Arsenic of Adsorption Characteristics in Taiwan Soils

Abstract

In soil environment, various forms of solid-phase arsenic of total amount of arsenic and the aqueous form of arsenic in soil solution make a thermodynamic equilibrium system. The uptake of aqueous arsenic by crop roots results in the shift of this equilibrium system. The purpose of this research was thus to investigate the adsorption characteristics of aqueous As (III) and As (V) in Taiwan soils. The results from the adsorption batch experiment showed that the adsorption capability of the soils increased with increasing amounts of Fe, Mn and Al oxides. In addition, the adsorption of As (V) was higher than As (III) by the same soil. Because of the competition between phosphate and arsenite/ arsenate anions for the adsorption sites on the soils, the samples with high amount of bound phosphate were less capable to adsorb aqueous arsenic. The desorption of arsenic occurred within 2-3 hr when the soils were submerged in water. This contributed to the increase of concentration of aqueous arsenic in the reaction systems. In the batch experiment, the kinetics analyses of the adsorption of As (III) and As (V) by the soils showed that the main reaction was of zero order in 0 to 24 hr and of the 3rd order in some few reaction periods.