The effects of biochar and rice husk on adsorption and desorption of cadmium on to soils with different water conditions (upland and saturated)

Hard wood derived biochar (BCH) and rice husk (RCH) were applied to soils having upland and saturated conditions to investigate their effects on adsorption and desorption of Cd by conducting incubation and batch experiments. The results obtained from the experiments indicated that BCH increased Cd sorption by 59-71% onto saturated soil (SS), while by 57-84% onto upland soil (US). The application of RCH also increased the sorption of Cd onto the soils under both water conditions but the increases were less as compared to BCH. With RCH application, 21-41% increases in sorption of Cd on SS and 38-54% on US soils were observed. The Langmuir equation fitted sorption of Cd better than Freundlich with R² > 0.95 for all selected treatments. Both electrostatic and non-electrostatic mechanisms played their important roles in the adsorption of Cd in the amended soils. BCH enhanced non-electrostatic adsorption as compared to RCH and thus control and induced greater specific adsorption capacity. High desorption percentage of pre-adsorbed Cd on soils were observed both with and without amendments. Decreases in desorption percentage of pre-adsorbed Cd on both soils were observed with BCH with a highest decrease on SS (39%). The application of selected amendments into different soils increased Cd adsorption of soils through both electrostatic and non-electrostatic mechanisms and the contribution of both the mechanisms varied with types of amendments and soil conditions. BCH material showed promising results in Cd adsorption as compared to RCH for different selected soils and conditions but cost-benefit analysis is needed in field condition.