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

Arsenopyrite (FeAsS), the most common arsenic-bearing mineral, is usually found associated with pyrite (FeS ₂ ) in gold mining tailings. This work examined the galvanic effect of FeS ₂ 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 FeS ₂ particles and in the presence of different contents of this sulfide. The results indicated that the permanent, physical contact between FeAsS and FeS ₂ particles causes an increase in the accumulated As release, mainly under O ₂ -saturated conditions. At 30% wt. FeS ₂ , the increases relatively to FeS ₂ -free conditions were 82% and 117% in O ₂ -depleted and O ₂ -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. FeS ₂ ) to (1.1-1.9)× 10 ^-3 µmol m ^-2 s ^-1 (5-30% wt. FeS ₂ ) under O ₂ -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.
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