Synchronization adsorption of Pb(Ⅱ) and Ce(Ⅲ) by biochar supported phosphate-doped ferrihydrite in aqueous solution: Adsorption efficiency and mechanisms

Abstract

Biochar facilitate the dispersion of nanoparticles and improve their adsorption capacity. Herein, we prepared a type of biochar-supported phosphate-doped ferrihydrite (P-FH@BC) for simultaneous uptake of Pb(II) and Ce(Ⅲ). P-FH@BC was prepared by mixing P-FH and biochar at different ratios, and the best ratio is 10:1. Acidic conditions inhibit the adsorption of Pb(Ⅱ) and Ce(Ⅲ) onto P-FH@BC, which was consistent with the result of zeta potential. The adsorption processes of Pb(Ⅱ) and Ce(Ⅲ) are competitive in the binary system. The pseudo-second-order kinetic can explain well the adsorption behavior of Pb(Ⅱ) and Ce(Ⅲ) on P-FH@BC, suggesting a complex chemical adsorption process. The adsorption of Pb(II) and Ce(III) by P-FH@BC included physical and chemical processes. The physical process was mainly contributed by electrostatic attraction and pore filling mechanism. The iron-containing groups, phosphorus-containing groups, oxygen-containing groups on the surface of P-FH@BC, as well as phosphate and iron oxide compounds mainly caused the chemical adsorption. Among them, phosphate, -OH and carbonate could combine with Pb and then form low solubility precipitates, such as Pb3(PO4)2, Pb(OH)2, etc., and iron-containing groups could adsorb Pb through ion exchange. The surface functional groups of P-FH@BC could also combine Pb through the surface complexation reaction. The chemisorption mechanism of Ce(III) by P-FH@BC is obviously different from that of Pb(Ⅱ). The adsorption of Ce(III) was mainly contributed by the phosphorus-containing groups on the surface of P-FH@BC due to the surface complexation. These results have important environmental implications for the simultaneous uptake of heavy metals and rare earth elements from solution.