The Fundamental Research On Removing Copper From Cobalt Electrolyte And Nickel Electrolyte By Ion-exchange With Novel Silica-polyamine Organic-inorganic Composite Resin

The removal of copper from cobalt and nickel electrolyte is a vital step in the processes of cobalt and nickel electrorefining. In view of the disadvantages of traditional methods, a new and environment-friendly technology of removing copper from cobalt electrolyte and nickel electrolyte by ion-exchange process is put forward. Based on the optimum selection of resins, a novel silica-polyamine based composite chelating resin CuWRAM with a function group of aminomethyl pyridine was used for the first time to investigate the removal of copper from electrolyte systems of cobalt and nickel. The research systems include sulfate, chloride and sulfate-chloride mixed systems. It is very promising to solve the existing problems of removing copper from cobalt and nickel electrolyte, and result in no residue in the processes of removing copper. The researches include characterizations of resin, research of technology and application, and mechanism.Compared to those of the anion and cation resins which can only be used single system, CuWRAM chelating resin can be widely used in multi-system, such as sulfate, chloride and sulfate-chloride mixed systems. The advantages of this resin include simplicity in device, ease of operation and high separation efficiency. In the processes of removing copper from the electrolyte of cobalt and nickel, the adsorption of copper was affected by pH, temperature and contact time, but not be influenced by copper concentration. The optimum operation condition were pH=4, contact time of 30 min and ambient temperature. The loaded resin can be eluted efficiently by 2.0mol/LH2SO4 at a contact time of 40 min. Saturation adsorption is more favorable than breakthrough adsorption, and a purer copper sulphate enriched solution can be obtained. Compared to those of organic resins for adsorption copper including D850,D860,D463 and D751, CuWRAM resin exhibited much better performance in separation of copper from nickel and cobalt, especially in cobalt electrolyte. CuWRAM is applicable to the removal of copper from the industrial electrolyte of nickel and cobalt, which suggest the prospective future of this resin. Thermodynamic equilibrium studies showed both the Langmir and Freundich isotherm equation fitted the experimental data well. The R-square values were all greater than 0.97 at different temperatures. PositiveΔH indicated that the process of adsorption copper is endothermic, and increasing temperature benefit resin's adsorption. NegativeΔG show that the processes of adsorption copper carry out spontaneously; AS value increased in the process of adsorption of copper, which showed the resin had preferential adsorption toward copper.The kinetics processes of copper being adsorbed onto CuWRAM from cobalt electrolyte and nickel electrolyte were investigated. According to shrinking core model, adsorption processes are controlled by both the particle diffusion and chemical reaction. The rate constant increased with the increase of temperature, which implied accelerated the adsorption rate at higher temperature. The pseudo-second-order model fitted the experimental data very well than the pseudo-first-order. These indicated the reaction of copper adsorbed onto CuWRAM approximate to the pseudo-second-order kinetic reaction.The study about micro-mechanism showed there are two steps in the process of adsorption copper for CuWRAM. At first, the resin was protonated, followed by the adsorption of copper to aminomethyl pyridine functional group of CuWRAM; at the same time, the hydrogen ion on resin were exchanged, which resulted in the decrease of copper exchange capacity with the decrease of solution pH. The result of IR spectrum analysis disclosed that the coordination between N atom of the resin and Cu(Ⅱ) was the main reaction in the processes of copper adsorption. In the sulphate system, N atom coordinated with the hydration copper ion. In the chloride system, N atom coordinated with the complex of copper and chloride. In the mixing system of sulphate and chloride, both coordinations are thought to happen. The distribution of copper for CuWRAM resin increased with the increase of Cl- concentration in feed solution but almost not change with SO42- concentration. The formation of complexing anion between Cu2+and Cl- decreased the repulsion by the function group containing positive charge of resin under acidic condition, which resulted in the increase of copper distribution in chloride system. It was found that the second ionization energy of copper and the replacement velocity constant of complexing water in copper ion were larger than those of cobalt and nickel, resulting in preferential selection of copper in the electrolyte of nickel and cobalt.