Adsorption and Transport of As (V) in Soil Columns:Effect of As Concentration, pH and Sediment Properties.

It has been proposed that ground water contaminated with low concentrations of As (V) be remediated by infiltration and recharge into infiltration basins using the subsurface materials to adsorb the metal. This low cost remediation scheme allows for production of water that meets the drinking water quality criteria. In order to investigate the feasibility of the proposal, we examined the adsorption of As(V) on three subsurface materials sediments as related to As concentration and pH in batch studies. We then modeled the data using the constant capacitance model. We next conducted leaching experiments in the laboratory at two pH’s (6 and 8) and two As concentrations (30 and 300 µg/L) on the three materials. We applied up to 55 pore volumes of solution into the columns and measured effluent pH and As and tracer concentrations. Total As was measured with ICP MS to below 0.5 µg/L.  Effluent concentrations remained in the range of 1-2 µg/L, except with the coarsest material (gravel) where there was some breakthrough after 50 pore volumes when applying the 300 µg/L solution.  At the end of the experiment we sectioned the column and performed sequential extractions. Most As was tightly held in adsorbed form but there was transformation to more tightly bound forms.  There was no pH effect on adsorption or transport. We conclude that even the coarse grained materials having somewhat less adsorption capacity were effective for remediation, as adsorption is primarily occurring on oxide surface grain coatings.