Arsenate displacement from fly ash in amended soils

Arsenic (As) is the biggest environment contaminant in most of the soils wh ere fly ash is applied. Usually, it is not mobile and strongly adsorbed on to soil particles. However, in gypsum and phosphorus amended soils As may b e much more mobile. A study in repacked columns was conducted to determine whether or not As becomes mobile when Ca(H2PO4)(2) and CaSO4 are used as le aching solutions, and to compare the competitive interactions between PO4-A sO4 and SO4-AsO4. Arsenic concentration in leachate was found to be approxi mately ten times greater when Ca(H2PO4)(2) was used to leach the columns as compared to CaSO4. A maximum concentration of 800 mu g As L-1 was found in the leachate in this case, which is much higher than the groundwater limit of 50 mu g L-1 for drinking water established by the United States Environ mental Protection Agency. In fly ash, the portion of arsenate non-specifica lly adsorbed is believed to be much lower than that of specifically adsorbe d. Sulfate anions were able to displace only non-specifically adsorbed arse nate. In this case the concentration of As in leachate was found to be with in acceptable limits. On the other hand, phosphate can compete with arsenat e for all available adsorption sites, non-specific and specific. Phosphate displacement of both forms of arsenates increases As mobility in both contr ol and fly ash treatments.