Extraction Of Cr～(6+) From Electroplate Wastewater In An Impinging Extractor

Electroplate wastewater is one of the most dangerous and harmful wastewaters to environment. This thesis reviewed its sources and the current treatment methods. Furthermore, the principle and applications, especially in extraction operation, of impinging stream was summarized. An impinging stream extractor was designed and applied for extracting poisonous Cr6+ from acidic model wastewater which is similar to the electroplate wastewater. TBP, kerosene, and sodium hydroxide were chosen as an extraction agent, dilution agent, and back-extraction agent in this system, respectively.Based on systematic experiments, the proper operation conditions, the ratio of organic phase over water phase (phase ratio) of 1:1 or 2:1, the extraction time of about 1 minute, and pH=1.0 were obtained under the constant TBP volume fraction of 10% in organic phase. The extraction efficiency is around 30% under the aforementioned conditions.The stirring intensity, extraction temperature, the distance between two impinging nozzles, and the fluid flow rate all play significant effect on the performance of the impinging extractor. The optimal operating conditions, stirring intensity of 600 rotation per minute, the extraction temperature of around 30℃, and the ratio of the distance between two nozzles over their same diameter of 3.77～5.9 were obtained under the above extraction conditions in this impinging extractor, and about 40% extraction efficiency was achieved.Compared with traditional stirring extraction equipment, a strengthen mass transfer zone can be achieved by the impinging with counter current injections, and the mass transfer between the extraction agent and the model pollutant can be intensified effectively in the impinging extractor. In single extraction stage, the extraction efficiency of this extractor improves up to 20% over that of the traditional extractor.