New Method Of Ion-exchange Membrane Electrolysis Kinds Of Sodium Aluminate Solution

Gibbsite crystallization from supersaturated caustic aluminate solution is an important step in bayer process for alumina production form bauxite, which affects the decomposition ratio of supersaturated sodium aluminate solution and the quality of product directly. A new method of ion-exchange membrane electrolysis of caustic aluminate solution was proposed in the present work. The decomposition ratio of supersaturated sodium aluminate solution can be remarkably enhanced with this method which has wide industrial application prospect.The feasibility of the new technique of ion-exchange membrane electrolysis and the decomposition of sodium aluminate solution were identified. In the process of electrolysis, the relationship of electric current with time and the change of particle size was investigated. It was found that temperature,α_k of sodium aluminate solution, solution concentration, the structure of electric tank have great effect on current at constant voltage. The effect of temperature, concentration of caustic aluminate solution, seed coefficient and seed size, time of decomposition on the decomposition ratio of ion-exchange membrane electrolysis and on the size of decomposition product were studied. Conclusions were made as follows:1.Ion-exchange membrane is highly effective and selective to ion with low energy consumption. It can prevent OH~- of cathode chamber from moving back effectively in the process of electrolysis, cause protonation in anode chamber and causticization in cathode chamber, reduce theα_k of sodium aluminate solution in anode chamber effectively. As a result, the decomposition rate of supersaturated sodium aluminate solution can be increased.2.The concentration of sodium aluminate solutions and temperature have great affect on the current in the process of electrolysis. With the sameα_k of sodium aluminate solution, the current is increased as the concentration of sodium aluminate solutions is reduced at constant electric potential. With the same concentration of sodium aluminate solution, the current is elevated as temperature is increased. With the same caustic concentration, the current is increased asα_k of sodium aluminate solution is increased and the interval of poles is reduced.3.The decomposition ratio of sodium aluminate solution can be raised enormously with the techniquie of ion-exchange membrane electrolysis. With the same seed size and seed coefficient, the decomposition ratio is elevated as temperature is reduced (50～80℃). Decomposition ratio of sodium aluminate solution of low and middle concentration is higher than that of sodium aluminate solution of high concentration. The effect of larger seed coefficient and finer seed particles on the decomposition ratio is great at the beginning of the experiments, and the influence is gradually weakened after 3 hours.4.The decomposition product of sodium aluminate solution after ion exchange membranes electrolysis is fine. The size of particles relates to temperature, time of decomposition and concentration of sodium aluminate solution.