Several Key Scientific Problems Researches On Diffusion Dialysis

Diffusion dialysis(DD) becomes one of the most promising separation techniques due to low energy consumption, no environmental pollution, easy operation and etc. Thus, the production industries, including steel production, metal refining, electroplating, non-ferrous metal refining and etc., start to focus on DD technique with increasing serious environmental pollution and resources shortage.In practical DD application, there is always a harsh operation condition, such as high temperature, high acid or alkali, heavy metal salts content, strong oxidization or organic solvents. So, the membrane materials with high physic-chemical stability and separation effect are strongly required. Accordingly, the membranes that can be used in DD processes are quite limited. Besides, in the metal production industries, different kinds of strong acids will be selected according to different application backgrounds. Thus, large quantities of different acidic wastes with all kinds of metal salts will be produced. If DD is employed to treat those wastes, the different acids and metal salts will affect DD performance significantly. In order to investigate and deal with the above scientific problems, organic-inorganic hybride ion exchange membranes for DD are designed. Then, high temperature DD performances for hybrid membranes are investigated in HCl+FeCl2solution. And the effects of different acids and metal salts on hybrid membranes DD are also discussed based on mathematical model. The main contents can be summarized as followings:(1) Poly(2,6-dimethyl-1,4-phenylene oxide)(PPO)-SiO2hybrid membranes, which are produced from hydroxylation with KOH, quatemization with Trimethyl-amine(TMA), sol-gel reaction with TEOS of brominated PPO, have been prepared. Among them, TMA is used to bring in strong ion exchange groups to assure IEC and WR; inorganic silica TEOS is to combine the merits of organic and inorganic materials, endowing excellent physic-chemical stabilities and mechanical stability to membranes. From the membranes characterizations, it’s demonstrated that the hybrid membranes’ stabilities have been enhanced obviously, and high IEC and proper Wr can be obtained.(2) High temperature DD for hybrid membranes has been tested, and the temperatures are ranged from15℃to65℃. Research on high temperature DD process is meaningful:first, the wastes discharged from factories are in high temperature due to continuous processing and friction forces; second, high temperature is advantageous to ion transport. With increasing temperatures, excellent DD performances can be obtained, and separation factor(S) can be as high as41, while commercial membrane DF-120shows low separation effect throughout. The excellent DD results, especially at high temperature, can be ascribed to the silica network formation.(3) The effect of different acids on DD effects are discussed based on a mathematical model. The following systems are selected:HCl+NaCl, H2SO4+Na2SO4, and H3PO4+Na3PO4. Due to intensive stirring, the effects of liquid films can be neglected and the preudo-steady state of DD process is supposed for simplification. Then, the basic differential equations describing the dependence of the total anion concentrations upon time can be obtained, combined with the optimized procedure. The optimized dialysis coefficient P can be further fitted based on the experimental ions concentrations at different times. And P is used to describe the acid effect on DD quantitively. The final fitted results are as following:PH2SO4total(2.50×10-6m/s)>PHCl (1.60×10-6m/s)>PH3PO4total(1.0×10-7m/s). After correlation Cl-, SO42-and PO43-charicters with P trends, it’s found ions adsorption and diffusivity in membrane and the ions initial concentrations in waste are the important factors to affect DD performance. This model is simple and easy to use, so it is readily available for users, including those who don’t engate in DD.(4) Then, the model is modified and expanded to investigate the effects of different metal salts on DD. The investigated systems are HCl+NaCl, HCl+FeCl2, HCl+NiCl2, HCl+CuCl2, HCl+ZnCl2and HCI+AICl3. The fitted results are PCl-(CuCl2)(6.1×10-6m/s)> PCl-(FeCl2)(3.1×10-6m/s)>PXCl-(NiCl2)(2.6×10-6m/s)>PCl-(NaCl-)(2.0×10-6m/s)>PCl-(NaCl-)(1.6×10-6m/s)>PCl-(ZnCl2)(3.4×10-7m/s). The metal ions effects on HC1DD are mainly resulted from the complexes formation between metal ions and Cl-. In summary, Pci-is highly related with metal ions charicters, and the charge, volume, stability coefficients of complexes.