[Lead Removal from Water by Calcium-containing Biochar with Saturated Phosphate]

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 CO₃^2- and PO₄^2- 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.