A novel modified method for the efficient removal of Pb and Cd from wastewater by biochar: Enhanced the ion exchange and precipitation capacity

The purpose of this research was to improve the sorption ability of Pb and Cd by promoting the ion exchange and precipitation capacity of biochar. The adsorption performance and mechanisms of Pb and Cd in wastewater using coconut shell biochar modified with magnesium were investigated. After modification, the total adsorption capacity (Q_t) of Pb and Cd on Mg-coated biochar (MgBC400) increased by 20 and 30 times compared with the unmodified biochar (BC400), respectively. The removal of Pb and Cd to biochar was attributed to ion exchange (Q_e), mineral precipitation (Q_p), interaction with oxygen functional groups (OFGs) [(Q_f)], and metal-π electron coordination (Q_π). Compared with the BC400, the adsorption capacity of the four fractions of MgBC400 increased especially the ion exchange and precipitation. The Q_e values of MgBC400 were almost 49 and 59 times that of BC400 in the adsorption of Pb and Cd, respectively. The Q_p values of MgBC400 increased by 214.4 and 81.7 mg/g, respectively. Ion exchange and mineral precipitation dominated the adsorption of Pb and Cd by MgBC400.