Adsorption of cadmium and lead ions by phosphoric acid-modified biochar generated from chicken feather: Selective adsorption and influence of dissolved organic matter.

To improve the adsorption efficiency, a H3PO4-modified biochar (CFCP) was prepared using chicken feather and applied to Cd2+ and Pb2+ adsorption. The pseudo-second-order model could explain the Cd2+ and Pb2+ adsorption behavior. CFCP had faster adsorption rate than non-modified biochar (CFC2). The Langmuir and Freundlich isotherm could better describe the Cd2+ and Pb2+ adsorption, respectively. The value of qm for Cd2+ adsorption and KF for Pb2+ adsorption by CFCP was 7.84 mg·g-1 and 24.41 mg1-(1/n)·L1/n·g-1, which was 1.38 and 5.41 times of the corresponding results of CFC2. Relative to Cd2+, Pb2+ was selectively adsorbed by biochars in the binary metal system. Phosphate precipitation explained in part the selective adsorption of Pb2+. Proline, glucose, and pH (4-6) had little influence on Cd2+ and Pb2+ adsorption. Electrostatic interaction, precipitation, and O-H bonds were the primary adsorption mechanisms. The increased N-containing heterocycles of CFCP accounted for the increased Cd2+ and Pb2+ adsorption.