Effects of biochar on heavy metals migration and fractions changes with different soil types in column experiments

Effects of biochar on different soil types were studied in soil column experiments. The results showed that the biochar decreased filtrate heavy metals concentration by 89.0% to 95.7% (Cd) and 93.2% to 99.3% (Pb) compared with the control. The biochar application changed 2.3% to 9.84% of the exchangeable Cd fraction Pb to residual fractions, so the bioavailable Cd and Pb were reduced by 4.48% to 10.69% (Cd) and 11.74% to 16.42% (Pb) in surface soil (0 to 4 cm). Through increasing the soil ratio, the concentration of bioavailability of Cd and Pb was decreased 13.84% to 16.15% and 4.02% to 13.40% in 4 to 8 cm soil. With sandy soil, the application of biochar effectively reduced the down migration of heavy metals, and accomplished the conversion of 100.0% and 95% exchangeable Cd and Pb fractions into 13.1 to 43.9% residual Cd and 11.6 to 100.0% residual Pb. The SOM and pH also increased 1.2 to 2.3 g kg-1 and 0.01 to 0.31 with biochar application. The biochar effectively increased the SOM content, and stabilized heavy metals, then reduced the migration of Cd and Pb.