Extraction of Heavy Metals from Aqueous Solution

• Main Authors: Szu W. Sung, 宋斯偉
• Other Authors: Sheng H. Lin
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/04759879729724740461

碩士 === 元智大學 === 化學工程研究所 === 87 === The objectives of this study are to utilize extraction method for removal of heavy metals from wastewater. Water/oil/water (W/O/W) emulsion liquid membrane (ELM) and Liquid-liquid-extraction methods were, respectively, employed for extracting Cr6+ and zinc and cadmium ions from aqueous solution. Batch extractions by liquid membrane were conducted to investigate the effects of all operating variables on the Cr6+ removal efficiency so as to enable considered included extraction time, pH, impeller speed of emulsion preparation, baffles and impeller speed during extraction, surfactant and carrier concentrations, sodium hydroxide concentration, temperature and the amount of emulsion relative to the amount of wastewater. Multistage operation of liquid membrane extraction was performed with an aim of improving the overall Cr6+ extraction efficiency. Using the Langmuir and Freundlish isotherm, the Cr6+ removal for the two-stage extraction was experimentally and theoretically invertigated. The test results indicated that the two-stage extraction is a more efficient process that the single-stage operation in terms saving of the amount of extraction emulsion for the same extraction duty. D2EHPA (Di-(2-ethyl-hexyl) phosphoric acid) was observed to be a good extraction agent for zinc removal from wastewater in the liquid-liquid extraction process. Another extraction agent, HEHEHP (2-ethyl-hexyl phosphonic acid mono-2-ethyl-hexyl ester), was seen to be good one for extracting cadmium from wastewater. The McCabe-Thiele method was employed to determine the number of ideal stage of these liquid-liquid extraction processes. Both experimental and theoretical investigations were conducted to compare the efficiency of countercurrent multistage extraction in comparison with the single-stage operation. Finally, the optimum operating conditions were determined for effective heavy metal removal removal by the extraction processes.