Qualitative and quantitative correlation of physicochemical characteristics and lead sorption behaviors of crop residue-derived chars.

This study investigated the key physicochemical characteristics of char that control its ability to absorb Pb2+. Three type of crop residue-derived chars and their ball milled powder were characterized using multiple approaches. The Pb2+ sorption mechanisms of biochar were caused mainly by coprecipitation reactions, which were governed by ionic minerals on chars instead of mineral crystallization (e.g., SiO2 and Al2O3), while coprecipitation reactions and π electronic interaction were the dominant mechanisms of activated carbon. Pearson analysis showed that adsorption quantity (Q) highly correlated with the cation exchange capacity (CEC) (P < 0.01)/oxygen functional groups (OFGs) (P < 0.05) and Q closely correlated with coprecipitation amount (P < 0.01)/complexation amount (P < 0.01). Linear regression equations of sorption amount and CEC (R2 ＞ 0.8)/OFGs (R2 ＞ 0.7) were established. CEC and OFGs of chars are the key factors controlled Pb2+ sorption. These results may promote the development of low-cost, engineered biochar with superior sorption qualities for environmental remediation.