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It has been found that Pb and Cd can be gradually purified during their transportation in rivers and that the rate of purification for Pb is much greater than that of Cd,Such process is not only closely related to the degree of water dilution and the properties of Pb and Cd themselves, but also to the existing ligands, oxidation-reduction conditions, colloids, pH and other factors in the aquatic environment. Suspended particles and river-bed sediments have a strong ability of adsorption and purification with respect to Pb and Cd. This ability shows a positive correlation with the composition of clay in sediments on the river bed, but a negative correlation with the grain-size of quartz particles. our results indicate that both the adsorption and possible desorption of Pb and Cd in river-bed sediments and suspended particles may be highly responsible for the variations in Pb and Cd concentrations in aquatic environments. The dynamic adsorptiondesorption balance of Pb and Cd between riverbed sedimeuts and water varies with pH.It may be favorable for the purification of Pb and Cd in aquatic environments if pH is adjusted to slightly alkaline within the tolerance of environmental capacity. 相似文献
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