Galvanic effect of pyrite on arsenic release from arsenopyrite dissolution in oxygen-depleted and oxygen-saturated circumneutral solutions

Abstract

Arsenopyrite (FeAsS), the most common arsenic-bearing mineral, is usually found associated with pyrite (FeS2) in gold mining tailings. This work examined the galvanic effect of FeS2 on As release from FeAsS oxidation in circumneutral media under oxygen-depleted and oxygen-saturated conditions. The oxidation experiments were conducted with a flow-through reactor in the absence of FeS2 particles and in the presence of different contents of this sulfide. The results indicated that the permanent, physical contact between FeAsS and FeS2 particles causes an increase in the accumulated As release, mainly under O2-saturated conditions. At 30% wt. FeS2, the increases relatively to FeS2-free conditions were 82% and 117% in O2-depleted and O2-saturated solutions, respectively. At steady-state, the As release rates increased from (4.9 ± 0.5)× 10−4 µmol m−2 s−1 (0% wt. FeS2) to (1.1–1.9)× 10−3 µmol m−2 s−1 (5–30% wt. FeS2) under O2-saturated conditions. Analysis of FeAsS samples after oxidation revealed oxidized particles partially or entirely covered by precipitates with different sizes, shapes and compositions (e.g., As−S−bearing ferrihydrite, elemental sulfur, and As−O phases). A fine (3–4 nm thick) amorphous layer of S−As−bearing ferric oxy-hydroxide was also identified on oxidized FeAsS, with Fe(III) and As(III) species.