Study on Adsorption Performance and Mechanism of Peanut Shell Biochar for Pb^{2 +} and Cd^{2 +} in Water

Biochar was prepared by high temperature pyrolysis using the peanut shell(a agricultural waste) as raw material in this research. The emphasis was put on investigating the removal performance of Pb^{2 +} and Cd^{2 +} from single metal ions solution and mixed metal ions solution by peanut shell biochar(PSC), respectively, and then the mechanism of the removal process was revealed by XRD analysis. The results showed that PSC obtained at 700℃ had high specific surface area and pore volume. Meanwhile, it exhibited excellent removal capability for the lead and cadmium solution with initial pH of 3.5–5. Moreover, when the conditions were 150 mg/L initial concentration, initial solution pH 4, contact time 24h and the solid-liquid ratio 1∶100, the removal rate of Cd^{2 +} by PSC was more than 80%, and that of Pb^{2 +} reached 99.04%. Furthermore, as the 2 ions coexisted in the solution, Cd^{2 +} has little effect on the removal rate of Pb^{2 +} , however, Pb^{2 +} could significantly inhibit the adsorption of Cd^{2 +} on the PSC. The equilibrium adsorption time of PSC for Pb^{2 +} and Cd^{2 +} in water was 960min. Besides, the adsorption process satisfied the pseudo-second-order kinetic equation and the Freundlich isotherm model, and the equilibrium adsorption capacities of Pb^{2 +} and Cd^{2 +} could reach 57.23 mg/g and 17.75 mg/g. Then, it was revealed that the removal of both metal ions by PSC was mainly relying on chemical precipitation, involving the formation of hydroxide precipitation and the conversion of hydroxide to carbonate partially.