Experimental investigation was performed on the removal of chromium (VI) ion from waste water by liquid membrane technology through both batch and continuous operations. The membrane carrier used was tridodecylamine. Extraction mechanism of chromium(VI) ion through the liquid membrane was simulated by mathematical modeling.
For the experiment of membrane stability, the effects of system variables, such as surfactant concentration, stirring speed, concentration of sodium hydroxide, the volume ratio of aqueous and oil phase, and pH of external continuous phase, were analyzed. The most stable formation of liquid membrane emulsion was obtained when surfactant concentration is 3 wt%, and the volume ratio of aqueous and oil phase is 0.5.
A beaker scale experiment was carried out to observe the extraction rate of chromium(VI) ion from waste water under the stable condition. The most important system variable among others were found to be the carrier concentration and the volume ratio of emulsion and waste water.
A two-stage continuous operation can lower the level of chromium(VI) ion concentration in waste water from 1000 ppm to 4.8 ppm by using the emulsion solutions containing 3 wt% of carrier concentration and 0.1 N aqueous solution of sodiumhydroxide with the volume ratio of emulsion and waste water equal to 0.33, and while with the volume ratio of emulsion and waste water equal to 0.2, it can lower the chromium(VI) ion concentration from 1000 ppm to 35.5 ppm.
The capital cost for the two-stage continuous system handling one hundred thousand gallons of chromium(VI) ion waste water per day has been estimated to be about $ 437,200, and can be comparable to $ 539,500 for the conventional reduction-precipitation system.
