Studyon Modification Of Cation Exchange Membrane Used In The Process Of Cobalt Electrowinning

The three-compartment double-membrane equipment is composed of anion and cationexchange membrane and electrode.the equipment is used to solve the problem that chlorine ispreparated in the process of traditional cobalt electrowinning, and improve the quality ofcobalt plate.Usually,the heavy metal wastewater is treated by electrolysis,then the waterconforms with the regulations,and the cobalt can be recoverd also.But for the heavy metalwastewater that containing chloride,when is is treated by electrolysis, chlorine is preparated.Chlorine is a pollutant,and can reduce the quality of cobalt plate. The three-compartmentdouble-membrane equipment can be used to solve these problems.Both in thethree-compartment double-membrane equipment for Cobalt electrolysis and in thethree-compartment double-membrane equipment for heavy wastewater treatment,the cationexchange membrane requires a high rate of anion barrier.And because solution in the middlecompartment and anode chamber is acidic,the cation exchange membrane is also required togood resistance to acidic. In research for ion exchange membrane,our country lag far behindother countries especially the development countries,for example American, Japan andGermany. because of technical monopoly,the imported ion-exchange membranes areexpensive,which not only increases the costs for production,but also hinderes thedevelopment of domestic ion exchange membrane.The paper is devoted to modify cationexchange membrane,in order to improve its performance of resistance to acidic and barrier tochloride.then the membrane can be well used in the three-compartment double-membraneequipment to treat the heavy wastewater or preparate cobalt.Also,we want provide some ideasfor the preparation of ion exchange membrane,and provide support for the development ofChina’s membrane industry.We can mainly use surface modification and blending modification to modifycation-exchange membrane. The techniques for surface modification containelectrodeposition,ray radiation, organic solvents coated and particle bombardment.In blendingmodification,we can cast the modifying additive in the casting solution directly,or immersethe ion exchange membrane in modifying solution,then these additives react with the basefilm.The blending modification is usually used to prepare hybrid ion exchange membrane ormodify ion exchange membrane to improve the mechanical and anti-corrosion properties.Currently the additives used for modification maily are inorganic nanoparticles which arehydrophilic,and have large surface area.The membranes which are modified by blendingmodification have incomparable advantages of organic membranes and inorganicmembranes.According to the principles of preparation and modification of ion exchangemembranes, blending modification for membrane is used in this paper.Two kinds of cation exchange membranes, Nafion117and IONSEP-HC,are used for themodification. Tetraethylorthosilicate and zirconium propoxide (IV) are used as the precursor for silica and zirconia.Control the degree of expansion of the membrane by adjusting thepurity of ethanol and the time which the membrane immersed in ethanol. Control theabsorption of the solution of the modified membrane by adjusting the time which themembrane immersed in modification solution. Control the size of the particles of silica andzirconium dioxide by adjusting the water contention of membrane. Then the optimummodification conditions are determined.The leak rate of chloride ion under the experimentalconditions are reduced by53.8%and32.4%for silica-modified Nafion117and IONSEP-HCmembranes respectively. The leak rate of chloride ion under the experimental conditions arereduced by45.4%and24.8%for zirconia-modified Nafion117and IONSEP-HC membranesrespectively.The mechanical properties of the membrane is improved when the inorganicmaterial is Introduced,and the acid resistance of the membrane is improved when the strongacid exchange group is Introduced.Neither Nafion117nor IONSEP–HC can be used in Thethree-compartment double-membrane equipment,because they can not be used under acidicconditions for long time.The modified membrane can effectively reduce the leakage rate ofchloride ions, and reduce the concentration of chlorine in the air. Silica-modified IONSEP-HCmembrane is more suitable for three-compartment double-membrane equipment.