Arsenite In Soils: Analytical Determination, Sorption-Desorption Reactions And Sorption Kinetics (Elevich Equation, Differential Pulse, Polarography).

A technique was developed for the determination of total arsenic (As) in soil using differential pulse polarography. Soil samples were digested with a combination of HNO(,3) and H(,2)SO(,4). Total As was determined in M HCl after reduction of As(V) to As(III) with hydrazine sulfate. Soil and fly ash standards were analyzed by this method and agreement within one standard deviation between replicates was obtained. Approximately 99% recovery of As was obtained from spiked soil samples. Differential pulse polarography is also quite useful for the rapid determination of arsenite in solution during studies of As sorption - desorption by soils. A linear form of the Freundlich isotherm was used to describe arsenite sorption by the A and B horizons of five West Virginia soils. Arsenite sorption conformed to the Freundlich isotherm over the entire concentration range for all the soils. Simple correlation coefficients and multiple regression equations were used to relate soil properties to parameters of the Freundlich equation. Iron oxide %, pH and OC% were the soil properties most closely related to parameters of arsenite sorption. The rate of arsenite sorption by the A and B horizons of an Upshur soil was investigated. The rate of arsenite sorption was rapid initially and decreased with time. A modified form of the Freundlich equation was used to explain the arsenite sorption rate data. Arsenite desorption was not reversible, only a small amount of the adsorbed arsenite was released after the five desorption steps. The modified Freundlich equation was also used to describe arsenite desorption rate. Simple and multiple regression calculations indicated that iron oxides and pH played an important role in regulating the rate of arsenite desorption by the investigated soils. The sorption rate of arsenite by 10 surface and subsurface horizons was investigated. An Elovich type equation and a modified Freundlich equation were used to describe the kinetics of the arsenite sorption process. Both equations successfully describe arsenite sorption rates. However, the modified Freundlich equation proved to be superior when both coefficients of determinations (R(\u272)) and standard errors of estimate (SE) were considered. The SE values from the modified Freundlich equation were consistently lower than those from the Elovich equation. Modified Freundlich equation parameters were regressed against soil chemical and physical properties to indicate possible sorption mechanisms and to identify soil properties that could serve as predictors of arsenite sorption. The regression equations indicated that iron oxides and pH were the main soil properties controlling arsenite sorption rate. A mechanism involving specific adsorption of arsenite with binuclear bridging to soil iron oxides would be consistent with findings for other oxyanions