Study Of The Environmental Geochemical Behavior Of Cd And Other Heavy Metals In The Changjiang River And Typical Soil In It’s Basin

Heavy metals are considered a kind of serious pollutions in nature because of their toxicity, bioaccumulation and persistence. The pollution of heavy metals to enviromment is affected by the speciation of heavy metals in environment, the mechanism of heavy metals in soil/sediment media and the migration rate of heavy metals in soil. Therefore the understanding of the distribution, enrichment, source of heavy metals in environment and valuation the ecological damage of heavy metals in environment can provide a theoretical basis for prevention and treatment of heavy metal pollution in environment. In this paper, the geochemistry of Cd and other metals in water and sediment of the Changjiang River have been studied, firstly. The research mainly focused on analysis of the concentration levels and spatial variablity of Cd and other metals in water and sediment of the Changjiang River. At the same time, the source and pollution of heavy metals in water and sediment of the Changjiang River were studied through statistical analysis. Secondly, the soil and sediment of the Changjiang River were the research objects. The mechanism, migration process, the release characteristics and the speciation transformation of heavy metal Cd and Pb in soil and sediment were studied by combining static adsorption experiments, competitive adsorption experiments, dynamic soil column leaching experiments and release experiments of heavy metals by pH changes.The results indicated that, the spatial variance of Cu, Ni, Fe, Co, Sc and Al in water of the Changjiang River were all very similar. They were mainly associated with the weathering of rocks and minerals. Zn and Pb, Cd and As were also showed a similar distribution, respectively. Natural factors and atmospheric deposition were the sources of Zn and Pb, whereas As and Cd were mainly caused by industrial sewage. The concentrations of Hg presented different profiles, suggesting different origins, and the irregular profiles implied the complexity of pollution sources. Meanwhile, the pollution degree of heavy metals in sediments was Cd>Pb>Cu>As>Zn>Hg, and Cd presented a strong or very strong ecological harm in all sites. The potential ecological risk index of Cu, Zn, Pb, As and Hg were showed minor ecological harm in most sites, while the potential ecological risk index of Cr, Co and Ni were showed minor ecological harm in all sites.The adsorption of soil/sediment to different heavy metal ions was different, therefore, under the same conditons, the migration rate of different types of heavy metal ions in soil was different. Adsorption-desorption, migration and release of heavy metals in soil/sediment were affected by the types of soil/sediment(such as sand or clay soils, etc.), the chemical compositon of soil/sediment solution(such as sepiolite. bentonite, humic acid, etc.), pH, and so on. Sepiolite, bentonite and humic acid enhanced the adsorption of heavy metals in soil, but inhibited their migartion. The release of heavy metals occured mainly in the acidic conditions, and it decreased rapidly with the increase of pH. The chemical compositon of soil solution caused the competitive performance of heavy metal ions in soil, and chemical composition was different, the competitive performance was different. Meanwhile, the speciation of Cd and Pb were all changed when they were absorbed and migrated in soil/sediment, which mostly shifted to acetic acid extration and hydroxylamine hydrochloride extraction, and caused the activity and toxic levels of Cd and Pb to change.