Abstract
The main treatment method for the removal of arsenic from process and effluent streams, and also from drinking water, has employed chemical coprecipitation with Fe(III) and Al(III) for many decades. It is considered that As(V) is the oxidation state that is most efficiently removed by chemical coprecipitation, and so for removal of As(III) a pre-oxidation process has been recommended and generally adopted. The literature reports many studies in which an aqueous solution of either Fe(III) or Al(III) was the reagent that had been investigated for coprecipitation of As(V), and the mechanism of binding between the arsenic solute and the precipitated compound has also had considerable attention. There is argument as to whether Fe(III) or Al(III), used separately, is the most effective reagent for coprecipitation, and also concerning the optimal M(III):As(V) ratio for best removal. Many misconceptions have evolved from published work and this paper will address some of those and provide experimental comparisons in evidence. More importantly we report better results from using a mixed Fe(III)-Al(III) reagent for coprecipitation of As(V), rather than the individual Fe(III) or Al(III) solutions separately. The experiments reported here were confined to chloride systems.