Speciation, adsorption, and redox transformation of arsenite and arsenate in soils exhibiting a range in arsenic retention capacity.

摘要

The first of three studies in this dissertation describes the development of a suppressed ion chromatographic (SIC) technique for the direct, simultaneous determination of the As and Se oxyanions in soil solution. Baseline resolution of 1 mg L{dollar}sp{lcub}-1{rcub}{dollar} each of arsenite, arsenate, selenite, and selenate was achieved in the presence of 50 mg L{dollar}sp{lcub}-1{rcub}{dollar} each of F, Cl, NO{dollar}sb3{dollar}-N, SO{dollar}sb4{dollar}-S, and PO{dollar}sb4{dollar}-P. Detection limits ranged from 0.026 mg L{dollar}sp{lcub}-1{rcub}{dollar} for selenite to 0.120 mg L{dollar}sp{lcub}-1{rcub}{dollar} for arsenate. The accuracy of the SIC technique was verified by comparison to two spectroscopic methods.; The objective of the second study was to investigate the suitability of linear-plateau regression analysis for statistical evaluation of As adsorption data. The time required to reach the adsorption plateau depended on soil characteristics and As species. Identification of the adsorption plateau by the linear-plateau model allowed comparison of adsorption rates and maxima through use of analysis of covariance and least significant difference procedures.; The objective of the third study was to investigate the rates of reduction of arsenite and arsenate in flooded soils. Two soils, exhibiting a range in As adsorption capacity, were amended with arsenite or arsenate and flooded. Changes in solution chemistry (Eh, pH, and soluble Fe, Mn, arsenite, and arsenate) were determined as a function of flooding period. Adsorption processes controlled the solubility of arsenite and arsenate during the initial stages of flooding. When anaerobic conditions were achieved, dissolution of Fe and Mn oxyhydroxides occurred causing desorption of arsenite and arsenate. Once desorbed, arsenate was rapidly reduced to arsenite. A linear relationship was obtained for first-order plots of arsenite and arsenate reduction data. Furthermore, the rate of reduction of these As species appeared to be influenced by the As adsorption capacity of the soil. Rate constants were lower and half-lives were longer for the reduction of both arsenite and arsenate in the soil exhibiting high adsorption capacity.