Recovery of arsenic oxide, harmless gypsum residue and clean water by lime neutralization and precipitation*

The nonferrous metal smelting industry-an influential industry in China-produces a large quantity of arsenic -containing acidic wastewater (ACAW) that seriously hinders the development of the industry. In this study, low-cost and effective methods for treating acidic wastewater were systematically examined. Lime neutralization and compound salt precipitation were used to remove arsenic (As) from acidic wastewater. The residues pro-duced during neutralization and compound salt precipitation were treated harmlessly by H2SO4 leaching, and As2O3 was recovered from the sulfuric acid leach solution (ALS). The results showed that the appropriate pH for the neutralization process was 3. The arsenic concentration in the solution after compound salt precipitation was <0.5 mg/L at pH 8.5 and suitable molar ratios (Cu/As: 0.45 to 2.3, Fe/As: 1.20 to 6.0, and Zn/As: 1.20 to 6.0). After acid leaching of residues obtained during neutralization and compound salt precipitation, the content of CaSO4 in the leach residue reached the specified value (CaSO4 >= 75 wt%) of industrial byproduct gypsum (GB/T 21371-2019 of China), and the concentration of arsenic in the toxicity leaching experiment was <5 mg/L. The ALS was reduced by SO2 to recover arsenic trioxide, and the recovery of arsenic reached 96.5%. Compared to the NaOH neutralization reagent, the lime treatment process is cost-effective and produces non-hazardous solid waste.

Automated summary

The nonferrous metal smelting industry in China produces a large amount of arsenic-containing acidic wastewater, which hinders the industry's development. This study examined low-cost and effective methods for treating acidic wastewater. Lime neutralization and compound salt precipitation were used to remove arsenic from the wastewater, and the residues were treated harmlessly by H2SO4 leaching to recover As2O3. The results showed that the lime treatment process was cost-effective and produced non-hazardous solid waste.