Mechanism And Application Research Of The Permeate In Micellar-enhanced Ultrafiltration By Using Foam Fractionation

This study focuses on mechanisms and application of the permeate in Micellar-Enhanced Ultrafiltration (MEUF) by using Foam Fractionation (FF). Sodium Dodecyl Sulfate (SDS) was applied as the surfactant. Effects of operation parameters on foam fractionation process were investigated systemically. The conditions of separation process were optimized. The selectivity of the foam fractionation of mixture ions was investigated. The effect of combined technique on separations was studied. In addition, mechanisms of foam fractionation were analyzed by surface chemistry nature and foam performance of SDS, dynamics process of foam fractionation and distribution of air bubble size.Firstly, the present situation and harm of heavy metal pollution were summarized, the application prospect and existence question of the technique of MEUF and FF in the environmental protection were introduced, and the purpose and content of the research were also proposed. Next, the surface chemistry nature, the micelle characteristic and foam performance of SDS were investigated. The Critical Micelle Concentration (CMC) of SDS is 7.8×10-3mol/L in the pure water at 25℃. The area Am of SDS was 0.46nm2, and the surfactant was exactly erect in the foam surface. The saturated adsorptive capacityΓm is 3.6×10-10mol/cm2 by using Langmuir adsorption equation. The temperature, the pH value, and the concentration of heavy metal ions and NaCl, had the obvious influence on CMC. The process of SDS micelles was the entropy-driven process which was carried on spontaneously. The SDS concentration, the pH value, the temperature, the ethanol concentration, the NaCl concentration, and the concentration of heavy metal ions, had the influence on the foam performance of SDS markedly. The transformation rule of vibrate and ventilate to estimate foam performance of SDS was consistent basically. The effects of conditions of air flow rate, SDS concentration, and ionic strength on air bubble characteristic of separation equipment were investigated. The size and distribution of air bubble were studied by using image recognition software IPP6.0. The direct influencing factor of air bubble diameter was the aperture size of separation equipment, and the operating parameters of foam fractionation were also influential. The mean diameter of air bubble was below 2mm under the experimental condition. By using foam fractionation to treat the permeate in MEUF, the Cd2+ concentration in the effluent was lower than 0.1 mg/L which could meet the integrated wastewater discharge standard (the first grade of national discharge standards in China). The Cd2+ dynamics research of foam fractionation conformed to the first-order kinetic equation. The air flow rate, the temperature, the pH value, and the concentration of SDS had the obvious influence on separation rate constant k. We use foam fractionation to treat wastewater containing mixed metal ions. Results showed that the SDS had the good selectivity to three metal ions. Finally, the study was to adopt the combined technique of MEUF-FF to treat the wastewater. Compared with the single MEUF, the combined technique of MEUF-FF could reduce the amount of SDS consumption significantly. After using combined technique it enhanced the separation efficiency of heavy metal ions markedly and decreased the concentration of SDS in the effluent.The method of image analysis was applied to review the size and distribution of air bubble in the paper. To study the dynamics process of foam fractionation and the selectivity of the mixture of metal ions, mechanism of foam fractionation process was primarily discussed. Effects of operation parameters on foam fractionation process and optimization of craft were investigated simultaneously. The result indicated that the Cd2+ concentration in the effluent could meet the integrated wastewater discharge standard by using foam fractionation to treat the permeate in MEUF. The combined technique of MEUF-FF could enhance the separation efficiency of metal ions markedly and decrease the concentration of SDS in the effluent. The study provides value for application and the broad prospects for heavy metal-containing wastewater treatment by combined technique of MEUF-FF.