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Abstract In this study, the removal effect of arsenic(V) was compared with different lead-containing substances, and the process of arsenic(V) removal with lead oxide was optimized. The results showed that As(V) removal efficiencies with lead powder, lead oxide, lead hydroxide and lead nitrate were 26.5%, > 99.9%, 98.5% and 96.3% at lead/arsenic(Pb/As) molar ratio of 2.12, respectively. Arsenic(V) removal with lead and its compounds was mainly based on the formation of mimetite. The removal of arsenic with lead oxide did not introduce impurity anions, and the crystallization performance and stability of the precipitate were relatively better than those of the precipitates obtained with other lead-containing substances. The crystallization performance of the precipitate was obviously improved when lead oxide was added twice. Using pH-conditioning in the process of arsenic removal, the residual lead in the solution could be removed via the co-precipitation of the hydrolysis of Pb2+ with mimetite. The highest As(V) leaching concentration of As—Pb precipitates was 0.2 mg/L at the pH of 1.9–12.3 with the leaching time of 1–48 h, and the stability of As—Pb precipitates could be improved by washing with dilute nitric acid. Lead oxide could be used as an effective reagent of arsenic removal in aqueous chloride solution. Highlights • Removal effect of arsenic(V) was compared with different lead-containing substances. • Arsenic(V) removal with lead oxide did not introduce impurity anions. • Stability of precipitates was improved by changing the addition ways of lead oxide. • The residual lead was removed by pH-conditioning in the process of arsenic removal. [ABSTRACT FROM AUTHOR]

• Efficient separation and recovery of arsenic and alkali were achieved. • Low consumption of sulfuric acid in the process of deep alkali removal. • The products recovered from arsenic-alkali solution were Na 2 CO 3 and As 2 O 3. • No arsenic-alkali mixed salts were produced in the separation process of arsenic and alkali. For the comprehensive utilization of antimony smelting arsenic-alkali residue, there are some problems such as the incomplete separation and low recoveries of arsenic and alkali, and the formation of arsenic-alkali mixed salts with secondary pollution. In order to solve these problems, the leaching solution of arsenic-alkali residue (arsenic-alkali solution) was used as a raw material in this study, and a novel process of twice alkali recovery with CO 2 , deep alkali removal with H 2 SO 4 , As(V) reduction with SO 2 and evaporation concentration to recover arsenic was proposed to dispose of the arsenic-alkali solution. The total recovery of alkali was 87.8% by twice alkali recovery from the arsenic-alkali solution. After washing and thermal decomposition of crude NaHCO 3 , the obtained Na 2 CO 3 product can be used as the reagent of arsenic removal in the refining process of crude antimony. In the process of deep alkali removal, compared with the direct treatment, the consumption of H 2 SO 4 after twice alkali recovery was markedly reduced from the arsenic-alkali solution, and also no mirabilite was precipitated. The total recovery of arsenic was 80.6% in the process of arsenic recovery, and the purity of As 2 O 3 in arsenic trioxide product reached 95.2% after washing, which meets the third grade standard of arsenic trioxide (GB 26721–2011). This process realizes the efficient separation and recovery of arsenic and alkali from the arsenic-alkali solution, and also no arsenic-alkali mixed salts are produced. [ABSTRACT FROM AUTHOR]

Arsenic-alkali residue is a hazardous waste produced by the refining process of crude antimony in antimony smelting, and contains highly toxic sodium arsenate and a large number of residual alkali. In this study, aiming at the problems of the low recoveries and incomplete separation of arsenic and alkali, the secondary pollution of arsenic-alkali mixed salts and the insufficient utilization of valuable resources in the treatment process of arsenic-alkali residue, a new process of antimony enrichment with water leaching, twice alkali recovery with CO 2 , selenium recovery with acidification and arsenic recovery with SO 2 reduction and evaporation concentration was proposed to dispose arsenic-alkali residue. The results showed that the leaching efficiencies of Sb, As, Se and alkali in arsenic-alkali residue were 1.8, 98.4, 97.9 and 100% by hot water leaching, respectively. Alkali was recovered with CO 2 from arsenic-alkali solution and the direct recovery was 87.8%. In addition, the purity of Na 2 CO 3 product was higher than 90% and As content in product was controlled below 0.2%. Deep alkali removal and efficient selenium recovery were achieved by acidification from the solution after alkali recovery, the direct recovery of Se was 80.6%, and the purity of crude selenium was 81.7%. Arsenic was recovered from the solution after selenium removal and the direct recovery was 79.4%, and the quality of As 2 O 3 product reached the third grade standard of arsenic trioxide (GB 26721-2011). This process realizes the efficient recovery of alkali, selenium and arsenic in arsenic-alkali residue, and also does not produce arsenic-alkali mixed salts and wastewater. • A new process was proposed to dispose antimony smelting arsenic-alkali residue. • The efficient recovery of alkali, selenium and arsenic was achieved. • Se was recovered in the form of elemental selenium without adding reducing agent. • The recycling process is clean and environmentally friendly. [ABSTRACT FROM AUTHOR]

• A combined process was proposed to purify crude As 2 O 3 and prepare high-purity As 2 O 3. • Above 95% As was extracted from crude As 2 O 3 by acidic oxidation leaching. • As(V) reduction process was controlled by both diffusion and chemical reaction. • The purification process is efficient and environmentally friendly. In this study, a combined process of acidic oxidation leaching and SO 2 reduction was proposed to purify crude As 2 O 3 recovered from antimony smelting arsenic-alkali residue. The effects of various process factors on crude As 2 O 3 leaching were investigated based on the thermodynamic analysis. The results showed that the leaching efficiency of arsenic was 95.5% when crude As 2 O 3 was leached with the mixed solution of H 2 SO 4 and H 2 O 2 under the conditions: the H 2 O 2 /As(III) molar ratio (n (H 2 O 2): n (As(III))) of 0.93, leaching temperature of 75 ℃, leaching time of 90 min and liquid-solid ratio of 4:1. The kinetic study of As(V) reduction with SO 2 gas showed that the reduction process conformed to the first-order gas/liquid reaction kinetics, and was controlled by both diffusion and chemical reaction with an apparent activation energy of 16.69 kJ mol−1. Arsenic could be directly recovered in the form of As 2 O 3 from leaching solution by SO 2 reduction, and the obtained product reached the standard of As 2 O 3 -1 (GB 26721-2011) after further purification. The direct recovery of arsenic was 85.8% after twice purifications for crude As 2 O 3. In addition, no arsenic-containing wastes were produced in the purification process. Overall, this process is efficient and clean for the purification of crude As 2 O 3. [ABSTRACT FROM AUTHOR]