Arsenic removal from aqueous solution via ferrihydrite crystallization control.

Removal of arsenate anion from aqueous solution by coprecipitation with ferrihydrite has been studied under conditions in which the Fe/As ratio is maintained at a constant level, while the degree of supersaturation with respect to the iron oxide precipitate is varied. An Fe/As ratio of 12 was chosen, and supersaturation was controlled by varying the iron concentration or the pH. The relationship between supersaturation and arsenic removal was found to follow an exponential curve, with greater arsenic removal occurring at higher supersaturation ratios for each of the pH values tested.