| Summary: | 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.
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