‐Doped Czochralski Silicon

Heavily arsenic‐doped Czochralski (HAs‐CZ) silicon is an important substrate material for manufacturing power electronic devices. The arsenic impurities may be in a supersaturated status in a certain temperature range during the HAs‐CZ silicon crystal growth or the device fabrication. Then, whether and how the arsenic impurities can precipitate in HAs‐CZ silicon is an intriguing and practically significant issue that has never been addressed. Herein, it is first found that arsenic precipitation can occur in HAs‐CZ silicon when subjected to appropriately prolonged anneals at 550–950 °C. The resulting second‐phase precipitates are confirmed to be of orthorhombic SiAs phase, with the lattice parameters of a = 7.12 Å, b = 9.11 Å, and c = 9.00 Å, through systematic transmission electron microscopy characterizations. Moreover, it is discovered that the presence of vacancies/interstitial silicon atoms in HAs‐CZ silicon promotes/inhibits arsenic precipitation.

Optimization of Arsenic Fixation in the Pressure Oxidation of Arsenopyrite Using Response Surface Methodology

ABSTRACT Arsenic is a common pollutant and impurity present in complex gold ores. In the pressure oxidation (POX) of refractory gold-bearing sulfides, a major environmental challenge is the treatment of the hazardous waste released from arsenic-bearing minerals during processing. While the bulk removal of arsenic from solution can occur during POX, the formation of stable arsenates relies on the operating conditions during POX and the subsequent curing stage. Herein, response surface methodology (RSM) and central composite design have been investigated as viable approaches for optimizing arsenic fixation during the curing of the POX product of arsenopyrite. Curing time (0–24 h) and temperature (60–120°C) were examined as the model variables for RSM optimization, and the performance was assessed via arsenic and iron precipitation, along with the change in free acid and sulfate concentrations. Experimental validation of the optimized model conditions demonstrated good agreement with the simulated outputs and provided a 10% increase in arsenic removal over the best model input. The formation of basic ferric arsenate sulfate and scorodite under these conditions was supported by RSM and confirmed via characterization. In the investigated system, the maximum arsenic removal occurs at a critical threshold temperature of 107°C, over which the scorodite formation decreases with temperature. Thermodynamic modeling revealed the preferable formation of soluble FeHAsO4 + complexes over scorodite above this threshold temperature, decreasing arsenic fixation at higher temperatures.

An innovative strategy for efficient and economical arsenic removal in hydrometallurgical waste sulfuric acid by co-treatment with Fe–As coprecipitation residue via scorodite formation

Hydrometallurgical iron-arsenic (Fe–As) coprecipitation residue (FACR), a massive industrial solid waste, is a potentially cheapest Fe(III) source for the removal and fixation of As in waste sulfuric acid (WSA) as stable scorodite. This study innovatively proposed a method by controlling a low supersaturation degree of ferric arsenate in WSA via stepwise addition and slow dissolution of FACR, ensuring continuous ferric arsenate precipitation and scorodite crystallization. The results showed that As removal efficiency in WSA reached 99.92%. The decrease in the weight of solid waste was up to 37.1%. X-ray diffraction and infrared spectroscopy results indicated that scorodite is the principal crystalline As mineral in the products. The solid products displayed excellent stability with the TCLP concentrations of leached As and divalent metals (CuII, PbII, ZnII, and CdII) far below the US-EPA regulatory limits. Scanning/Transmission electron microscopy and X-ray photoelectron spectroscopy results revealed that such high TCLP stability could be ascribed to the adsorption of As and trace divalent metals on the raw/secondary Fe-(oxy)hydroxide minerals, such as FeO(OH), goethite, and ferrihydrite. This work provides an economical and efficient method for simultaneous treatment of WSA and FACR, which can support the sustainable development of the hydrometallurgical industry.

The effect of curing on arsenic precipitation and kinetic study of pressure oxidation of pyrite and arsenopyrite

In the treatment of arsenic-bearing refractory gold ores, pressure oxidation (POX) represents an attractive approach to arsenic immobilisation, as the conditions are suitable for both sulfide oxidation and the formation of stable arsenates. While extensive work has been conducted on the reactions of the arsenic species during POX, research on the behaviour in the subsequent curing stage has been limited. The focus of this study is to explore the effect of curing time and temperature on the properties of the arsenic-bearing product following POX, using a synthetic mixture of pyrite and arsenopyrite.Basic ferric arsenate sulfate (Fe(AsO4)1−x(SO4)x(OH)x.(1 − x)H2O) was observed as the major arsenic-bearing phase for Fe:As feeds of 1:1 and 2:1, and an increase in curing time resulted in higher arsenate stability based on characteristic leaching studies. A transformation to scorodite occurred for the 1:1 sample after 18–24 h of curing at 90–120 °C, along with a 60% increase in arsenic removal from solution and increased stability during characteristic leaching. Scorodite was absent at curing temperatures of 60 °C and for samples with a feed Fe:As above 2:1. At a feed Fe:As of 10:1, the major arsenic-bearing phases were amorphous iron arsenates, and arsenic concentrations in the leach extract were two orders of magnitude higher than 1:1 samples. Worryingly, this suggests that high arsenic-to-iron ratios are required for the formation of stable precipitates, with unstable phases forming otherwise.Oxygen consumption data collected during POX was used to fit a shrinking core model for pyrite and arsenopyrite, and the reaction of pyrite in this work followed a mixed control of chemical and oxygen transport, while that of arsenopyrite was limited by surface chemical reaction. Pyrite oxidation was enhanced by the presence of arsenopyrite, likely due to the formation of Fe(III)-As(V) complexes that contribute to mineral oxidation, and the magnitude of the enhancement increased with temperature.

Insight into the effect of SO42− on the precipitation and solubility of ferric arsenate in acidic solutions: Implication for arsenic mobility and fate

The effect of sulfate (SO42−) on the precipitation of As(V) and Fe(III) and the stability of the generated solid phase as well as its underlying mechanisms, which strongly influences the transportation and fate of As in acidic waters (such as acid mine drainage), is still not well known. This work systematically investigated the precipitation, decomposition, and settling properties of the ferric arsenate phase in the presence of different amount of SO42− at pH 1.2 and 1.8. The results showed that on the one side, the presence of SO42− delayed the removal of As and Fe from the aqueous phase and enhanced the solubility of solid ferric arsenate. The geochemical modelling results showed that the coexisting SO42− induced the formation of aqueous SO42−-Fe(III) complexes, inducing the decomposition of produced ferric arsenate solid phase. On the other side, the addition of SO42− promoted the growth rate of generated ferric arsenate and accelerated the settling of solids. The particle size distribution and transmission electron micorscopy analyses elucidated that the presence of SO42− significantly enlarged the ferric arsenate aggregate size. The infrared spectroscopy and S K-edge X-ray absorption near edge structure results proved that SO42− is incorporated into the structure of ferric arsenate by forming ferric arsenate sulfate solid solution, with each SO42− tetrahedron coordinating with approximately two FeO6 octahedra. The S K-edge extended X-ray absorption fine structrure result gave an averaged S-Fe interatomic distance of 3.21 Å. These results demonstrated that the presence of SO42− enlarged the aggregate size of ferric arsenate dominantly via the S-O-Fe bridging, and then accelerated the settling of SO4-ferric arsenate. The contrasting role of SO42− in influencing As obtained in this study is significant for understanding the mobilization and fate of As and the formation mechanisms of ferric arsenate minerals in acidic systems.

Removal Arsenic(V) Efficiency and Characteristics Using Modified Basic Oxygen Furnace Slag in Aqueous Solution

Basic oxygen furnace (BOF) slag, the solid waste produced in the steelmaking process, is reused in industry, agriculture and environmental treatment. However, as an adsorbent for wastewater, the removal effect of BOF slag on anionic pollutants needs to be improved. In this study, acid and alkali were used to modify BOF slag, and the removal efficiency and mechanism of arsenic(V) with modified BOF slag in solution were studied. The effects of the As(V) initial concentration, solution pH and reaction time on the removal efficiency were determined by batch experiments, and the removal mechanism of As(V) using modified BOF slag was studied by an adsorption kinetic model and isothermal adsorption model and the Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) spectral analysis. The results showed that the slag modified by 15% sulfuric acid had the best removal effect on As(V), while the removal effect of As(V) by alkali-modified slag was not ideal. The removal rate of As(V) by acid-modified slag increased with the increase in the initial concentration, decreased slowly with the increase in pH and reached equilibrium in 180 min. The adsorption kinetic model and isothermal adsorption model of As(V) by acid-modified BOF slag showed that the chemical adsorption was the limiting step. The FTIR and XPS analysis results showed that the silicate and ferrite in the acid-modified slag could remove As(V) in the solution by ion exchange to form an arsenate precipitate. Therefore, modified BOF slag can be used as a potential adsorbent for large scale arsenic polluted waterbody to realize the ecological utilization of industrial solid waste.

Impact of arsenic on phosphate solubilization, acquisition and poly-phosphate accumulation in endophytic fungus Serendipita indica

Symbiotic interactions play a crucial role in the phosphate (Pi) nutrient status of the host plant and offer resilience during biotic and abiotic stresses. Despite a competitive behavior of arsenic (AsV) with Pi, Serendipita indica association promotes plant growth by reducing arsenic bioavailability in the rhizosphere. Reduced arsenic availability is due to the adsorption, accumulation, and precipitation of arsenic in the fungus. The present investigation focused on the fitness and performance of Pi acquisition and utilization in S. indica for growth and metabolism under arsenic stress. The fungus accumulates a massive amount of arsenic up to 2459.3 ppm at a tolerable limit of arsenic supply (1 mM) with a bioaccumulation factor (BAF) 32. Arsenic induces Pi transporter expression to stimulate the arsenic acquisition in the fungus. At the same time, Pi accumulation was also enhanced by 112.2 times higher than the control with an increase in poly-P (polyphosphate) content (6.69 times) of the cell. This result suggests arsenic does not hamper poly-P storage in the cell but shows a marked delocalization of stored poly-P from the vacuoles. Furthermore, an enhanced exopolyphosphatase activity and poly-P storage during arsenic stress suggest induction of cellular machinery for the utilization of Pi is required to deal with arsenic toxicity and competition. However, at high arsenic supply (2.5 and 5 mM), 14.55 and 22.07 times reduced Pi utilization, respectively, was observed during the Pi uptake by the fungus. The reduction of Pi uptake reduces the cell growth and biomass due to competition between arsenic and phosphate. The study suggests no negative impact of arsenic on the Pi acquisition, storage, and metabolism in symbiotic fungus, S. indica, under environmental arsenic contamination.

PH-dependent structural changes of arsenic oxoacids in solution and solid phase: Raman spectrometry and computational studies

Reliably knowledge of the arsenic oxoacids in solution and solid-state and any possible relationship between them at different pHs is of concern in various scientific fields. This work compares the experimental Raman spectra of the inorganic arsenic oxoacids in aqueous solutions under acidic, neutral and alkaline conditions with the dry precipitates obtained from the corresponding aqueous solutions. Further, we explore the ability of quantum chemical methods to model the Raman spectra of the arsenic oxoacids in solution by considering explicit water molecules and conformational sampling, fitting reasonably well with the experimental spectra in the whole pH range covered. Hydrogen bridges and the coexistence of arsenic oxoacids facilitate strong overlapping in the Raman spectra of the As(III) aqueous samples compared with the As(V) ones. Some Raman shifts of the dry arsenic precipitates correlate well with the corresponding Raman spectra of the same arsenic species in aqueous solutions, allowing a practical use of the Raman spectrometry for indirect screening purposes of arsenic speciation in both condensed phases.

A Comprehensive Potentiometric Study of the Tartrate Complexes of Trivalent Arsenic, Antimony, and Bismuth in Aqueous Solution.

The tartrate complexes of trivalent arsenic, antimony, and bismuth were studied potentiometrically. The existing, fragmentary data on the antimony/l-(+)-tartrate system were confirmed. Nine complexes of arsenic and bismuth with optically active, racemic, and meso-tartrate, as well as complexes of antimony with meso-tartrate, were newly identified, and their formation constants computed. Difficulties arising from the poor stability of the arsenic complexes and precipitation in the Sb(III)/meso-tartrate system were overcome by titrating at very high concentrations [As(III) systems] and using an auxiliary ligand [Sb(III) in the presence of catechol]. All data were obtained at 25.0 °C and at constant ionic strength [0.1 mol L-1 for Sb(III) and Bi(III) complexes and 1 mol L-1 for As(III) complexes]. Speciation diagrams of all systems at millimolar concentrations were computed on the basis of the newly obtained constants and the results discussed.

Arsenic Trioxide Leaching and Scorodite Crystallization in Methanesulfonic Acid

ABSTRACT Arsenic, one of the most toxic elements, is a byproduct generated from metallurgical processes of arsenic-containing ores. Arsenic can be formed into an arsenic trioxide as a byproduct during the decopperization in electro-refining process when processing high arsenic-bearing copper minerals. However, arsenic trioxide has a very high arsenic mobility, so it requires to be re-dissolved and immobilized into scorodite (FeAsO4▪2H2O). In this study, methanesulfonic acid (MSA) was tested for both arsenic trioxide leaching and scorodite precipitation. Arsenic trioxide leaching tests showed the arsenic extraction of 80% at 21°C in MSA with H2O2 as an oxidant within 6 hours. Meanwhile, arsenic precipitation tests were conducted to achieve above 95% arsenic removal within 6 hours by the formation of scorodite at an initial pH of 0.5 and temperature of 80°C. In addition, coarser scorodite particles were formed in higher temperature and lower solution pH. The optimum condition for scorodite crystallization in MSA medium can be suggested to be at 80°C with the initial pH of 0.5.

A novel scheme for safe disposal and resource utilization of arsenic-alkali slag

As solid waste posing a great threat to the environmental system, the disposal of arsenic-alkali slag has become the top priority in the development of the antimony industry. In this paper, a novel technological scheme combining the advantages of chemical precipitation and fractional crystallization is proposed for the safe disposal and resource utilization of arsenic-alkali slag. The scheme is mainly composed of three parts, namely, leaching of arsenic-alkali slag, selective removal of arsenic in the arsenic-alkali solution, and evaporation crystallization of alkali solution. In the leaching part, the optimum leaching parameters are determined by orthogonal tests. In the arsenic and alkali separation part, based on thermodynamic analysis, the selective removal of arsenic from arsenic-alkali solution is realized by forming ammonium magnesium arsenate (MgNH4AsO4) precipitation. In the evaporation crystallization part, the crystalline product with sodium carbonate (Na2CO3) content of 89.87% is obtained by the evaporation crystallization experiment. The whole process does not produce secondary pollution and realizes the reuse of wastewater. The final products are leaching residue, arsenic slag, and sodium carbonate with an arsenic content of 0.83%, 24.93%, and 0.18%, respectively.

Simulation platform for in-situ Fe(II) oxidation and bioscorodite crystallization in a one-step process for As(V) immobilization from acid wastewater

Crystalline scorodite is considered one of the safest materials available for the removal and disposal of arsenic. Its formation by biological means represents a promising solution for the treatment of acidic wastewater containing arsenic. In this study, an analysis of the processes that take place in a bioreactor for the biogenic scorodite crystallization was performed using mathematical modeling. The model was fitted to a set of experimental data, including batch and continuous bioreactors using two different thermoacidophilic archaeal strains, showing a successful model prediction capability (0.85 < R2 < 0.97 with 0.001 < p-values for all variables). A parametric analysis showed that the arsenic precipitation rate constant (kAs(V)) was the parameter with no-statistically significant differences between treatments, being the least sensitive parameter. Our results suggest that the regulation of iron oxidation rate is a key factor in the arsenic precipitation process. Therefore, further experimental studies should be carried out in this field to improve reactor productivities. In addition, the model was implemented to simulate the effect of substrate affinity, cell concentration and iron/arsenic molar ratio on iron oxidation, arsenic precipitation, and crystal size, noting that these parameters are critical in process design due to their strong relationship with operating and recovery costs.

Red mud regulates arsenic fate at acidic pH via regulating arsenopyrite bio-oxidation and S, Fe, Al, Si speciation transformation

Red mud (RM) as waste of industrial aluminum production is piling up in huge ponds. RM could be a cost-effective adsorbent for heavy metals, but adsorption is vulnerable to pH changes, metal ions speciation and the occurrence of iron bearing minerals. In this study, the precipitation and elemental speciation transformation relevant to arsenic fate in responding to the addition of RM during arsenopyrite bio-oxidation by Sulfobacillus thermosulfidooxidans was investigated. The results show that the addition of RM significantly changed the arsenic precipitation and the solution chemistry and thus affected the arsenopyrite bio-oxidation and arsenic fate. An addition of a small amount (≤ 4 g/L) of RM substantially promoted arsenopyrite bio-oxidation with formation of SiO2 @ (As, Fe, Al, Si) spherical nanoparticles that can enhance the stability of the immobilized arsenic. The SiO2-based spherical nanoparticles precipitate was mainly composed of jarosites, amorphous ferric arsenate and crystalline scorodite, and its formation were controlled by Fe3+ concentration and solution pH. An addition of increased amount of RM (≥ 6 g/L) resulted in a significant increase of the solution pH and a decrease in the Fe2+ bio-oxidation activity, and spherical nanoparticles were not formed. Consequently, the dissolution of arsenopyrite was inhibited and the release of arsenic was blocked. This study suggests the applicability of RM in mitigation of arsenic pollution from bio-oxidation of As-bearing sulfide minerals.

Covellite (CuS) as a novel adsorbent for the direct removal of As(III) and As(V) simultaneously from groundwater

ABSTRACT Covellite (CuS) synthesized by precipitation method using sodium sulfide as the precipitant efficiently adsorbs As(III) and As(V) from water in 4–9 pH range. The adsorption does not require any pretreatment step for the oxidation of As(III) into As(V). The process of sorption entails the precipitation of copper arsenate, Cu3(AsO4)2, formed due to the reaction between As species and CuS, in the crystalline surface moiety of covellite. The existence of As(V) in the adsorbed state is ascertained chemically by exploiting the selective extraction of As(V) in aqueous and As(III) in nonpolar solvents. The conversion of As(III) to As(V) occurs by a disproportionation reaction induced by sulfhydryl group formed as a result of the protonation of S atoms of CuS in the aqueous medium. The process of adsorption is fast and the adsorption follows the Freundlich isotherm for both As species. Cu3(AsO4)2 is soluble in mild acidic solutions and its quantitative desorption is affected in <2.0 pH HCl. In column experiments, CuS (2 g) reduced the concentration of As in 9 L groundwater spiked with 200 μg/L As to <10 μg/L. In brief, covellite has good attributes of an adsorbent and is a candidate material for As remediation technologies.

Deposition of Arsenic from Nitric Acid Leaching Solutions of Gold–Arsenic Sulphide Concentrates

At present, the processing of refractory gold–arsenic sulphide concentrates is becoming more relevant due to the depletion of rich crude ore reserves. In the process of the nitric acid leaching of arsenic sulphide minerals, solutions are formed containing 20–30 g/L of arsenic (III). Since market demand for arsenic compounds is limited, such solutions are traditionally converted into poorly soluble compounds. This paper describes the investigation of precipitating arsenic sulphide from nitric acid leaching solutions of refractory sulphide raw materials of nonferrous metals containing iron (III) ions using sodium hydrosulphide with a molar ratio of NaHS/As = 2.4–2.6, which is typical for pure model solutions without oxidants. The work studied the effect of temperature, the pH of the solution and the consumption of NaHS and seed crystal on this process. The highest degree of precipitation of arsenic (III) sulphide (95–99%) from nitric acid leaching solutions containing iron (III) ions without seed occurs with a pH from 1.8 to 2.0 and a NaHS/As molar ratio of 2.8. The introduction of seed crystal significantly improves the precipitation of arsenic (III) sulphide. An increase in seed crystal consumption from 0 to 34 g/L in solution promotes an increase in the degree of transition of arsenic to sediment from 36.2 to 98.1% at pH = 1. According to SEM/EDS and XRF sediment data, from the results of experiments on the effect of As2S3 seed crystal consumption, acidity and molar ratio of NaHS/As on the precipitation of arsenic (III) sulphide and the Fetotal/Fe2+ ratio in the final solution, it can be concluded that the addition of a seed accelerates the crystallisation of arsenic (III) sulphide by increasing the number of crystallisation centres; as a result, the deposition rate of As2S3 becomes higher. Since the oxidation rate of sulphide ions to elemental sulphur by iron (III) ions does not change significantly, the molar ratio of NaHS/As can be reduced to 2.25 to obtain a precipitate having a lower amount of elemental sulphur and a high arsenic content similar to that precipitated from pure model solutions.

Arsenic removal from industrial effluent: In-situ ferric sulfate production and arsenic partitioning in the residues

Ferric sulfate solution was producedin situby sulfating arsenic-bearing, hematite-rich calcines (56–62% Fe2O3) with sulfuric acid, both produced by roasting refractory gold ore. The solution was then used for arsenic precipitation in the treatment of effluents from the cyanidation plant. The conversion of hematite to ferric sulfate increased as the acid/calcine ratio increased and reached 60.7%, with 0.87 of the stoichiometric acid amounts. An iron sulfate solution (13.4 g.L−1 Fe and 2.32 g.L−1 As) was produced at the end of the calcine sulfation/dissolution. Arsenic removal varied between 99.4 and 99.8%. Arsenic concentration dropped from 1583.4 mg.L−1 to 5.31 mg.L−1 As, which is far less than the industrial circuit's typical concentration (15 mg.L−1). Hydrated calcium sulfates were the principal constituents in the arsenical residues (i.e., 42–50%). Its removal allowed the identification of ferric arsenate/arsenite coprecipitates, arsenical ferrihydrite, and hydrated calcium-iron hydroxy-arsenate and hydrated calcium using X-ray diffraction analyses and Raman spectroscopy. The sequential extraction protocol and microscope automatic system confirmed the arsenic carriers. These are ferric (aluminum) or calcium arsenate/arsenites, accounting for 71.2 and 72.8% total As, and minor arsenic adsorbed on iron oxyhydroxides. Arsenic was primarily found (63.3%) in the Fe,Al-AsOx coprecipitates in the industrial residue. A 17% As-richer sludge, as achieved here (4.18% As), would result in a lower sludge volume for disposal. Transportation and disposal costs would then drop. These benefits were confirmed along one year of industrial operation. The projected reduction in effluent treatment costs reaches 60%.

Arsenate removal by resin-supported ferric ions: Mechanism, modeling, and column study

Removal of 10 mg/dm3 of As(V) by resin-supported Fe(III) was investigated in batch and column studies. The best As(V) removal was achieved at pH 3, and a high sorption density of 0.40 mmol-As/mmol-Fe was obtained after 96 h in a batch study. This sorption density could not be explained only by As(V) surface complexation with ferrihydrite. X-ray absorption near edge structure (XANES) analysis at the As K-edge suggested that over 90% of the As(V) was removed by surface precipitation as poorly crystalline ferric arsenate and the remainder was removed by surface complexation with ferrihydrite. XANES analysis at Fe K-edge suggested that 14%–35% of Fe(III) in the resin was used in the ferrihydrite and ferric arsenate. Kinetic modeling of the precipitation of ferrihydrite and ferric arsenate combined with a surface complexation model for As(V) and ferrihydrite successfully reproduced the batch experiment results. The kinetic constant for precipitation of ferrihydrite and ferric arsenate obtained by fitting of the batch experiment results successfully reproduced the column experiment results. The ratio of surface precipitation of ferric arsenate and As(V) surface complexation with ferrihydrite obtained by the constructed model was the same as in the XANES results. In the column study, a slow flow was advantageous for As(V) removal because surface precipitation of ferric arsenate took a long time.

Effect of Surface Deposition Coating with Aluminum Hydroxide on the Stabilization of Iron–Arsenic Precipitates

Effect of Surface Deposition Coating with Aluminum Hydroxide on the Stabilization of Iron–Arsenic Precipitates

Development of Technology of Arsenic Removal from Acidic Waste Solutions in the Form of Arsenic Trisulfide

During the laboratory tests the conditions of arsenic removal from acidic waste solutions of metallurgical enterprise in the form of arsenic trisulfide were determined. The technology based on the reduction of pentavalent arsenic to trivalent state with sodium pyrosulfite solution and following arsenic trisulfide precipitation from acidic solution after treatment with sodium sulfide solution was proposed. The arsenic removal proceeds with mechanical stirring, dosing the calculated amounts of reagents and collecting emissions of hydrogen sulfide. With such treatment, about 95% of arsenic, which was in the initial solution, passes into the precipitate. An enlarged laboratory experiment was carried out and the precipitate with 42.6% of arsenic and 46.9% of sulfur was obtained. The precipitate yield was ∼25.7 kg (dry weight) out of 1 m3 of the initial arsenic containing solution.&#x0D; Keywords: arsenic, arsenic trisulfide, acidic waste solutions, sodium sulfide, sodium pyrosulfite