Comparative evaluation of arsenate sorption–desorption in two soils of North India

A sandy loam (Typic Ustochrept) and a clayey (Typic Hapludalf) soil from two north Indian states, Punjab and Himachal Pradesh, respectively, were used to study sorption–desorption behaviour of arsenate. Arsenate sorption by the soils was studied from a range of added concentrations (50–100 mg arsenate kg⁻¹) in the presence of background electrolyte, 0.01 M KNO₃. Arsenate sorption was found to increase with each increment in added arsenate concentration in both the soils. However, the magnitude of sorbed arsenate decreased. The sorption was rapid initially followed by gradual retention behaviour. The amount and pattern of arsenate sorbed over a period of time (2–512 h) differed between the two soils. The sorption was higher and quicker by clayey soil as compared to sandy loam soil, which could be due to difference in their pH, AEC, organic matter, Fe and Mn oxide content. Arsenate sorption data were well explained by Langmuir and Freundlich sorption isotherms. Desorption of arsenate was carried out by six successive washings with arsenate free 0.01 M KNO₃ solution. At all levels of added arsenate, most of the sorbed arsenate could not be desorbed back into the solution and a marked hysteresis between arsenate sorption and desorption isotherms was observed in both soils which became greater with increasing reaction period. Relatively lesser amount of arsenate could be desorbed back from clayey soil than from sandy loam soil.