Abstract:Effects of phosphorus (P) and citric acid (CA) on Pb2+ adsorption by goethite and kaolinite were studied through a batch isothermal equilibrium experiment and Zeta potential analysis. Results show that the Pb2+ adsorption by goethite and kaolinite rose with rising citric acid concentration and peaked when citric acid concentration reached 0.5 mmol L-1. The effect of citric acid was enhanced to a varying extent by the presence of phosphorous regardless of concentration. With rising P concentration, Pb sorption by the two minerals increased and leveled off when P concentration reached 1 mmol L-1 and 0.6 mmol L-1for goethite and kaolinite, respectively. When citric acid was spiked in addition to phosphorus, Pb sorption by the two minerals increased with rising citric acid concentration added, which indicates that phosphorous and citric acid would jointly enhance lead sorption by the minerals. In the kaolinite system, the addition of phosphorous and/or citric acid moved the Zeta potential-pH curve towards negative, displaying an order of 1.0 mmol L-1 P +0.5 mmol L-1CA > 0.5 mmol L-1CA > 1.0 mmol L-1P, in terms of intensity of the effect, which indicates that the increased negative charges on the surface of kaolinite are responsible partially for the increased electrostatic adsorption of Pb2+. Both P and citric acid decreased Zeta potential of goethite significantly, and Zeta potential did not vary much with rising pH, which indicates that both phosphorous and citric acid increase specific adsorption Pb mainly by getting adsorbed on the surface of goethite.