Adsorption of Pb2+ from aqueous solution by walnut shell powder
核桃壳粉对水溶液中Pb2＋的吸附

In this study, the adsorption of Pb2+ from aqueous solution by walnut shell powder was investigated. The effect of experimental parameters, such as sorbent size, dosage, pH and initial Pb2+ concentration,as well as adsorption thermodynamics and kinetics were also examined. The results show that the removal efficiency increased with the decreasing sorbent size, increasing sorbent dosage and initial Pb2+ concentration. Under optimized conditions, 0~0.3 mm 15 g/L sorbent could remove 96.98% of Pb2+from 50 mL 50 mg/L Pb2+ solution at pH=5 and 298 K. The experimental data closely followed Sips isotherms, with adsorption capacity of 18.25, 18.27 and 20.94 mg/g at 283, 293 and 303 K, respectively. The overall adsorption process was exothermic, entropy reduced and spontaneous. The adsorption kinetics followed the pseudo-second order model, and the rate constant decreased with the increasing temperature. The adsorption equilibrium could be reached within 90 and 120 min at 293 and 303 K, respectively. Combined with FTIR and SEM methods, the process of adsorption Pb2+ on walnut shell powder was found to be complex and dominated by physical adsorption, accompanied with minor ion exchange, chelation and intra-particle diffusion process.