Quantitative contribution of dissolution-driven precipitation to Pb(II) removal by biochars during adsorption process

Biochar (BC) has been widely used for the lead (Pb(II)) immobilization in soil remediation. However, the mechanisms of dissolution-driven removal of Pb(II) by BC are still poorly understood. Herein, Pb(II) removal was investigated by differentiating BC- and dissolved organic carbon (DOC)-systems. As per the kinetics and isotherms, Pb(II) removal ranged from 31.11% to 80.92% in BC-system. This removal process was significantly influenced by dissolution-driven precipitation which contributed from 23.42% to 84.03% in DOC-system. During Pb(II) removal, an obvious reduction was observed in the released inorganic anions including carbonate (CO 3 2− ), sulfate (SO 4 2− ), and phosphate (PO 4 3− ). The CO 3 2− was a predominant contributor to facilitate Pb(II) precipitation. X-ray diffraction further confirmed the formation of cerussite (PbCO 3 ) and anglesite (PbSO 4 ) on BC surface after Pb(II) removal. Moreover, the decreased fluorescence responses of humic-like and fulvic-like substances were detected in DOC-system with the addition of Pb(II). At the same anion concentration, the enhanced Pb(II) amount was removed with increasing DOC concentration from 1 mg·L − 1 to 5 mg·L − 1 . These results indicated that released DOC exerted a significant contribution on Pb(II) precipitation due to its coagulation effect. This research provides mechanistic insights into the contributions of adsorption and dissolution-driven precipitation in overall Pb(II) removal through BC application.