Arsenic adsorption by soils and iron-oxide-coated sand: kinetics and reversibility

Arsenic has recently received increasing attention due to its high toxicity and to the possible risks for human and environmental health associated with As-polluted soils. The present work deals with the kinetics and reversibility of As sorption by Fe-oxide-coated sand (IOCS) and soils with different chemical and physical characteristics. Soils and IOCS were equilibrated for five different periods of time with solutions containing As (III) and/or (V) in order to study the kinetics of As adsorption. After 1, 10 and 30 days of equilibration soils and IOCS were sequentially extracted to assess the effect of aging on the binding forms of As. The kinetics of arsenite and arsenate adsorption varied among the soils as a result of differential soil characteristics. The conversion of As to less mobile forms was demonstrated using a sequential extraction. The amount of As extracted with weaker extractants decreased with time whereas the amount of As in more recalcitrant fractions increased. This conversion is expected to render As less mobile and toxic with time after addition to the soil.