Effect of phenanthrene on adsorption of Cd on Xiangjiang River sediments.

Two synthetic water samples,one contaminated by cadmium(Cd) and phenanthrene(phe),and the other contaminated by Cd,were prepared.The effects of phe on the dynamics and thermodynamics of adsorption of Cd on Xiangjiang River sediments in both water samples were investigated.The influences of pH,mass concentration of sediment and mass concentration of phe on the adsorption of Cd were also studied.The results showed that the Langmuir equation described the adsorption isotherms well,with a correlation coefficient up to more than 0.99,whether phe existed or not.The Lagrangian second-order dynamic equation described the adsorption dynamics well,with a correlation coefficient of about 1.This indicated that the adsorption of Cd on Xiangjiang River sediments was monolayer adsorption,and that the dominant mechanism was chemical adsorption in both water samples.Rapid adsorption played the main role in the adsorption of Cd on Xiangjiang River sediments.The adsorption capacity reduced and the desorption ratio increased when phe existed.The degree of the effect of phe on the adsorption of Cd on Xiangjiang River sediments decreased when pH increased.The adsorbance of Cd reduced with the increase of phe concentration.The effect of phe on the adsorption of Cd on Xiangjiang River sediments is due to two reasons: one is competition on the particulate's surface between phe and Cd;the other is the particulate's polar groups being reduced as a result of the combination of methanolized phe and sediment particulates.