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Adsorption of Cadmium Onto Sediments of Hydro-Fluctuation Belt in Three Goerge Reservoir and Its Potential Influence on Water Pollution

Author: PuPeng
Tutor: FuWaLi
School: Southwestern University
Course: Physical Geography
Keywords: Three Gorges Reservoir with sediment Heavy metal pollution Cadmium adsorption Particle effects Metastable equilibrium theory
CLC: P595
Type: Master's thesis
Year: 2011
Downloads: 61
Quote: 0
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Abstract


Three Gorges Reservoir with a multi-complex system, it is in a transitional connection zone between land and water, water, land two regional structure, function and unique environmental landscape characteristics. However, due to natural and man-made causes, Gorges Reservoir ecosystem showing strong ecological vulnerability and instability. The drawdown band due to its characteristics of the cyclical fluctuations of the water level, makes fluctuating zone sediments at the same time its different - in the flood period, the occurrence of sedimentary belt in the drawdown of the general characteristics of the riverbed sediments can also be considered as part of the riverbed deposition; fall dry, due to human disturbance, and other exogenous substances enter, coupled with the seasonal changes of the water level of seasonal changes on the water level in the reservoir with natural riverbed opposite, making the fluctuating zone deposition the nature of the material, especially for heavy metal suction held performance may differ from the traditional sense of the riverbed sediments. Drawdown with the pH of the soil as well as Cu, Zn, Pb, Cr, Cd, Ni content of heavy metals and their spatial distribution characteristics based on analysis of a small river basin in the investigation, the simulation analysis of the fluctuating zone sediments of the heavy metals cadmium ion The adsorption characteristics. The results are as follows: the average content of heavy metals in soil in the study area: Cd 0.387mg/kg; the of Cr 57.196mg/kg; of Cu 28.685mg/kg; of Ni 27.910 mg / kg; Pd 35.567 mg / kg; the Zn 126.028 mg / kg. The use of single-factor analysis of Cd, Cr, Cu, Ni, Pb, Zn average pollution index of six heavy metal elements to evaluate the soil samples Cd, Zn, Pb pollution index were 1.935,1.26 and 1.016 Cu, Cr, Ni state of clean, pollution index 0.82,0.636,0.698 of cadmium adsorption simulation analysis shows that: the Three Gorges Reservoir is closely related with the sediment on the adsorption of heavy metals and sediment particle size, adsorption intensity and adsorption rate with the particle size decreases, cadmium ion adsorption kinetics experiments showed that the adsorption process has gone through three phases of rapid growth, the gradient and dynamic balance, adsorption kinetic characteristics in line with the Lagergren pseudo-first order kinetic equation. Quasi-second-order equation does not apply. By studying the temperature fluctuating zone sediments Absorbation found that the adsorption process is an endothermic reaction, adsorption kinetics curves increase with temperature rise, under the experimental conditions, the adsorption process includes both molecular adsorption, and ion exchange adsorption, and ion exchange adsorption mainly. Thermodynamic parameters showed that the the fluctuating zone sediments cadmium ion adsorption process is a spontaneous endothermic reaction, and as the temperature rises, the greater the degrees of freedom of the cadmium ions in the solid - liquid interface. This indicates that winter flooded conditions, the low temperature of the water body environment conducive to the desorption process of cadmium ions between the sediment and water body, makes cadmium ions adsorbed on sediment and re-enter the water column, with the water migration thus become a secondary source of pollution. The results showed that the adsorption isotherms were fitted fluctuating zone sediments of cadmium ion adsorption isotherms Langmuir and Freundlich models at the same time, a higher coefficient of determination and Freundlich models, indicating that the latter is more able to accurately describe the sediments on cadmium ion response adsorption isotherm. The model parameters that fluctuating zone sediments are strong suction holders of cadmium ions. By changing the initial concentration of the sediment was found in the case of temperature, pH and other conditions are the same, fluctuating zone sediments showing particle effects (solid concentration effect) on the adsorption of cadmium ions. The adsorption density decreases with the increase of the initial concentration of the sediments. Can be supplemented by the metastable equilibrium theory, theory semi-empirical quantitative explanation of this phenomenon.

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