| Summary: | 碩士 === 國立臺北科技大學 === 環境工程與管理研究所 === 99 === The purpose of this study is to propose a process combining micellar-enhanced ultrafiltration by CTAB and membrane electrodialysis for the process of spent plating solution to purify, concentrate and recover chromate.
The result showed that CMC of CTAB calculated by conductivity method was 1 mM. The operating pressure of MEUF system was 30 psi, taking chromate rejection and system flux into account. When pH<5, the chromate existed as HCrO4- which caused rejection to increase. Adding enough CTAB in chromate wastewater at any pH value could cause chromate to achieve optimal rejection. In addition, at the same ratio of mole ([CTAB]/[Cr(VI)]) the rejection of chromate increased when feed concentration of chromate was higher. When pH was 3, chromate was 50 mg/L, operating pressure was 30 psi, [CTAB]/[Cr(VI)] was 3 and system volume ratio reached 95 %, the concentration of chromate increased to 26.6 times of raw wastewater concentration in the MEUF system.
The result showed that the recovery efficiency of chromate used anion-exchange membrane (AEM) in membrane electrodialysis system was higher than recovery efficiency of CATB used cation-exchange membrane (CEM). The cost of electricity could be reduced when feed concentration of chromate increased. Thus, this study used MEUF system to concentrate of chromate in wastewater. The result showed that recovery efficiency of chromate increased when current density elevated. However, current efficiency would reduce from reaction of electrolyzed water when current density was higher. When current density was 20 mA/cm2, operating time was 360 min, the recovery efficiency of chromate was 88.2 %.
The spent plating solution of industrial wastewater contained copper, nickel and chromate. Using the MEUF system when operating pressure was 30 psi, [CTAB]/[Cr(VI)] was 1 and system volume ratio reached 95 %, the concentration of chromate, copper and nickel increased to 9.3, 2.3 and 1.1 times of raw wastewater concentration, respectively. And the mass rejection efficiency of chromate, copper and nickel was 71.5 %, 13.6 %, and 6.6 %, respectively. The result could achieve purpose of purification and concentration for chromate. Using the membrane electrodialysis system when current density was 20 mA/cm2, operating time was 360 min, the recovery efficiency of chromate was 85.3 %. The result could achieve purpose of recovery for chromate.
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