Investigation Of The Mechanisms Of The Heavy Metal Speciation And Removal As A Function Of PH Via Micellar Enhanced Ultrafiltration

Micellar-enhanced ultrafiltration（MEUF） is a new treatment process developed recently to remove heavy metals and organic pollutant from wastewater, which combines ultrafiltration with surfactant technology. Compared with the traditional ultrafiltration technology, micellar-enhanced ultrafiltration has several preponderances in removing heavy metal ions, such as high separation efficiency, low energy requirement, low cost and simple operation, etc. MEUF is a complex process and removal efficiency depends on many parameters, for instance the concentration and characteristic of surfactants, the concentration of pollutant, solution pH and applied pressure, etc. In which, pH has a certain influence on membrane, surfactant and heavy metal ions speciation and so on. Metal ions speciation affects the migration, transformation and biological availability. Meanwhile, the causes of various forms of heavy metals and their biological and chemical processes are involved in, there are differences. It is different from adsorption ability between various metal ions speciation and surfactants, thus the removal efficiency of ultrafiltration experiments will vary greatly. Therefore, it is extremely significant for research in the form of heavy metals in environmental assessment and exploration of the heavy metal migration transformation rule.In this paper, the influence of pH on heavy metal speciation and removal from wastewater by MEUF were investigated, using an anionic surfactant（Sodium Dodecyl Sulfate, SDS） and a hydrophilic membrane（Polyether sulfone, PES）. The results of the study are shown as below. The removal of copper and cadmium was more efficient at high pH values（pH>3） with SDS feed concentration of 8 mM and metal ions concentration of 50 mg/L. The rejection of metal ions maintain above 90%. However, in the case of zinc and lead, at high pH values, the precipitation begins to dissolve as hydroxyl complex, therefore the optimal removal efficiency achieved at the pH values within the range of 3-10. Influence of metal concentrations on the metal removal efficiency in the various pH values has also been investigated. From the several studies, it can be seen that, in the case of copper and zinc, the metal ions have high removal efficiency when concentration is below 150 mg/L. Whereas, in the case of cadmium and lead, as the molar mass of the metal ions is high, with the SDS concentration of 8 mM, the optimal concentration can reach 300 mg/L. As a consequence, in the treatment of heavy metal using MEUF, the removal efficiency Rt of metal ions accord with following ranking: Pb²⁺ > Cd²⁺ > Zn²⁺ > Cu²⁺.These results showed that pH is a key parameter in metal ions speciation and removal of metal ions during MEUF, which laid a solid foundation for the application of MEUF in real water treatment, and provides the theoretical foundation for removal of heavy metal wastewater under different pH values.