Calcium-containing biochar （ES-BC） was prepared by pyrolyzing eggshell and kitchen wastes， and the ES-BC composite was used to remove phosphate （marked as ES-BC/P）. Based on the high affinity of phosphate and carbonate to lead， the ES-BC/P was then used to remove lead from the water. The results showed that， in the appropriate dosage， ES-BC/P could remove lead efficiently at different initial concentrations （1-100 mg·L-1）， and the removal efficiency could reach to 99%. Meanwhile， the release of phosphorus could be ignored after the reaction. As ES-BC/P was alkaline， and the lead-containing solution was weakly acidic， the addition of ES-BC/P could adjust the pH of the system automatically. The reaction kinetics and isotherm experiments showed that the lead removal by ES-BC/P was mainly monolayer chemisorption with a maximum adsorption capacity of 493.12 mg·g-1 （318 K）. The characterization results showed that lead was mainly removed through the ion exchanges of Pb2+ in the solution with Ca2+ in ES-BC/P. Then， the Pb2+ combined with CO32- and PO42- to form many precipitates， including Pb5（PO4）3OH， Pb10（PO4）6（OH）2， PbCO3， and Pb3（CO3）2（OH）2. In summary， the ES-BC/P material could achieve the efficient removal of lead from the water， thereby realizing the resource utilization of the wastes.
Keywords: biochar; calcium carbonate; lead removal; phosphate; recycling.