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The best solution to address environmental pollution caused by arsenic-containing hazardous waste is to prepare high-purity elemental arsenic from such waste. The key to this approach lies in the efficient separation of arsenic from various impurities. This paper presents a viable solution for producing high-purity elemental arsenic from arsenic-alkali slag, and the keylies in utilizing the selective precipitation of magnesium ammonium arsenate (MgNH 4 AsO 4) to achieve efficient separation of arsenic from alkali, antimony, and other impurities. Thermodynamic analysis and hydrometallurgical condition experiments indicate that in complex alkaline arsenic-containing solutions, over 90% of arsenic components can selectively precipitate in the form of MgNH 4 AsO 4. The content of arsenic in the resulting precipitate reaches approximately 30%, while the content of antimony is below 0.1%. This achieves efficient enrichment of arsenic and preliminary separation of impurities in complex arsenic-alkali slag. Thermodynamic analysis and pyrometallurgical condition experiments demonstrate that the precipitate of MgNH 4 AsO 4 can be reduced to elemental arsenic with an arsenic content reaching 99.85%, and an antimony content as low as 0.05%. This achieves a profound separation of arsenic from impurities. Based on the research presented in this paper, a production line was established that enables the deep resource utilization of arsenic-alkali slag. [Display omitted] • The deep resource utilization of AAS was realized. • The arsenic in the AAS was separated in the form of MgNH 4 AsO 4. • 3. The MgNH 4 AsO 4 precipitate was reduced to elemental arsenic. • An annual AAS disposal line of 20,000 tons has been built. [ABSTRACT FROM AUTHOR]

• Aging of FeS nanoparticles seriously affects arsenic removal but slight on copper. • Controllable FeS are the targeted sulfurizing agents in different acidity wastewater. • BP-GA model are developed to precisely predict copper and arsenic removal with R of 0.9923. • Temperature and FeS aging time are necessary to gain high separation accuracy. • The model provides an essential reference in selecting sulfurizing reagent types. Iron sulfide (FeS) is a promising material for separating copper and arsenic from strongly acidic wastewater due to its S2− slow-release effect. However, uncertainties arise because of the constant changes in wastewater composition, affecting the selection of operating parameters and FeS types. In this study, the aging method was first used to prepare various controllable FeS nanoparticles to weaken the arsenic removal ability without affecting the copper removal. Orthogonal experiments were conducted, and the results identified the Cu/As ratio, H 2 SO 4 concentration, and FeS dosage as the three main factors influencing the separation efficiency. The backpropagation artificial neural network (BP-ANN) model was established to determine the relationship between the influencing factors and the separation efficiency. The correlation coefficient (R) of overall model was 0.9923 after optimizing using genetic algorithm (GA). The BP-GA model was also solved using GA under specific constraints, predicting the best solution for the separation process in real-time. The predicted results show that the high temperature and long aging time of FeS were necessary to gain high separation efficiency, and the maximum separation factor can reached 1,400. This study provides a suitable sulfurizing material and a set of methods and models with robust flexibility that can successfully predict the separation efficiency of copper and arsenic from highly acidic environments. [Display omitted] [ABSTRACT FROM AUTHOR]

The alkaline leaching process of arsenic-containing solid waste discharged during nonferrous metal smelting affords typical high-salinity alkaline arsenic-containing wastewater (HSAW). In this study, for the first time, Me (Ca2+ and Mg2+)–AsO 4 3−–OH−–H 2 O and Me (Ca2+ and Mg2+)–AsO 4 3−–CO 3 2−–H 2 O systems are studied based on a thermodynamic equilibrium diagram and an arsenic removal experiment, proving that the removal of arsenic using single metal ions in the presence of CO 3 2− is infeasible because of carbonate coprecipitation. Based on this observation, a new method that uses magnesium ammonium complex salts (MACSs) for HSAW treatment is proposed. Based on the thermodynamic calculations of the Mg2+–AsO 4 3−–NH 4 +–CO 3 2−–H 2 O system and the arsenic removal experiment, carbonate and arsenate can be selectively separated by the formation of magnesium ammonium arsenate (NH 4 MgAsO 4 ·6H 2 O). In an arsenic solution containing 150-g/L Na 2 CO 3 , the arsenic removal rate and the arsenic grade of the precipitation product reach 90.16% and 27.13%, respectively, when the molar ratios of Mg2+/NH 4 +:As(V) are 1.8:1 and 2:1, respectively. The proposed method is successfully employed for treating a leaching solution of alkaline arsenic slag discharged during antimony smelting. The findings of this study will broaden the basic theory of HSAW treatment and lay a foundation for the resource treatment of arsenic-containing solid waste. [Display omitted] • The traditional arsenic removal methods were infeasible in Na 2 CO 3 solution. • A method for the selective separation of arsenic and alkali by MACSs was proposed. • Arsenic component was precipitated in the form of MgNH 4 AsO 4. • The theoretical systems of arsenic removal by MACSs were established. • Alkaline arsenic slag can be disposed cleanly and safely by the novel method. [ABSTRACT FROM AUTHOR]

Here we report a system using ultrathin SnO 2 nanosheets with high reactive exposed (110) surface modified gold electrode for sensitive detection of As(III) by Square wave anodic stripping voltammetry (SWASV) with a mild acid condition (pH 5.0). Ultrathin SnO 2 nanosheets have been synthesized via a hydrothermal process successfully with the thickness of about 0.52 nm (four atomic layers thick). This oxide is used as electrode modifier, and the modified electrode exhibits good performance in stripping determination of As(III). The LOD actually measured is 5 μg L −1 and below the guideline value given by the World Health Organization (WHO). As compared with SnO 2 bulks, ultrathin SnO 2 nanosheets are found to exhibit stronger adsorption capability and better detection performance toward As(III), it may be due to the atomic thickness and extremely huge percentage of (110) facet ultrathin nanosheets materials exposed. Finally, this system is successfully applied for the analysis of a real sample collected from Inner Mongolia, China. Most importantly, we pose a potential for the use of ultrathin materials to improve the electrochemical performance of bare gold electrode in mild acid condition. [ABSTRACT FROM AUTHOR]

Leaching arsenic from solid waste selectively and removing arsenic from alkaline leachate efficiently are two key points in alkali treatment of copper smelter dust, and the latter is challenging. In this study, composite salt precipitation of magnesium ammonium arsenate (NH 4 MgAsO 4 ·6H 2 O), similar to magnesium ammonium phosphate (NH 4 MgPO 4 ·6H 2 O), was proposed to solve the difficult problem of separation arsenic from alkali. Based on the thermodynamic analysis, the selective leaching of arsenic from copper smelting dust was carried out in the NaOH-Na 2 S system. In the alkali leaching system, more than 80% arsenic can be leached out from the dust with the diffusion-controlled type in the Avrami model, while the leaching rates of valuable metals are less than 0.5%. For the strong alkaline leachate containing arsenic obtained by alkali leaching, the selective removal of arsenic was achieved by adding magnesium salt and ammonium salt. With the change of the amount of magnesium salt and ammonium salt, the sedimentation performance and composition of the arsenic slag changed accordingly. At the mole ratio of NH 4 +: As = 8:1 and Mg2+: As = 1.5:1, 96.38% of arsenic was removed, and the content of arsenic in the arsenic slag composed of MgNH 4 AsO 4 ·6H 2 O reached 28.96%. On this basis, the circulating alkali leaching of copper smelter dust based on arsenic-alkali separation was successfully carried out. The whole scheme is not only economical and safe, but also achieves the reuse of wastewater without secondary pollution, which provides an alternative solution for the treatment of arsenic containing solid waste. [Display omitted] • The selective arsenic leaching was realized in the NaOH-Na 2 S system. • The selective leaching of arsenic was in accordance with the Avrami model. • The removal of arsenic from alkaline leachate was realized by MgNH 4 AsO 4 ·6H 2 O. • The recycling alkali leaching was realized based on arsenic-alkali separation. • The reuse of alkaline waste water was realized by the novel scheme. [ABSTRACT FROM AUTHOR]

The accumulation of hazardous arsenic-alkali slag poses a great threat to the environment and human health due to the high content of soluble sodium arsenate. In this paper, a novel process scheme is proposed for the comprehensive utilization and safe disposal of arsenic-alkali slag by the combination of beneficiation and metallurgy. The new technology is novel since every procedure of high arsenic content is run at room temperature, which guarantees good occupational health. The valuable alkali and antimony were recovered efficiently without any secondary pollution. The separation of arsenic and alkali is the most difficult and critical section of the process, where magnesium salt and ammonium salt were added to the arsenic alkali solution in certain manner to selectively precipitate arsenic in the form of MgNH 4 AsO 4 ·6H 2 O (magnesium ammonium arsenate) and Mg 3 (AsO 4) 2 ·8H 2 O (magnesium arsenate). By controlling the addition of ammonium salt and magnesium salt, arsenic slag with high arsenic content, good sedimentation performance, and high crystallinity was produced. The arsenic slag can be stored by rigid landfill for the future development. The whole process is relatively simple and safer than existing approaches, providing an alternative solution for the treatment of hazardous arsenic-alkali slag. [ABSTRACT FROM AUTHOR]

Pyrrhotite is a potential source of S2− for the sulfide precipitation of nonferrous metal ions in hydrometallurgy and waste water treatment. In this study, different pyrrhotite crystals were prepared using zero-valent iron and sulfur to determine the effects of the pyrrhotite's structure on the sulfide precipitation of copper ions. The results indicate that the sulfide precipitation of copper ions highly depends on the crystal structure and crystallinity of pyrrhotite. Monoclinic pyrrhotite was found to be the most effective for copper sulfide precipitation, which can be used for the selective precipitation of copper ions from arsenic wastewater. More than 96% copper ions were removed with little loss of arsenic, contributing to a copper product of 20.2% Cu and 0.7% As, which can serve as raw materials of copper metallurgy. X-ray diffraction analysis showed the presence of CuS and (Cu x Fe 1 − x)S, indicating that most copper ions precipitated as CuS and some copper ions entered the FeS lattice by a lattice substitution reaction. Therefore, monoclinic pyrrhotite may provide an alternative solution for the selective precipitation of copper from arsenic wastewater. Unlabelled Image • SP (synthetic pyrrhotite) is more effective than NP (natural pyrrhotite) for copper removal. • Sulfide precipitation of Cu2+ depends on the structure of pyrrhotite. • CuS and (CuxFe 1 − x)S are the products of copper removal by monoclinic pyrrhotite. • SP has high selectivity for the copper and arsenic separation. [ABSTRACT FROM AUTHOR]

Abstract Arsenic contamination has raised great concern around the world as the cause of many severe health issues, including internal and external cancers. Discharging arsenic waste into the environment before proper handling is strictly forbidden. In order to treat the arsenic-bearing wastes in a safe way, we used the oxidation alkali leaching to dissolve arsenic in the low-risk state arsenate (AsO 4 3−) firstly, followed by recycling of the alkali solution after arsenate removal. In this paper, we synthesized high-concentrated ferric oxyhydroxide gels (HFGs) with different supersaturation in a hydrothermal system to adsorb arsenate anions at high alkali without consuming the hydroxyls. The arsenate adsorption onto HFGs followed the pseudo second-order and intra-particle diffusion kinetics and fitted Langmuir isotherms model well. Through characterization of the synthesized HFGs particles by XRD, Raman spectra, SEM and TGA, it was confirmed that the surface hydroxyl sites on the ferric oxyhydroxide reacted with arsenates to form the bidentate surface complexation. In addition, the synthesized HFG at lower supersaturation had lower crystallinity and more surface hydroxyl sites, resulting in higher adsorption capacity for arsenate. Using HFG as the adsorbent, the arsenic (V) concentration in the copper slag alkali leaching solution can be reduced from 2084 mg/L to 71.8 mg/L, which can realize stabilization of the high-concentrated arsenate at high alkali and alkali solution recycling. Highlights • Oxidation alkali leaching of the copper slag to removal As(V) in a low risk way • HFGs synthesized at different supersaturation for As(V) adsorption at high alkali. • Following PSO and intra-particle diffusion kinetics and Langmuir isotherms model • Forming monolayer arsenate-ferric bidentate surface complexation on HFGs surface • Achieving high-concentrated arsenic stabilization and alkali resource recycling [ABSTRACT FROM AUTHOR]

An electrochemical method for direct determination of inorganic arsenic [As(III), As(V), and total inorganic arsenic] was developed using an electrochemically etched gold wire microelectrode (Au-ME) by square wave anodic stripping voltammetry. Bromide was adopted to facilitate the electrochemical etching of gold through its complexation with gold ions, and controllably etched gold wire microelectrode can be obtained by adjusting the linear sweep voltammetry recycling numbers. Although the diameter of Au-ME decreases from 25.67 to 15.41 μm, for the determination of As(III) in 0.5 M H 2 SO 4 , the sensitivity increases 1.5-fold to 6.8 μA cm −2 ppb −1 and the limit of detection (LOD) decreases 2.8-fold to 2.6 ppb; for determination of As(V) in 0.25 M HCl, the sensitivity increases 1.6-fold to 2.6 μA cm −2 ppb −1 and LOD decreases 2.5-fold to 3.9 ppb. The As(V) deposition mechanism is put forward: first, chemically reduce to As(III) associated with active chlorine, and then electrochemically reduce to As(0), which experience two reduction step. Given that the LODs for both As(III) and As(V) are lower than the arsenic guideline value of 10 ppb, Au-ME shows efficiency in determining trace arsenic when applied to real environmental samples. [ABSTRACT FROM AUTHOR]