Efficient removal of arsenic from copper smelting wastewater via a synergy of steel-making slag and KMnO4

Abstract

Copper smelting wastewater, one of the most significant sources of arsenic pollution from the copper extraction process of arsenic-associated minerals, seriously impedes the attainment of sustainable industrial development due its tremendous disposal cost and the potential risks it poses. Steel-making slag can effectively detoxify low arsenic-bearing wastewater, but its low removal rate, low adsorption capacity, and high arsenic concentration limit its large-scale application. In the study, we propose a cost-effective and feasible strategy for the disposal of high arsenic-bearing wastewater from copper smelting plant via a synergy of steel-making slag and permanganate (KMnO4). Steel-making slag dissolved in wastewater releases Fe, Ca, and Si ions while simultaneously increasing the pH value of the solution. Afterward, As(III) and Fe(II) are oxidized to As(V) and Fe(III) in situ through the permanganate, generating an amorphous FeAsO4 precipitate and As-adsorbing Fe(OH)3 flocs. The dissolution and oxidization reaction is driven by a mutually improved cycle of reduction-generated H+ and MnO2, ensuring the continuous precipitation and adsorption of As. In this study, the synergy between steel-making slag and KMnO4 successfully achieved an arsenic removal rate of 91.37% and an arsenic removal capacity of 32.37 mg/g with an initial arsenic concentration of 1834 mg/L and a sulfuric acid concentration of 2800 mg/L. In combination with the adjustment of the pH value, subsequently, residual Fe, Ca, and Si ions were further hydrolyzed in the form of new Fe(OH)3 flocs and a Ca2SiO4 gel, promoting the deep purification of the wastewater. The final residual arsenic concentration achieved was 1.54 mg/L at a pH value of 10. Based on this study case, a process by which cooper smelting wastewater can be successfully treated via the synergy of steel-making slag and KMnO4 is proposed, which is potentially feasible for industrial application.