A STUDY ON HEAVY METAL SPECIATION IN POLLUTED-RIVER WATER USING A CHEMICAL EQUILIBRIUM MODEL
污染水体重金属形态分布的化学平衡模式

Speciation of cadmium, lead and copper in polluted river water from-Xiawan section of Xiangjiang River was investigated using a modified REDEQL2 chemical equilibrium program. 12 metals and 12 ligands that form 134 complexes, 42 precipitates, 2 mixed solid precipitates, 5 oxidation-reduction reactions and adsorption of the metals on suspended solids -were considered according to water quality data collected during a period of 1982 to 1985. The precipitation diagrams were simulated and the comple-xation capacities, conditional stability constants and adsorption constants were measured so as to derive the model input parameters. The calculated results, which were quite consistent with measured data, indicated that at pH 7.5-8. 0 the dominant species are precipitates and adsorbed forms and the dissolved species, including free ions and inorganic complexes, account, for less than 10% of metals in the system. As pH decreases, the fractions, of dissolved metals increase sharply.