Bioavailability and speciation of Cadmium in contaminated paddy soil as alleviated by biochar from co-pyrolysis of peanut shells and maize straw

Background: Biochar is an important material for remediation of Cd in contaminated paddy soils. However, different biochars have variable effects on bioavailability of Cd while single biochar can not properly amend immobilized Cd. Co-pyrolysis biochar was produced from peanut shell and maize straw in variable mass mixture ratios. The characteristics, properties and effects of co-pyrolysis biochars on amendments of Cd polluted paddy soil was evaluated. Results: : Our research revealed that yield, ash, elemental contents and specific surface area of co-pyrolysis biochars have variable amendment effects compared with single biochar. The co-pyrolysis biochar have produced rich oxygen-containing functional groups and crystal structure, especially 1P3M (co-pyrolysis produced from peanut shell and maize straw in mass ratios of 1:3). The addition of biochar has significantly enhanced pH and EC value, however, content of available Cd during incubation was significantly reduced compared with control treatment. The efficiency of biochars have reduced available Cd in order of 1P3M > M > 1P1M > 1P2M > 2P1M > 3P1M > P after incubation. The 1P3M was most effective in reducing CaCl 2 -extractable Cd concentration up to 43.97%. The BCR sequential extraction method has produced lowest exchangeable fraction Cd content and highest residual fraction Cd content in 1P3M among all biochar amended treatments. Conclusions: : It is concluded that 1P3M has a much greater potential to decreased the bioavailability of Cd in contaminated paddy soil. And 1P3M was highly effective for transporting Cd from soluble form to less toxic stable forms in polluted paddy soils.