Sortpion Of Heavy Metal And Organic Onto Sediment In Multi-solute System

Sorption of pollutants by sediments/soils is known to be a key process in respectto the transport and fate in the environmental systems. In this study, sorptionmechanism of heavy metal onto sediments/soils was reviewed, including many factorswhich influence the sorption; sorption behavior of surfactant and its influence on thesorption of organic were summarized; besides, the influence of surfactant and organicon the sorption of heavy metal was also evaluated.Considered the multi-solute systems in the natural environment, sorption ofcadmium and p-nitrophenol(PNP) onto sediment was investigated and the influence ofenvironmental factors was discussed based on the interactions between heavy metaland organic, organic and surfactant, heavy metal and surfactant. Conclusions aresummed up as follows:(1) In the multi-solute system, sorption of cadmium onto sediment presentedantagonistic effect. Antagonistic effect varied with different organics and surfactants,with a decreasing influence in the order: aniline＞phenol＞PNP; CPC＞TX-100＞SDBS.(2) In the multi-solute system containing Cd(NO₃)₂, CPC and PNP, influence ofion strength on the sorption of cadmium onto sediment was dependent on theconcentration of CPC. As the equibrium concentration was below 1CMC (criticalmicelle concentration), sorption of cadmium decreased with the increase of ionstreaghth. It is believed to be attributed by more cationic occupying the adsorptionsites at higher ion strenghth which lead to less sorption of cadmium. When theequibrium concentration was above 1CMC, sorption of cadmium increased with theincrease of ion streaghth due to less competitive effect of CPC at higher ion strenghth.(3) In the multi-solute system containing Pb(NO₃)₂, CPC and PNP, partitioning ofPNP in adsorbed surfactant layers and micelles decreased with increasing level ofPb(NO₃)₂ due primarily to competing for adsorption sites. Moreover, the influence of different metal ions (Pb²⁺, Cd²⁺, Zn²⁺) was examined and results indicated that thepresence of heavy metals inhibited the sorption of PNP in the order: Pb²⁺＞Cd²⁺＞Zn²⁺.The order of the competitive effect of the three heavy metals (Pb²⁺＞Cd²⁺＞Zn²⁺) wasin reasonable agreement with corresponding hydration energy (Pb²⁺= -1481 kJ mol^-1,Cd²⁺=-1807 kJ mol^-1, Zn²⁺=-2046 kJ mol^-1) as well as the hydrated radius(Pb²⁺=0.401 nm, Cd²⁺=0.426 nm, Zn²⁺=0.430 nm).(4) In the multi-solute system, the sorption of PNP increased with the increasingpH. This can be attributed to the presence of CPC and Pb(NO₃)₂. It is believed that themain reason for that was the larger sorption of CPC at higher pH allowing highersorption of PNP. At higher pH heavy metal competed less for the sorption sites withPNP. While the effect of different species on the sorption of PNP at different pHs wasnegligible.