Cadmium Immobilization Potential of Rice Straw-Derived Biochar, Zeolite and Rock Phosphate: Extraction Techniques and Adsorption Mechanism.

Heavy metal contamination in agricultural soils has become a serious environmental concern due to their generally high mobility and toxic effects on plants and food security. An incubation study was conducted to assess the effectiveness of biochar (BC), zeolite (ZE) and rock phosphate (RP) stabilizers on the immobilization of cadmium (Cd) in contaminated soils. Various extraction techniques were carried out: a sequential extraction procedure, the European Community Bureau of Reference (BCR), the toxicity characteristics leaching procedure (TCLP) and extraction with ammonium nitrate. In addition, Cd adsorption by these materials was observed using Langmuir and Freundlich isotherms. The results showed that with an increase in soil pH the exchangeable fraction of Cd in soil was significantly reduced by 28%-29.4%, 9%-13% and 4%-14% for BC, ZE, and RP, respectively. According to the Langmuir adsorption isotherm, BC-amended soil showed a higher adsorption capacity (Qm) of Cd from 8.38 to 19.85 mg g-1. Overall, BC offered better results when compared to other amendments.