Stability of continuously produced Fe(II)/Fe(III)/As(V) co-precipitates under periodic exposure to reducing agents

•Arsenate co-precipitation with Fe(II) removes 99.9% As during co-precipitation.•Co-precipitation with Fe(II)/As(V)=4 reveal formation of ferrous arsenate.•Ferrous arsenate remains stable until it is oxidized.•Oxidation of Fe(II)–As(V) co-precipitates causes a minor spike in arsenic release.•As is re-stabilized after oxidation via re-adsorption or ferric arsenate formation. Arsenic mobilized during ore processing necessitates its effective removal from process effluents and disposal in environmentally stable tailings. The most common method to accomplish this involves co-precipitation with excess ferric iron during lime neutralization. The precipitates produced are stable under oxic conditions. This may not be true, however, under sub-oxic or anoxic conditions. In this context, the potential stabilizing role of ferrous iron on arsenic removal/retention becomes important. As such, this work investigates the removal and redox stability of arsenic with ferrous, ferric and mixtures of both. The stability of produced solids is monitored in terms of arsenic release over time. It was found that ferrous was very effective for arsenic (V) removal with Fe(II)/As(V)=4, reducing its concentration down to