The removal of arsenic from aqueous solution by coprecipitation with iron (III)

In treating hydrometallurgical solutions and waste streams for the removal of arsenic, the use of coprecipitation with Fe(III) has been specified by the U.S. EPA as the Best Demonstrated Available Technology. This technology has been widely adopted over the last century, and developments have been well reviewed. This paper is aimed at clarifying a number of uncertainties that result from previously published work by many authors. The clarification will include a discussion of the importance of Fe/As mole ratio, initial arsenic concentration, arsenic valence state, the effect of mixed arsenic valence states, system agitation rate, and possible modifications to the ferrihydrite structure on the effectiveness of arsenic removal. A comparison of the effectiveness of arsenic removal by ferrihydrite coprecipitation, adsorption during post precipitation and on granulated ferrihydrite will be presented. Also, factors effecting ferrihydrite long term stability will be discussed.