Modeling arsenic(III) adsorption and heterogeneous oxidation kinetics in soils

Arsenite [As(III)] is a soluble and toxic species of arsenic that can be in troduced into soil by geothermal waters, mining activities, irrigation prac tices, and disposal of industrial wastes. We determined the rates of As(In) adsorption, and subsequent oxidation to arsenate [As(V)] in aerobic soil-w ater suspensions using four California soils, The rate of As(III) adsorptio n on the soils was closely dependent on soil properties that reflect the re activity of mineral surfaces including citrate-dithionite (CD) extractable metals, soil texture, specific surface area, and pH, Heterogeneous oxidatio n of As(III) to As(V) was observed in all soils studied. The recovery of As (V) from As(III)treated soils was dependent on levels of oxalate-extractabl e Mn and soil texture, After derivation of rate equations to describe the c hanges in soluble and recoverable As(III) and As(V) in soil suspensions, so il property measurements were used to normalize the empirically derived rat e constants for three soils. The fourth soil, which had substantially diffe rent soil properties from the other three soils, was used to independently test the derived soil property-normalized model. The soil property-normaliz ed consecutive reaction model gave a satisfactory description of the trends seen in the experimental data for all four soils. Understanding the effect s of soil properties on the kinetics of chemical reactions of As(III) and A s(V) in soils will be essential to development of quantitative models for p redicting the mobility of As in the field.