| With the rapid development of China’s aluminum industry,the grade of bauxite has been declining year by year,and the efficient utilization of low-grade bauxite rich in various impurities has become an urgent problem to be solved.Especially for the rich potassium bauxite in some areas,potassium impurities enter into sodium aluminate solution during the dissolution process,which seriously affects the production of alumina with the continuous accumulation of Bayer cycle.In this paper,the effects of solution concentration,evaporation crystallization process and impurity ions on the performance of potassium removal by evaporation crystallization of sodium aluminate solution were systematically studied by means of XRD,SEM-EDS,PSD analysis and kinetic calculation,and the optimum process conditions were obtained.The results are as follows:The solubility of KmNanXOy in sodium aluminate solution were studied at different temperatures and concentrations of caustic concentration.Under the same conditions,the solubility of KmNanXOy in sodium aluminate solution increases with the increase of temperature and decreases with the increase of caustic concentration,the effect of temperature on solubility is not obvious under low caustic alkali concentration condition.The effects of X/K,caustic concentration,reaction temperature,reaction time and Cl-、carbonate impurity on the removal performance by evaporation crystallization of sodium aluminate potassium solution were studied by single factor control variable method.In the evaporation crystallization process,reducing the caustic concentration,increasing the crystallization temperature and prolonging the crystallization time are beneficial to improve the potassium removal rate of the solution aluminate.In the process of strengthening crystallization,increasing caustic concentration,decreasing crystallization temperature and shortening crystallization time are beneficial to the removal of potassium from sodium aluminate solution.The optimum conditions for potassium removal from sodium aluminate solution are determined as follows:the X/K is 2.00,the caustic concentration in the crystallization process is 200 g·L-1,the temperature is 95℃,and the time is 60 min;in the process of enhanced crystallization,the caustic concentration is 350 g·L-1,the temperature is 50℃,and the time is 20 min.The potassium removal rate under these conditions is more than 86%.The existence of Cl-and carbonate will reduce the potassium removal rate of the solution,and the carbonate impurities have a more obvious inhibitory effect on the potassium removal performance of the solution.As a result,the potassium removal rate of circulating mother liquor in alumina production site is only 40.90%under the optimum conditions.The growth mechanism under different conditions and crystal structure of KmNanXOy were studied.There are two kinds of precipitation forms of KmNanXOy in solution:spontaneous precipitation and precipitation induced by NaXOy as seed,and there is a dynamic process of precipitation and re-dissolution at the same time.When the strengthening crystallization time is 10min,the morphology of KmNanXOy crystal is hexagonal plate,embedded and gathered into irregular olive-shaped spherical particles.When the strengthening crystallization time is 20 min,the KmNanXOy crystal becomes hexagonal column,and the crystal gathers into large olive spherical particles with a small amount of hexagonal plate crystal distribution.When the strengthening crystallization time is 90 min,the KmNanXOy crystal gathers into round spherical particles,and the surface is no longer smooth.The existence of carbonate makes the KmNanXOy crystal become hexagonal flake and the aggregation mode becomes scattering.The kinetics of KmNanXOy formation in sodium aluminate solution was caculated.The chemical reaction of additive NaXOy and potassium aluminate in the solution is controlled by internal diffusion,and the reaction rate equation is as follows:1-2α/3-(1-α)2/3=0.52×exp[-16.13/(RT)]t。... |
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