Arsenopyrite weathering in sodium chloride solution: Arsenic geochemical evolution and environmental effects

In situ electrochemical techniques and surface analysis were used to investigate the weathering behavior of arsenopyrite in chlorine-containing brine. Cyclic voltammetry measurements showed that arsenopyrite weathering releases S°, As (III) and Fe (II) during the initial step, even contains different concentrations of H⁺ and Cl^-, and terminal transformation into SO₄^2-, As (V) and Fe (III), respectively. Cl^- ions promote the arsenopyrite weathering through diffusion control or adsorption control when Cl- ions are at low or high concentrations. When C_cl^- increased from 0.00 to 0.05 mol/L, As (III) release increases from 549.33 to 1135.86 g·m^-2·y^-1, and the promotion efficiency is 107 %; whereas from 0.20 to 0.40 mol/L, the promotion efficiency is only 15.1 %. H⁺ ions accelerate arsenopyrite weathering for O₂ + 4H⁺ + 4e^- → 2H₂O, and the relationship between corrosion current density (i_corr) and pH is i_corr = -26.54 pH + 199.75. Raman spectra confirm that corrosion produces S° and As (V) and EDX shows the passivation layers are mainly composed of elements Fe, As, S and O, while the adsorption layer are mainly composed of elements Fe, As, S and Cl. The experimental results are of great significance for arsenopyrite geological environment assess and removal of arsenic ions.