Evaluation of performances of cadmium adsorption onto nano- and macro-biochar-treated alkaline sandy soil from aqueous solutions

In this study, the sorption kinetics and transport of cadmium (II) investigated in two sizes, nano (NBC) and macro (0.1–0.5 mm) (MBC) wood-derived biochar at 0, 0.5, 1, and 2% (w/w) dosages for various initial concentrations of Cd in an alkaline sandy soil using batch and column experiment (packed column under water-saturated condition). The results showed that the effects of biochar addition to sandy soil were related to the particle size and dosage. Batch experiment results indicated that maximum adsorption capacity was obtained by adding 2% of NBC. The pseudo-second-order kinetic model fitted the experimental data well (R ² = 0.989–1). The apparent adsorption rate of the power function kinetic model decreased 1.3-fold and 2.8-fold by adding 2% of MBC and NBC, respectively. Column experiments showed that increasing doses of MBC compared to NBC did not show the same trend in changes in sorption parameters with increasing initial concentration of Cd. In the column experiments, the effects of biochar particle size and dosage on the shape and period of the breakthrough curves were evident, but no specific trend was observed. The obtained sorption breakthrough curves data were successfully correlated with the Thomas, Yoon-Nelson, and Adam-Bohart models. The comparison of models revealed that the sensitivity of the parameters was nonlinearly affected by the initial concentration of Cd and biochar particle’s size and dosage. The findings suggest that facilitated Cd transport may not occur when appropriate dosage and sizes of biochar particles are applied to the soil, in such a way that extreme amounts of Cd adsorption retards Cd leakage to deeper layers.