Mechanisms of Pb Stabilization Using Modified Biochar in Coal Mining Areas in China

Modified biochar has become an efficient tool for modulating availability of heavy metals in soils. To identify a preferable material and explore the remediation mechanism of modified biochar for Pb-contaminated soil, H2O2-, HNO3-, KMnO4-, and CaCl2-modified biochars were applied at three ratios (1%, 2% and 3% w/w) to immobilize Pb in alkaline soil from coal-based solid waste dumps. Results showed that HNO3-BC exhibited abundant acidic functional groups, and KMnO4-BC had increased pH and CEC content. The application of modified biochars significantly altered soil Pb fractions. Compared with biochar and the control, the application of HNO3-BC and KMnO4-BC decreased acid-extractable Pb and increased the residual Pb fraction in soil. HNO3-BC was more effective than KMnO4-BC in promoting Pb transformation from labile fraction into stable fraction. The content of soil available Pb significantly decreased with increasing application ratio of HNO3-BC. The complexation between soil Pb and acidic functional groups on the biochar surface is considered the primary mechanism for reducing Pb mobility and availability in contaminated soils. This research demonstrated that HNO3-BC can serve as a potentially effective amendment for the remediation of heavy metal-contaminated alkaline soils in northern China.