| In recent decades,with the growth of Chinese national economy,the nonferrous metal smelting industry developed rapidly and played an important role in the development of Chinese national economy.As China attaches great importance to green development,the industry currently has a series of problems such as large energy consumption,excessive discharge of pollutants,and low resource recycling,which restricts the development of the industry.Particularly,there is serious chlorine pollution in the conventional metal chloridization process,which will seriously endanger the health of the body and the surrounding environment.Normally chlorine is treated by lye to absorb it,the absorption of waste water also causes secondary pollution.The application of this membrane combined with electrochemical technology in the dual-membrane three-chamber metallurgical system can solve the problem of chlorine pollution at the source,achieve the goal that is deep separation and acid-base recovery,so this technology has environmental significance and economic value.Ion exchange membranes are the core components of the system,and there is a big gap between the preparation level of ion exchange membranes in China and foreign countries,the membrane product types are single,and the ion exchange membranes on the market are mostly heterophasic membranes.Currently,the homogeneous membranes with excellent performance are mostly in the laboratory stage,and large-scale use mainly depends on imports,and the double-membrane three-compartment membrane metallurgical system solutions are complex and require stringent membrane performance,membranes not only have to meet the conventional performance of ion-exchange membranes,but also need to have higher selectivity for ion permeability,lower membrane resistance and superior stability.At present,this technology is limited because the ion exchange membrane on the market cannot meet the requirements of the double-membrane three-room membrane metallurgy system.Therefore,the development of an ion exchange membrane which is suitable for the double-membrane three-compartment membrane metallurgy system plays a key role in the development of membrane metallurgy technology.The content of this study was based on the semi-interpenetrating network structure,in order to improve the defect of the traditional out-of-phase film bonding structure,added the PVDF polymer organic polymer through solution blending method,then use concentrated sulfuric acid as the sulfonation agent to perform sulfonation on the intramolecular exchange group,and finally adopted hot press method to prepare a PVDF/semi-interpenetrating network structure ion exchange membrane.According to the specific requirements of the double-membrane three-room membrane metallurgy,the membrane performance indicators and test methods were determined,in order to determine the best membrane preparation conditions,the sulfonation reaction process and the effects of the dosage of crosslinker like DVB and PVDF on the film formation performance were explored.Finally,by simulating the operation of the pellicle in the double-membrane three-compartment metallurgy system,the performance of the three cation membranes was compared.Studies showed that a more semi-interpenetrating network structure can be constructed by solution blending and active groups can be successfully added by sulfonation with concentrated sulfuric acid through SEM scanning electron microscopy and FTIR Fourier transform infrared spectroscopy analysis.The addition of a catalyst and a swelling agent during the sulfonation reaction can effectively increase the sulfonation efficiency.The best sulfonation effect can be obtained when the sulfonation time was 8 h and the sulfonation temperature was controlled at 80°C.The relationship between the performance indicators of ion exchange membranes was relatively close.The degree of cross-linking and density of the network structure is affected by the amount of DVB dose,IEC will gradually increase with the increase of DVB dosage,IEC reached the maximum when the amount of DVB is 2 m L,and the effect of intra-membrane potential was enhanced,the chloride ion leakage rate was effectively controlled after the amount of DVB is higher than 2m L.The increase in the degree of cross-linking maked the intra-membrane structure more compact and stable,and increased the burst strength of the film,but it also hinder the access of sulfonic acid groups and increase the membrane resistance.The membrane IEC became largest when the PVDF dosage is about 20 g.The blocking effect on chloride ions was enhanced when the degree of dense structure inside the membrane and the potential increased.If the content of PVDF in the membrane was too high,the electric field density of the membrane exchange group would be reduced,and the electrical repulsive force of the functional group to chloride ions was reduced,the leakage rate of chloride ion became larger when the dose of PVDF exceeds 20 g.The PVDF plays a certain supporting role,the more amount of PVDF added,the higher strength of the prepared PVDF/semi-interpenetrating network structure ion exchange membrane.PVDF is an inert hydrophobic non-conductive material,the inert membrane skeleton can block the conduction of ions and result in the increase in the membrane resistance,the membrane resistance increased faster when the dosage of PVDF exceed 20 g.In summary,taked into account the mutual influence of the membrane performance indicators,then determined the sulfonation reaction time of 8h,sulfonation temperature of 80 °C,DVB dosage of 2m L,PVDF dosage of 20 g was the best preparation conditions.The optimum dosage of styrene,DVB and PVDF proportion is 10:1:10.The prepared PVDF/semi-interpenetrating network structure ion exchange membrane can be used under normal conditions,under the condition without net cloth,the bursting resistance reached 0.57 MPa,the moisture content was 29.7%,and the membrane resistance was controlled at 5.57 ?·cm2,the number of migrations reached 95.3%,except the rupture strength,the above indexes were superior to the traditional hetero-phase membranes.The performance of the obtained membrane during application showed that the chloride ion leakage rate of the prepared PVDF/semi-interpenetrating network membrane was significantly lower than that of the commercial membrane,slightly higher than that of the homogeneous membrane,and the chloride ion leakage rate was 4.21% after 4 hours electrolysis.During the entire operation of the membrane,the membrane surface resistance kept substantially constant,which was smaller than that of the conventional heterogeneous membrane and slightly higher than that of the inlet homogeneous membrane when the operating current was increased.The effect of long-term electric driving caused the exchange groups in the ion exchange membrane was sheded,and the PVDF/semi-interpenetrating network structural membrane can be stably operated under high current density conditions for more than 20 days,the exchange capacity would has a tendency to decline when the temperature was higher than 60°C,and it can meet the application needs.The membrane preparation method of this study combines the preparation of homogeneous membranes and heterogeneous membranes,and the process is relatively complicated,but the industrial level of our country and the preparation of heterophase membranes have industrial advantages.In the future,the leakage of chloride ions will continue to be reduced,through the membrane modification study,then zero pollution will be realized in the double-membrane three-compartment membrane metallurgy system,and different macromolecular polymers may be selected for different separation requirements,so that the membranes have different separations performance,and the use of membranes will be expanded,the green development of the non-ferrous metals industry can also be promoted. |
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