关键词: 泥沙, 解吸, 重金属, 动力学模式

Abstract: Heavy-metal pollutants entering into natural rivers can be adsorbed by suspended solids in water. and will be mainly adsorbed by sediment particles. This is a major way by which heavy-metal pollutants change into a solid phase from an unsaturated liquid phase. and the water takes place selfpurification. On the other hand, sediment particles adsoring heavy-metal pollutants, namely, sediment particles comtaminated by heavy-metal pollutants may release heavy-metal pollutants to make the water polluted secondarily under certain apuatic environment conditions. For example. sediment contaminated by heavy-metals enters a "clean" water, or bed mud polluted by heavy-metals turns into a suspended load (Aquatic environmental chemistry conditions also take place changes.). For another example. while dredging in revers. sediment on bed will be disturbed to suspend upwords. It is founded frequently that heavy-metal pollutant concentration in water phase increases a lot during the dredging. This phenomenon was studied by several pioneers through changing artificially environmental, chemical conditions in reactions. For example, acid is added to change the value of PH or a great quantiy of other metalions are added to change total ionic concentration of the aqueous solution to observe the variation of heavy-meal concentration in water phase . Grain size of sediments in natural rivers is non-uniform, and adsorption-desorption capacities of the sediments with different grain sizes are quite different. Laboratorial experiments of desorption by sediments with different grain sizes are conducted in the paoer by modelling sediment contaminated by Cd. Kinetics characteristics of desorption by sediments with different grain sizes (in the light of uniform sediment) is studied and discussed at first, and then kinetics model of desorption by sediments with different grain sizes is studied and discussed- Main conclusions are as follows.(l) Combining the adsorption reaction Kinetics equation with the mass conservation equation,formulae used to calculate residual adsorption content of specific weight sediment and heavy-metal pollutant concentration in water phase are deduced in the case of desorption by sediment. Experimental data agree with them fairly well. Furthermore, formulae for calculating equilibrium residual adsorption content of specific weight sediment and equilibrium heavy-metal pollutant concentration in water phase are also obtained. These can be treated as the basis for further quantitaively studying characteristics of desorption by sediments.(2) Generally speaking, coarse sediment particles have weak adsorption abilities and strong desorption abilities, So in the study of the release of heavy-metal pollutants by sediments in rivers,great attention should be paid to the coarse sediment particles with high content of heavy-metal pollutants. Moreover, the higher the sediment concentration, the higher the concentration of heavy-metal pollutants in water phase. Therefore, When dredging sediments polluted by heavy-metal pollutants, attention must ha paid to the control of the sediment concentration during the operation.(3) Concurrent desorption kinetics model by sediments with different grain sizes is Eq. (4-4).It indicates that there is no competition or interference among different grain sizes its residual adsorption content of specific weight of sediments is the sum of the residual adsorption contents of each grain size.

Key words: sediment, desorption, heavy-metal pollutant, Grain size