Removal and immobilization of arsenic from copper smelting wastewater using copper slag by in situ encapsulation with silica gel

Abstract Ferric arsenate is an important arsenic-containing compound in the mining-impacted environment and hydrometallurgical tailings, especially in the disposal of smelting wastewater in nonferrous smelting industries. It acts as an intermediate for arsenic removal and immobilization in the disposal of arsenic-containing wastewater. However, amorphous ferric arsenate suffers from poor stability with a high arsenic leachability in the aqueous environment. In this study, we develop a new strategy to remove and immobilize arsenic from copper smelting wastewater using copper slag through an in situ encapsulation of ferric arsenate with silica gel. The strategy provides an inherent arsenic disposal solution for copper smelting processes, allowing the removal of arsenic in the form of environmentally friendly precipitates. The results show copper slag mainly composed of Fe2SiO4 and Fe3O4 can be dissolved in copper smelting wastewater containing high sulfuric acid and arsenic, providing abundant Fe3+ ions and silicates for the following arsenic precipitation. In the room-temperature solid-liquid reaction between copper slag and wastewater, the Fe-As co-precipitation and the in situ encapsulation results in an environmentally stable and core-shell structured precipitate consisting of an amorphous ferric arsenate core and a silica gel shell. Copper slag achieves an arsenic removal efficiency of 98.85% and an arsenic removal capacity of 66.86 mg/g in the disposal of smelting wastewater with an initial arsenic concentration of 8458 mg/L. The findings and proposed strategy demonstrates the potential for the efficient and affordable disposal of arsenic-containing wastewater.