Study On The Adsorption Of Cd And Phenanthrene On Xiangjiang River Sediments Under The Condition Of The Combined Pollution

Heavy metals and polycyclic aromatic hydrocarbons are the two types of high toxic pollutants which can be found at the same time in contaminated environment. Hunan Province is abundant in nonferrous metals. Polycyclic aromatic hydrocarbons and heavy metals often enter environment along with the discharge of exhaust gas waste water and the eluviation of metallurgical residues and tailings. Furthermore, they enter Xiangjiang River along with surface runoff and atmospheric deposition forming combined pollution, which have an important influence on water quality. For a long time, many studies from home and abroad have focused on the individual pollution resulted by heavy metals or polycyclic aromatic hydrocarbons, and also there are some works focusing on the effect of the combined pollution. But little information about the fundamental law of adsorption of the two contaminants on Xiangjiang River sediment when they co-exist has been found. Cd and the phe were selected as representative substance in this study, and the study mainly focused on the adsorption law of the combined pollution on sediment, which can provide some basic datum for controlling pollution and the evaluation and prediction of the migration and the fate of the two of pollutants in water environment.First, the characteristics of sediments from different reach of Xiangjiang River were analyzed. Second,the adsorption characteristics of phe on XiangJiang River sediments when Cd existed were investigated. The influences of the pH value, the difference of sediments, the concentration of Cd and the existing of microbes on the adsorption of phe were also studied. The results showed that the influence of the existing of Cd on the laws of the adsorption dynamics and the adsorption thermodynamics of phe on XiangJiang River sediments was small, and rapid adsorption played the main role in the adsorption of phe on XiangJiang River sediments. Freundlich equation described the adsorption isotherms well which indicated that the adsorption of phe on XiangJiang River sediments was multi-molecular layer adsorption. The adsorption capacity of phe on XiangJiang River sediments increased when Cd existed,which was due to the role of"bridge"of Cd, because it could make more DOM be adsorbed by sediment, thereby the organic content in the sediments increased resulting in more phe being adsorped. The linear characteristic of the adsorption curve of phe on XiangJiang River sediments became more and more obvious with the decrease of sediments concentration and the adsorption of phe was mainly a distribution function when the concentration of sediments was lower. The correlation of the thermodynamics datum of adsorption and Freundlich equation decreased with the increase of sediments concentration, which indicated that the adsorption of phe on XiangJiang River sediments became more complex when sediments concentration increased. The carbon content of sediments not only affected the adsorption process but also affected the desorption process. The adsorbance of phe decreased with the increase of sediments concentration. The adsorption effect of XiangJiang River sediment on phe was strongest when pH at 5 and 4, respectively, when Cd existed or not. Inoculation of polycyclic aromatic hydrocarbons resistant microbes accelerated the adsorption of phe on Xiangjiang River sediments.Finally, the adsorption characteristics of Cd on XiangJiang River sediments were investigated when phe existed. The influences of the pH value, the concentration of sediment and the concentration of phe on the adsorption of Cd were also studied. The results showed that the Langmuir equation described the adsorption isotherms well whether the phe existed or not, and that the Lagrangian second-order dynamic equation described the adsorption dynamics well, which indicated that the adsorption of Cd on XiangJiang River sediments was monolayer adsorption and that the dominant mechanisms was chemical adorption. 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 value increase. The adsorbance of Cd reduced with the increase of phe concentration. The adsorbance of Cd increased with the increase of sediments concentration. Effect of phe on adsorption of Cd on XiangJiang River sediments due to two reasons: one is the competition on the particulate's surface between phe and Cd; the other is the particulate's polar groups being reduced resulted from the combination of methanolized phe and sediment particulates.To sum up the above conclusions, the laws of the dynamics and thermodynamics of adsorption of phe and Cd on XiangJiang River sediments had little change when they co-existed. But Cd contamination to some extent enhanced the adsorption of phe on the sediments while phe contamination to some extent weakened the adsorption of Cd on the sediments.