Research On Ion-exchange Membrane Selective Permeability And Its Particles Doping Modification

The method of traditional non-ferrous metal smelting is electrolysing its chloride solutions, although in this method can acquire higher purity metal by replacing the cothode metals this also can cause some serious problems such as producing large amounts of chlorine which not only pollute the environment but also endanger the operator’s health. The process of double membrane and three rooms points at the disadvantage of traditional metal smelting process which produces large amounts of chlorine, this process introducing the anion and cation ion-exchange membranes that divided the traditional electrobath into three compartments, adding the diluted sulfuric acid, the mental chloride solution, the diluted hydrochloric acid into the anode room, the cathode room and the middle room respectively,using the selective permeability of the ion-exchange membrane can not only eliminating the chlorine by the electrolysing process but also can recover the high concentration of hydrochloric acid which can get an extra economic benefits.Some experiments are done in this paper to explore the mechanism of ion-exchange membrane’s selective permeability and propose an imagine that the ζ potential influences the membrane’s elective permeability. Through the experiment: in the same concentrations of different solutions, the higher ion valence the lower cation membrane’s surface ζ potential,while valence is alike, the smaller ion hydrated radius has the higher potential, the chloride ion leakage rate and the concentration of the solution are opposite to the ζ potential changes,the potential reduces firstly and then increases while the pH increases, the same theory adapted to anion membrane. Proposing the ζ potential in the membrane thoroughfare which producing the “source” together with the surface ζ potential that influence the selective permeability of ion-exchange membrane.The PVDF-styrene basement membrane is prepared which the PVDF particle accounts for 14.0%, through testing the membrane’s grafting degree can get the optimum condition of the alkali treat and the reaction of grafting under the protection of nitrogen: the concentration of the KOH ethyl alcohol solution is 0.01mol/L, the alkali treat temperature is 70℃, the reaction time is 50 min, the concentration of homogeneous catalyst（Tetrabutyl ammonium bromide） is 3mg/ml, the reaction time of grafting is 3h, the temperature of grafting is 70℃and the concentration of initiator（Benzoyl peroxide）is 0.4g/100 ml. Under this condition the basement membrane’s grafting degree is 20% more or less. Through testing the sulfonation degree get the best condition of grafted membrane in the 98% oil of vitriol: the sulfonation temperature is 60℃, the sulfonation reaction time is 4h, then the sulfonation degree of the grafted membrane can surpass 1.28mmol/g.The self-made cation ion-exchange membrane has some relatively large aperture by theelectron microscope scans, using the inorgnic nano-particles SiO₂ and Al₂O₃ to modify the self-made cation ion-exchange membrane, through the contrast experiment by using different dosage of the two nano-particles can get some conclusions: the former is better than the latter in modification, when the content of SiO₂ accounts for 0.50% of PVDF, the parameters of the membrane at a relatively high level: the grafting rate is 16.92%, the sulfontion degree is1.28mmol/g, the ion exchange capacity is 1.64mmol/g, the membrane potential is 14.72 mv,the chlorine leakage rate is 4.56%. Then do the double membrane and three rooms smelting experiment by using the self-made membrane and the IONSEO-HC-C membrane, after smelting 4h, in the aspect of t the gradient of chlorine leakage rate the former is 24.56% lower than the latter, so the doped SiO₂ nano-particle modification PVDF-styrene membrane has a better selective permeability than the IONSEO-HC-C membrane.