Disposal of arsenic in copper discharge slags

Arsenic, which is a toxic pollutant, is present in copper minerals in concentrations to around 1 wt.%. During processing of such copper feed materials, the arsenic has to be transformed into an environmentally acceptable form. Laboratory experiments have been carried out to determine the feasibility of incorporating the arsenic in discharge slags for long-term disposal. Iron arsenate (FeAsO(4)) samples were prepared and tested under various conditions. Upon heating to about 900 degrees C, basically no arsenic was lost. However, at and above 1000 degrees C, iron arsenate decomposes rapidly and arsenic volatilizes. The incorporation of iron arsenate in liquid slags at around 1250 degrees C was difficult due to rapid arsenate decomposition and dust losses during the injection process. Although the leaching tests showed that the slags could meet environmental regulations, the fraction of arsenic leached was no less for the slag samples than for the initial iron arsenate itself.