磷和柠檬酸共存对高岭石和针铁矿吸附铅的影响

通过平衡吸附试验及矿物电动电位(Zeta电位)的变化分析,研究了磷(P)和柠檬酸(CA)共存对针铁矿和高岭石吸附铅的影响。结果表明:(1)针铁矿和高岭石对铅的吸附量随柠檬酸浓度的升高呈现"峰形"曲线变化,铅吸附量达到峰值的柠檬酸浓度均为0.5 mmol L~(-1),不同浓度磷存在下柠檬酸对矿物吸附Pb2+量有不同程度增加。(2)随着磷添加浓度的增加,两种矿物对铅吸附量均呈增加趋势,磷添加浓度分别为1 mmol L~(-1)和0.6 mmol L~(-1)时,针铁矿和高岭石吸附铅量达到平衡;当处理中添加不同浓度柠檬酸,两种矿物均表现为对铅的吸附量增加,且随着柠檬酸浓度增加促进铅吸附的作用增强,说明在磷及试验浓度柠檬酸存在下促进了矿物对铅的吸附。(3)高岭石体系中,加入磷或(和)柠檬酸后,Zeta电位-pH曲线向负值方向位移,降低程度大小顺序为1.0 mmol L~(-1) P+0.5mmol L~(-1) CA0.5 mmol L~(-1) CA1.0 mmol L~(-1) P,说明高岭石表面增加的负电荷也部分增加了其对铅的电性吸附;添加磷和柠檬酸处理针铁矿的Zeta电位显著降低,且随着体系pH的升高其Zeta电位没有明显变化,表明磷和柠檬酸均主要是通过吸附到针铁矿表面而增加对铅的专性吸附。

Effects of Phosphorus and Citric Acid on Pb2+ Adsorption by Kaolinite and Goethite

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.