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

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.