Stability of arsenopyrite and As(III) in low-temperature acidic solutions

Abstract

Arsenopyrite is one of the most important primary arsenic mineral. It is easily oxidized under hypergene conditions to release Fe, As, S and other elements. Of the released elements, dissolved arsenic is an extremely toxic element. It is of particular importance to study arsenopyrite and the conversion of As species for environmental protection. This paper deals with the stability of arsenopyrite and As(III) in acidic Fe 2 (SO 4 ) 3 and FeCl 3 solutions with the concentrations within the range of 10 -2 —10 -5 mol·kg -1 . Experimental researches revealed the following points: (1) under the conditions of the experiment arsenopyrite is unstable and its oxidation extent tends to increase with increasing Fe 3+ concentration and reaction temperature and decreasing pH; (2) arsenic released during the oxidation of arsenopyrite is dominated by hydrous oxides of As(III); (3) in the FeCl 3 solution the oxidation rate of arsenopyrite and As(III) toward As(V) is faster than in the Fe 2 (SO 4 ) 3 ; and (4) the stability of As(III) tends to increase with decreasing oxidant concentration and reaction temperature, but to decrease with increasing Cl - concentration and illuminance.