Arsenic Precipitates Research Articles

Controllable H2S supply via membrane contactors for safe and efficient arsenic precipitation from acidic wastewater

Sulfide precipitation is a popular technique for the treatment and resource recovery of arsenic-containing dirty acid wastewater. However, this approach frequently suffers from toxic hydrogen sulfide (H2S) escape and agent wastage issues. Herein, a safe and efficient technique is proposed based on a polytetrafluoroethylene membrane contactor wherein the mass transfer resistance of the gas, membrane, and liquid phases can be easily and independently regulated to control the H2S supply. Additionally, H2S is transferred in bubble-free form, fundamentally avoiding the issue of gas escape, and uniform membrane distribution contributes to evenly distributed H2S delivery. The results demonstrated that 99.3 % arsenic precipitation could be achieved and the H2S emission ratio was limited to < 0.12 %, which was significantly better than traditional methods. Thus, highly efficient separation and resource recovery of heavy metals in wastewater can be achieved using this unique and controllable low-dose H2S supply method. The separation factor between copper and arsenic was as high as 7490.9. This study provides a safe, reliable, and promising new approach for the treatment of arsenic-containing acidic wastewater.

Mechanisms of calcium-mediated As(V) immobilization by undissolved and dissolved biochar in saline-alkali environments

The environmental impact of arsenic (As) pollution has been a focal point within environmental science. In arsenic-polluted saline-alkali environment, the addition of exogenous biochar can affect the morphological transformation of As both through direct and indirect mechanisms, with calcium ions (Ca(II)) playing a crucial role. This study investigates the immobilization mechanisms of undissolved biochar (UOB) and dissolved biochar (DOB) on As(V) in the absence and presence of Ca(II) under alkaline conditions and aerobic atmosphere. While UOB and DOB alone are insufficient for As(V) immobilization, their combined action in the presence of Ca(II) achieves remarkable immobilization rates of 91.9% and 98.1%, respectively. Precipitation of calcium arsenate is identified as the primary immobilization pathway in both the UOB-Ca(II)-As(V) and DOB-Ca(II)-As(V) systems. Furthermore, Ca(II) acts as a mediator for As(V) immobilization through the formation of ternary UOB/DOB-Ca-As complexes, which are corroborated by Density Functional Theory (DFT) analysis from a microscopic perspective. Notably, the synergistic immobilization of As by DOB and newly generated CaCO3 in DOB-Ca(II)-As(V) system is highlighted. Additionally, the increase in Ca(II) concentration (0–100 mM) and solution pH (9.0–12.0) both significantly enhance the immobilization of As(V). An increase in the dosage of UOB (0.4–4 g/L) reduces the immobilization of As(V), while effect of the DOB concentration is insignificant. This study provides new insights into how the release of two biochar fractions into a typical Ca(II)-rich saline-alkali environment may alter the fate and transport of As species.

Study on the influence of active oxygen on the natural oxidation of arsenopyrite under different temperature conditions

Arsenic (As), a toxic element, contaminates farmlands, rivers, and groundwater, posing severe environmental and health risks. Notably, As-containing materials in tailings are affected by temperature variations during long-term storage, and this considerably impact the oxidation and migration of elements in arsenopyrite.This study focused on arsenopyrite and investigated the process of its oxidative dissolution and release of arsenic under different temperature conditions by using in-situ XRD, in-situ XPS and electron paramagnetic resonance spectroscopy(EPR), The role of oxygen free radicals in the oxidation of arsenopyrite was elucidated. It has been established that under high-temperature conditions As, iron (Fe), and sulfur (S) are primarily present As(V)/As(IV), Fe(III), and SO42−, respectively. The O2⋅− generated during the oxidation of As(III) by O2, OH⋅ produced by the Fe(II)/FeOH2+ reaction, and H2O2 formed via their interaction play a crucial role in the photochemical oxidation of arsenopyrite. These findings provide a theoretical basis for the formation of ferric arsenate precipitation, contributing in the adsorption and immobilisation of oxidatively released arsenic.

Assessment of water supply to the east European arctic agglomeration from groundwater, taking into account their quality and health risks

The purpose of the study is to assess the possibilities of using groundwater for water supply in the East European Arctic agglomeration based on an assessment of their quality and health risks. For this purpose, high-precision determinations of the complete macro- and microcomponent composition were carried out in sixty-six water samples taken from wells up to 180 m deep. It was found that in some samples the concentrations of Na+, Fe, B, Ba, Mn and U exceeded WHO standards. The least mineralized young waters are characterized by the processes of dissolution of carbonates with the transition of Ca, Mg, Ba, Sr into water, and the processes of leaching of Fe and Mn by acidic swamp waters from near-surface sediments. Waters of high mineralization, enriched in Na+, Cl-, B, Mo, Cd, Pb, were formed as a result of the dissolution of aluminosilicate rocks over thousands of years and mixing with relics of ancient and modern marine transgressions. An assessment of the average Water Quality Index value of the studied aquifer showed that, in general, the water is of excellent quality. Non-carcinogenic risks were determined primarily by uranium concentrations. The average danger index values for this element for children were 1.22. In adults it was slightly lower and amounted to 0.83. Carcinogenic risks are associated primarily with arsenic concentrations. The average total carcinogenic risk associated with this element was 3.8.10−5, which is acceptable, but samples from two wells showed total carcinogenic risk values above 10−4, which is in the high-risk area. For drinking purposes, it is preferable to use low-mineralized water with a minimum content of toxic elements. If necessary, preliminary aeration of the water is possible, during which precipitation of iron, arsenic and uranium occurs. Due to the typical nature of the problem under consideration for the Arctic regions, the results obtained can be used at other sites in the Subpolar zone.

PRECIPITATION OF ARSENIC FROM THERMAL WATER

The presented scientific research reveals the results of experiments on the precipitation of arsenic in the form of sulfide (As2S3) from the Daridag thermal water using sodium sulfide as a reagent. The main factors impacting the precipitation of the As2S3 compound were determined: the amount of precipitant (Na2S), the ratio of solid and liquid phases (S:L), pH of the initial solution, precipitation time and temperature, also optimal parameters were obtained. According to the results obtained, the yield during precipitation of arsenic tri-sulfide from from thermal water under certain temperature conditions (t=30-450С, pH=1-2; S:L - 1:1000; = 30-50 min.) were 99.6 %. The properties of the samples were studied by physicochemical research methods (X-Ray, SEM/EDS). X-ray phase analysis showed that the sediment sample obtained under these conditions is X-ray amorphous. The composition and morphology of the obtained sample was confirmed by scanning electron microscopy and spectroscopy (SEM/EDS)

Study on Hydrothermal Arsenic Fixation in H3AsO4-FeSO4-Na2SO4-H2O System

In this study, hydrothermal metallurgy technology was used to convert arsenic in the solution into a stable, dense, and granular arsenic-fixing mineral, scorodite (FeAsO4·2H2O), that is conducive to storage. The effect of Na+ on the precipitation rate of arsenic and iron, the phase composition, and the transformation of arsenic residue during the mineralization and arsenic precipitation of hydrothermal scorodite in the H3AsO4-FeSO4-Na2SO4-H2O system were studied. The results show that Fe3+ co-precipitates with As5+ to form scorodite (FeAsO4·2H2O). In the later stage of the reaction, Fe3+ and Na+ combine to precipitate in the form of sodium jarosite [NaFe3(SO4)2(OH)6]. Under the conditions of an initial Na+ concentration of 10 g/L, an arsenic concentration of 10 g/L, a molar ratio of iron to arsenic of 1.5, a pH of 1, a reaction temperature of 160 °C, a stirring speed of 500 r/min, a reaction time of 3 h, and an oxygen partial pressure of 0.6 MPa, the precipitation rates of arsenic and iron were 98.2% and 93.2%, respectively. The phase composition of the arsenic residue is mainly composed of large-grained polyhedral crystal scorodite, and a small amount of irregular, small-grained crystal sodium jarosite is dispersed in it. By controlling the initial molar ratio of iron to arsenic, the concentration of Na+, and prolonging the reaction time, the formation of the sodium jarosite phase can be inhibited, and the transformation of the sodium jarosite phase into the scorodite phase can be promoted, so as to realize the efficient precipitation of arsenic, reduce the amount of arsenic residue, ensure the stability of arsenic residue, and avoid potential environmental pollution risks.

Effects of Composition and Cooling Rate on Mechanical Properties of Pb-Sb-Sn-As Grid Alloys

The effects of chemical composition and cooling rate on the mechanical properties of Pb–Sb–Sn–As grid alloys for lead-acid batteries were investigated. Mechanical properties were characterized in terms of ultimate tensile strength and elongation at room temperature. Composition and cooling rate of the studied alloys should ensure the increase in the amount of Sn soluble in α-Pb and the decrease in the amount of brittle arsenic precipitates or eutectic β-Sb phase in the structure.

Deep separation of arsenic and alkali from alkaline arsenic containing solution using hydrothermal lime precipitation method

A new strategy of lime precipitation of arsenic (As) under hydrothermal conditions was proposed for the treatment of alkaline arsenic-containing wastewater (AAW). On the basis of theoretical analysis, a study was conducted on the reaction law and mechanism of lime precipitation of arsenic in hydrothermal systems, as well as the environmental stability of precipitation products. Results of theoretical calculations showed that increasing the reaction temperature was beneficial the formation of insoluble Ca5(AsO4)3OH, which promoted the removal of arsenic. It is shown that the arsenic concentration could be reduced from 35.38 mg/L to 9.16 mg/L with increasing the reaction temperature from 90 °C to 210 °C. The experimental results further confirmed the above conclusion. When the reaction temperature was increased from 90 °C to 210 °C, the arsenic concentration in the final liquid decreased from 706.21 mg/L to 15.21 mg/L. The leaching toxicity evaluation results of the products showed that the stability of the arsenic precipitates was improved significantly with the hydrothermal conditions. The arsenic leaching concentration for the products obtained at 170 °C was only 2.1 mg/L, which was lower than the U.S. Environmental Protection Agency (USEPA) limit of 5 mg/L for solid waste containing hazardous arsenic. It is found that the improved stability of the arsenic precipitates could be attributed to the increased crystallinity and crystal size of the product obtained under hydrothermal conditions.

Simultaneous adsorption of chromate and arsenate onto ferrihydrite/alginate composite beads: Competition and mechanism

Ferrihydrite is an effective adsorbent of chromate and arsenate. In order to gain insight into the application of ferrihydrite in water treatment, macroporous alginate/ferrihydrite beads, synthesized using two different methods (internal and encapsulation processes), were used in this work. The properties of the ferrihydrite were assessed using various techniques, including X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) theory, and zetametry. The results showed that the specific surface area of the ferrihydrite was 242 m2/g, and the PZC was pH8. The kinetic and isotherm adsorption properties of the ferrihydrite were evaluated in this study. The results indicate that the pseudo second-order and Freundlich models accurately describe the kinetic and isotherm adsorption properties of chromates and arsenates. For chromate removal, ferrihydrite exhibited a relatively high adsorption capacity (40.7 mgCr/g) compared to other adsorbents. However, the arsenate adsorption capacity of MFHB-SI (140.8 mgAs/g) was shown to be the most optimal. The internal synthesis process was suitable for arsenate retention due to the resulting arsenate precipitation. The competitive adsorption analyses indicated that the presence of chromate does not limit the adsorption of arsenate. However, the presence of arsenate almost completely inhibits the adsorption of chromate when the arsenate concentration is above 50 mg/L, due to the precipitation reaction of arsenate.

A novel method for rapid and highly selective removal of arsenic from copper electrolyte using zirconium salts

Copper electrolytes generally contain high concentrations of arsenic (As), which is very harmful in copper electrolytic production. In this paper, a zirconium salt, which selectively precipitated arsenic, was added to the electrolyte to realize rapid and efficient arsenic removal. The effects of zirconium salt addition, the reaction temperature, reaction time and different electrolytes on arsenic removal were systematically investigated, the concentration equilibrium curves for As and Zr were established at different temperatures, the effects of residual zirconium ions on copper electrolysis were evaluated, and a theoretical study of the arsenic removal process was carried out. The results showed that with the optimal conditions for arsenic precipitation, 85.41 % of the As was removed from the industrial electrolyte, and the As concentration in the electrolyte was decreased to 1.41 g/L. Regeneration of the precipitates was achieved in NaOH solutions, and the regenerated precipitates exhibited efficient As removal. The As–Zr reactions followed a third-order kinetics model, and the apparent activation energy was 36.42 kJ/mol. Furthermore, the As–Zr reaction pathway, transition state structure and microscopic valence bonding changes were investigated with density functional theory (DFT). This research provides a promising method for processing copper electrolyte with high contents of As.

TECHNOLOGIES FOR WASTEWATER TREATMENT FROM ARSENIC

The current recycling water supply of metallurgical enterprises does not completely eliminate the discharge of wastewater into environmental water bodies, where the maximum permissible concentration (MPC) of arsenic is 0.05 mg/dm3. Arsenic accumulates in large quantities in washing solutions for cleaning exhaust gases sent to produce sulfuric acid. In this case, a closed gas washing system is used, aimed at concentrating the washing water with arsenic to 10 g/dm3 and sulfuric acid to 40 g/dm3 in order to reduce the volume of wastewater discharge. Another source of arsenic contamination of the hydrosphere is the waters of tailings from enrichment plants, due to the possible oxidation of arsenopyrite and the formation of a soluble form of arsenic compounds.&#x0D; A number of methods for arsenic precipitation have been developed: pyrolusite, lime in the form of calcium arsenate; ions of ferric iron and other metals; adsorption by iron (III) hydroxide, aluminum hydroxide, carbon, etc.; sludge flotation; metal sulfides, sorption and extraction. The main criterion for the operation of purifying a solution from arsenic is the possibility of recycling the resulting sediment or the formation of its compounds with minimal solubility in aqueous solutions, allowing its burial in burial grounds.

A simple and rapid copper-assisted microprecipitation method for the on-site separation of inorganic arsenic species in water samples followed by hydride generation atomic fluorescence spectrometry determination

A simple and rapid microprecipitation procedure was developed using copper (Cu2+) as precipitating agent for the separation–preconcentration of inorganic arsenic species (As(III) and As(V)) in waters prior to their determination by hydride generation atomic fluorescence spectrometry (HG-AFS). This procedure is based on selective precipitation of anionic species of As(V) with Cu2+, leaving neutral As(III) in the filtrate. The complexation of As(V) with Cu(II) entails the precipitation as copper arsenate, Cu3(AsO4)2 due to its low solubility product. The copper arsenate precipitate was characterized by XRD and EDS measurements. Optimum conditions for efficient microprecipitation process are; pH: 5 to 6, Cu/As mass ratio: 100, equilibration time: 2–3 min and eluent volume: 2 mL of 0.03 mol L−1 HCl. A fast process time of 2 min is enough for the on-site separation of As(III) and As(V) with the detection limits (LOD) 0.012 and 0.034 μg L−1 respectively. The recoveries were found to be in the range of 98–102%. This simple and fast method was successfully utilized for the on-site separation of As(III) and As(V) in wide variety of water samples collected in and around Kiradalli Tanda village, Karnataka state, India, where severe arsenic-contamination exists in various water bodies.

A green process for arsenic removal and tungsten recovery from tungsten residue waste: Focused on the separation and recovery of arsenic and tungsten via solvent extraction followed by H2S precipitation

Tungsten residue waste (TRW) has been recognized as a hazardous solid waste by Chinese government due to its high As content and leaching toxicity. This paper presents a green full process for efficient arsenic removal and tungsten recovery from hazardous TRW, focusing on the separation and recovery of arsenic and tungsten from leach solution of TRW via solvent extraction with N235 followed by H2S precipitation. The results showed that the W recovery was nearly 100% and As, Si, S removal was 96.68%, 86.93% and 99.73%, respectively, under optimized conditions. Most of the As(Ⅲ) is extracted in the organic phase as H3AsO3 through hydrogen bonding. During the oxidative scrrubbing process, most of As(Ⅲ) was oxidized to As(Ⅴ) and scrubbed. As(Ⅴ) in the scrubbed organic phase mainly existed in the form of [As2W18O62]6-. The arsenic (∼26 g/L) in the raffinate was then completely removed by sulfide precipitation with 99.6% of As precipitation. The arsenic precipitation slag was a mixture of As2S3 and S with a mole ratio close to 1:1. The arsenic precipitation mother liquor was first cooled and crystallized, followed by causticization with lime to a NaOH concentration of 70 g/L, which can be used for the leaching of hazardous TRW. A green process of TRW harmless treatment and W recovery was proposed, and the flow of As and W in the process was analyzed. The closed-loop strategy shows great promise for the harmless treatment and tungsten recovery of TRW on an industrial scale to promote circular economy and environmental protection.

Effect of dissolved metal species on arsenic precipitation and stability during the pressure oxidation of arsenopyrite

This work investigated the influence of dissolved Al3+, Ca2+, Cu2+ and Mg2+ cations on the behaviour of As during the acid pressure oxidation of arsenopyrite at 210˚C. Basic ferric arsenate sulfate was the major As-bearing product in the baseline after 1 h, and a similar result and degree of As precipitation was observed at up to 5,000 ppm of Al3+ and up to 500 ppm of Ca2+, Cu2+, and Mg2+. At 5,000 ppm of Cu2+, basic copper ferric arsenate was formed as a co-product along with improved As precipitation, while 5,000 ppm of Mg2+ resulted in scorodite as a minor product, potentially formed during cooling due to As co-precipitation following the dissolution and oxidation of Fe(II). All samples exhibited similar As stabilities, with As leachability near 10 ppm compared to the recommended limit of 5 ppm. The experimental and thermodynamic modelling results suggest that the dissolved cations at the studied concentrations have a beneficial impact on the removal of As under the investigated conditions. Subsequently, density functional theory calculations on doped scorodite indicated that ionic substitution of Fe with Al, Ca or Mg enhanced the stability of the crystal structure, while the opposite was observed with Cu due to increased reactivity of the Cu in the crystal.

Effective treatment of high-arsenic smelting wastewater: Immobilization arsenic and synthesis well-crystallized scorodite

As-containing acidic wastewater from the nonferrous heavy smelting industry is a hazardous As pollution source due to its complex composition, high acidity, and strong toxicity. In this study, an environmentally friendly strategy was proposed to simultaneously remove and immobilize As from acidic wastewater through the synthesis of highly stable scorodite using natural magnetite ore as Fe resource. Firstly, the magnetite ore was dissolved in wastewater to provide a certain amount of starting Fe source for the subsequent arsenic precipitation while creating a suitable pH environment for the synthesis of scorodite. Subsequently, the released Fe ions reacted with As ions in wastewater with undissolved magnetite ore as the nuclear site to form amorphous ferric arsenate, which was then transformed into a well-crystallized scorodite precipitate, thus achieving the As removal and immobilization. Under the optimal reaction conditions, including a Fe/As molar ratio of 2.5, a pre-dissolution time of 5 h, an initial pH of 2.0, a reaction time of 24 h, and a reaction temperature of 90 °C, the residual As concentration in the wastewater rapidly reduced from initial 6259.00 mg/L to 3.76 mg/L, corresponding to an arsenic removal efficiency of 99.94%, and the leaching As concentration in scorodite was 0.42 mg/L. This study provides an efficient and environmentally friendly method for the disposal of high As-containing wastewater from nonferrous smelting.

Immobilizing arsenic-enriched wastewater from utilization of crude antimony oxides as scorodite using a novel multivalent iron source

Arsenic–enriched wastewater (A–EW) is a hypertoxic sewage from the utilization of crude antimony oxides in lead anode slime metallurgy. In traditional methods, the H+ accumulation inhibits the arsenic immobilization during scorodite synthesis. In this study, a novel multivalent iron source comprised of Fe(OH)3 and FeSO4·7H2O was proposed to resolve the adverse effects of pH fluctuation during immobilizing A–EW as scorodite. Various approaches, such as scanning electron microscopy and X–ray photoelectron spectroscopy, were applied to characterize the synthesized scorodite. This work was divided into two parts. In thermodynamics, HnAsO4(3−n)- (n = 1, 2, 3) and Fe(OH)n(3−n)+ (n = 0, 1, 2, 3) can feasibly coprecipitate as scorodite according to their △rGm,Tθ ranged from −111.10 kJ mol−1 to −33.53 kJ mol−1. In experimental research, A–EW was immobilized as scorodite by optimizing conditions as initial pH = 2.0, molar ratio of Fe to As = 1.2, molar ratio of Fe(II) to Fe(III) = 4:6, arsenic concentration = 40 g/L, and temperature = 95 °C. The arsenic precipitation ratio is 99.60%, and the micromorphology of synthesized scorodite presents a regular octahedron having size of 5–10 μm. The low leachability of As (0.41 mg/L) in toxicity characteristic leaching procedure (TCLP) confirmed that the prepared scorodite is nonhazardous. The solution pH is stable at 2.0 as the H+ depletion (0.5660 mol) by Fe(OH)3 dissolution and Fe2+ oxidization balanced with that (0.5657 mol) generated from As(V)–Fe(III) coprecipitation. In general, the A–EW was effectively immobilized by proposed multivalent iron source, and can be potentially applied to safely dispose other industrial effluents, such as high arsenic leachates and arsenic–bearing waste acid from nonferrous metallurgy.

Efficient removal of p-arsanilic acid and arsenite by Fe(II)/peracetic acid (Fe(II)/PAA) and PAA processes

The widespread occurrence of p-arsanilic acid (p-ASA) in natural environments poses big threats to the biosphere due to the generation of toxic inorganic arsenic (i.e., As(III) and As(V), especially As(III) with higher toxicity and mobility). Oxidation of p-ASA or As(III) to As(V) followed by precipitation of total arsenic using Fe-based advanced oxidation processes demonstrated to be a promising approach for the treatment of arsenic contamination. This study for the first time investigated the efficiency and inherent mechanism of p-ASA and As(III) oxidation by Fe(II)/peracetic acid (Fe(II)/PAA) and PAA processes. p-ASA was rapidly degraded by the Fe(II)/PAA process within 20 s at neutral to acidic pHs under different conditions, while it was insignificantly degraded by PAA oxidation alone. Lines of evidence suggested that hydroxyl radicals and organic radicals generated from the homolytic OO bond cleavage of PAA contributed to the degradation of p-ASA in the Fe(II)/PAA process. p-ASA was mainly oxidized to As (V), NH4+, and p-aminophenol by the Fe(II)/PAA process, wherein the aniline group and its para position were the most vulnerable sites. As(III) of concern was likely generated as an intermediate during p-ASA oxidation and it could be readily oxidized to As(V) by the Fe(II)/PAA process as well as PAA alone. The in-depth investigation demonstrated that PAA alone was effective in the oxidation of As(III) under varied conditions with a stoichiometric molar ratio of 1:1. Efficient removal (> 80%) of total arsenic during p-ASA oxidation by Fe(II)/PAA process or during As(III) oxidation by PAA process with additional Fe(III) in synthetic or real waters were observed, mainly due to the adsorptive interactions of amorphous ferric (oxy)hydroxide precipitates. This study systematically investigates the oxidation of p-ASA and As(III) by the Fe(II)/PAA and PAA processes, which is instructive for the future development of arsenic remediation technology.

Flue gas arsenic trioxide removal from sludge incineration by sulfate-reducing membrane biofilm reactor

Arsenic in flue gas from sludge incineration may damage to human health and ecological environment seriously. The sulfate-reducing membrane biofilm reactor (SRBR) was investigated for arsenic trioxide(As2O3) removal in flue gas from sludge incineration. Arsenic removal efficiency attained 94.4%. Desulfovibrio, UC_Clostridiales, and Pseudodesulfovibrio were the dominant genera. Desulfovibrio was the core arsenite-oxidizing-sulfate-reducing genus. Arsenite oxidase (ArxA) and sulfate-reducing enzymes (Sat, AprAB and DsrAB) responsible for bacterial As(III)-oxidation and sulfate reduction. Desulfovibrio could synthetically regulate the expression of functional proteins that involved in As oxidation, sulfate reduction, cell wall and membrane synthesis, antioxidant, DNA repair, glycolysis and amino acid synthesis under As stress, possessed resistant and removal ability to As. The biofilm in SRBR was characterized by FTIR, XPS, XRD, EEM, and SEM-EDS. XPS and XRD spectra indicate the formation of an arsenic species (As(V)) from arsenic oxidation. Humic acid complex arsenic (HA-As) and arsenopyrite-like phase (Fe-As-S) precipitation were formed in SRBR. Microbial arsenic oxidation was coupled sulfate reduction and biostabilization of arsenic from flue gas. Arsenic in flue gas was bio-stabilized in the form of Fe-As-S and HA-As via biocomplexation of humic acids in extracellular polymeric substances (EPS), biosorption and biodeposition. These results show that the sulfate-reducing membrane biofilm reactor is achievable and open new possibilities for applying the SRBR to removal of arsenic in flue gas from sludge incineration.

Arsenic triggered nano-sized uranyl arsenate precipitation on the surface of Kocuria rosea

Arsenic (As) and uranium (U) frequently occur together naturally and, in consequence, transform into cocontaminants at sites of uranium mining and processing, yet the simultaneous interaction process of arsenic and uranium has not been well documented. In the present contribution, the influence of arsenate on the removal and reduction of uranyl by the indigenous microorganism Kocuria rosea was characterized using batch experiments combined with species distribution calculation, SEM–EDS, FTIR, XRD and XPS. The results showed that the coexistence of arsenic plays an active role in Kocuria rosea growth and the removal of uranium under neutral and slightly acidic conditions. U-As complex species of UO2HAsO4 (aq) had a positive effect on uranium removal, while Kocuria rosea cells appeared to have a large specific surface area serving as attachment sites. Furthermore, a large number of nano-sized flaky precipitates, constituted by uranium and arsenic, attached to the surface of Kocuria rosea cells at pH 5 through P=O, COO−, and C=O groups in phospholipids, polysaccharides, and proteins. The biological reduction of U(VI) and As(V) took place in a successive way, and the formation of a chadwickite-like uranyl arsenate precipitate further inhibited U(VI) reduction. The results will help to design more effective bioremediation strategies for arsenic-uranium cocontamination.

Occurrence Behaviors of As/Sb/Bi in Copper Anode Slime and Their Separation by Compound Leaching Followed by Stepwise Precipitation.

Copper anode slime is the main raw material for the extraction of rare and precious metals. However, the recovery of rare and precious metals still faces great challenges due to the variety of impurities and the complex occurrence phase. In view of this, this research focuses on the occurrence mineral phases of arsenic, antimony, and bismuth in copper anode slime, and the process consisting of chloride leaching and selective precipitation of arsenic and bismuth is proposed. The results show that in copper anode slime, As mainly exists in the form of arsenate, while Sb and Bi exist in the form of oxides. The arsenate and oxides of Sb and Bi can be effectively leached by using the compound leaching process in the chloride system. The leaching efficiencies of As, Sb, Bi, and Cu can reach 92.72, 99.98, 89.13, and 90.31%, respectively, using a H2SO4 concentration of 4 mol/L and a NaCl concentration of 120 g/L with a liquid-solid ratio of 10:1 at 70 °C for 2 h. After compound leaching, more than 98% of Sb and Bi can be separated by stepwise selective precipitation in the form of Sb4O5Cl2 and BiOCl by controlling the H+ concentration at 0.8 g/L and 0.2 g/L, respectively. After separation of Sb and Bi, the As-containing solution can be further treated by mature arsenic solidification technology. The copper-containing solution for removing arsenic, antimony, and bismuth can be returned to the electrolysis process for copper recovery. The proposed process realizes the effectively and environmentally friendly separation of As, Sb, Bi, and Cu from copper anode slime.