The Modification Of Ion-exchange Membrane And The Applications In Cobalt Electrodeposition

With the progress of science and technology of human society, the demand for cobalt is growing in people daily life and production. Cobalt is widely used in the production of high hardness and wear-resistant alloys, high temperature alloys, pigment, battertis and medical and other fields, so an efficient environmental protection and economic efficiency of pure cobalt preparation method is urgently needed in industrial production. In the traditional cobalt electrodeposition progress, it will produce chlorine at the andoe, which will damage the environment and health of workers, while the hydrogen evolution reaction will occur at the cathode, which will reduce the current efficiency.Ion-exchange membrane is a function of the separation membrane, which has a specific selectivity for specific ions, also has good conductivity, high stability and belongs to a planar structure. So Ion-exchange membrane is well suited for the production of cobalt electrodeposition.In this work, the improvements were studied that the ion exchange membrane was applied in the traditional cobalt electrodeposition process to prevent chlorine gas from generating at the anode and the hydrogen evolution from generating at the cathode.First, the performances of the ion exchange membranes tested were measured about its thickness, degree of swelling, water content, ion exchange capacity, the ion permeability properties, membrane resistance and membrane potentials. The comparative analysis of these properties were researched to select the appropriate method for modifying.The modified method for ion exchange membrane is ultraviolet radiation grafting Sulfobetaines(SBMA), the best modification conditions through a series of single factor experiments were as follows: SBMA monomer using methanol as solvent, exposure time was 120 s, SBMA monomer concentration was the cation exchange membrane was 60 g / L, the anion exchange membrane was 80 g / L, exposure intensity: the cation exchange membrane: 12 m W / cm2, the anion exchange membrane was 10 m W / cm2. The contact angle after modified of cation exchange membrane and anion exchange membrane decreased by 23° and 20° respectively. The results indicated the increase of hydrophilictiy and the decrease of membrane resistance after the improvement. The water content and degree of swelling of the two ion-exchange membrane after modification were increase, which is due to graft hydrophilic group SBMA moisture. Ion-exchange capacity is increased, indicating graft SBMA is successful. Anion exchange membrane barrier to improve the hydrogen ions, the cation exchange membrane barrier to improve the chloride ions. Membrane resistance decreases, and both ion exchange membrane in different solutions’ s over potential were decline, and remain stable.The two kinds of the modified ion exchange membrane were applied to cobalt electrodeposition process, the optimum conditions were: temperature 50℃, current density of 250 A/m2, Co concentration of 30 g/L, stirring speed of 400 rpm. under optimized conditions, the current efficiency was 98.93% and energy consumption 35.41 k Wh/t when electrodeposition 2 h. Under optimum conditions, use the modified ion exchange membrane to electrodepsite cobalt, the current efficiency increased from 98.93% to 99.17%, energy consumption decreased from 35.41 k Wh/tto 33.25 k Wh/t.A model of ion transfer across ion-exchange membrane was set up and was analyzed with cyclic voltammetry method(CV). The conclusion is the positive and negative ends of potential windows were determined by the cation and anion which transmitted to the ion-exchange membrane respectively. And the harder cation transmitted through ion-exchange membrane, the positive end of potential window shifted to the positive side, the harder anion transmitte throgh ion-exchange membrane, the negative end of potential window shifted to the negative side.