CONTINUOUS CO-PRECIPITATION BEHAVIOUR AND STABILITY OF ARSENIC(Ⅴ) FROM Fe(Ⅱ,Ⅲ)-Al(Ⅲ)-Ni(Ⅱ) SULPHATE EFFLUENT SOLUTIONS

摘要

Several non-ferrous metal ores and concentrates contam significant amounts of arsenic that upon mobilization during hydrometallurgical processing necessitates its effective removal and disposal in environmentally stable tailings. The most common method to accomplish this operation involves lime neutralization in the presence of excess iron. It is known that for its effective co-precipitation, arsenic must be in its pentavalent state and iron as ferric at a molar ratio Fe(Ⅲ)/As(Ⅴ)＞3. Upon selection of the right pH profile the precipitates produced in this way are stable under oxic conditions. This may be not true however under sub-oxic or anoxic conditions that might develop in tailings ponds. In this context the potential stabilizing role of other co-ions becomes important. As such, this paper investigates the removal and redox stability of arsenic with ferric and various co-ions, Fe(Ⅱ), Al(Ⅲ), Ni(Ⅱ), in a 2-stage continuous co-precipitation process.