Arsenate Adsorption on Different Fractions of Iron Oxides in the Paddy Soil from the Karst Region of China.

Adsorption of arsenate, a common soil contaminant, on natural occurring iron oxides controls arsenate adsorption on soils, especially on iron rich soils. However, soils contain multiple iron minerals and their contributions for arsenate adsorption on the bulk soil are unclear. In this study, Wenzel's sequential extraction procedure (SEP) was used to characterize different fractions of iron oxides in the paddy soils from Guangxi, China. Soils treated with different extractants in the SEP (i.e. soils contained different iron fractions) were used to study arsenate adsorption on different iron fractions in the soil. Langmuir model was used to assess arsenate adsorption capacities of those iron fractions. The results showed that though amorphous iron made up only 16% of the total iron in the soil, it accounted for 82% of the soil adsorption capacity. Besides, arsenate adsorption capacity on the soils could be estimated by linear addition of arsenate adsorption capacity on the amorphous iron oxides fraction and that on the other iron oxides fraction. This study implied a possibility to use iron fractions characterized by Wenzel's SEP to evaluate arsenate adsorption on the bulk soils.