How Does the Use of Biochar, Phosphate, Calcite, and Biosolids Affect the Kinetics of Cadmium Release in Contaminated Soil?

Cadmium (Cd) is a hazardous heavy metal that poses several problems to human health and the environment requiring remediation to reduce such risks. In situ remediation is a promising, low-cost strategy for immobilizing heavy metals in soil. Using soil materials from a natural forest and from a mining area near the forest, Cd released kinetics (by the stirred flow method) combined with sequential chemical extraction as a function of the application of rates of biochar, phosphate, calcite, and biosolids were investigated through a series of laboratory experiments. Among the amendments, biochar and biosolids were more effective in reducing Cd desorption kinetics in forest soil than in mine soil. Both treatments increased the Cd associated with organic matter (OM), which suggests that part of the Cd was immobilized by the organic compounds that were applied to the soil. Phosphate application to both soils reduced Cd desorption kinetics. Column leaching carried out using the mine soil showed that a quarter and a half of the phosphorus (P) rate increased Cd leaching, while the higher rate decreased Cd leaching compared to untreated forest soil. Treatment with calcite was more effective in decreasing desorption kinetics of Cd in the mine soil in the initial time period (30 min), while the same was observed in the forest soil only after 120 min. In both soils, the Cd associated with OM increased after the addition of calcite as a result of the increase in the negative charge on the surfaces of the OM.