Use of Electrodialysis to Remove Heavy Metals from Water

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Abstract
The removal of heavy metals from water by using electrodialysis is discussed. Parameters studied include current efficiency, stack resistance, and osmotic water transfer. Four single-electrolyte systems are investigated: CdCl2 and CdSO4 are used as representative heavy metal salts; NaCl and CaCl2 are studied in order to enhance the understanding of physical electrodialytic processes in general and to provide a basis of comparison. The variables of electrolyte type, electrolyte concentration, pH, temperature, and elapsed time of membrane usage are examined. Results indicate that the purification of cadmium-laden waters can be achieved while maintaining high current efficiencies and reasonable stack resistances. The osmotic water transfers (in units of liter/mole) of the above cadmium salts are small enough to allow a high percentage of a wastewater stream to be reclaimed as purified water. but are higher than the water transfers of NaCl and CaCl2 due to increased hydration effects.