Research On The New Technology For Preparing Potassium Sulfate From Potassium Alum And Its Comprehensive Utilization

Potassium sulfate is an important non-chlorine potash fertilizer in potash fertilizer which is one of the three agricultural fertilizers.The water-soluble potassium salts reserves in our country are low,causing a long-term dependence on import.Therefore,it is of great significance to prepare potassium sulfate with abundant non-water-soluble potassium ores.We have made a long-term study on the methods,e.g.alunite directly pressure acid-leaching,potash feldspar fluorochemical method and lepidolite fluorochemical method,to prepare potassium sulfate by water-insoluble potassium mineral resources.And we proposed a new technology route of separating potassium and aluminum by crystalization of potassium alum from the acid leaching solution.The novel technology has exploited a new approach for the development and utilization of water insoluble potassium mineral resources.Thus,a study on the comprehensive utilization of potassium alum will be of great significance.The process of preparing potassium sulfate and aluminum chloride by double decomposition with potassium alum and muriate was put forward.And the physical property analysis of metathetical reaction showed that the double decomposition reaction temperature should be higher than 60 ?.The process of replacement reaction was studied and the factors that influence the formation of potassium sulfate were analyzed by single factor optimization,and the optimum conditions were as follows:reaction temperature 90 ?,potassium alum/muriate molar ratios of 1:4.4,salt/water mass ratios of 1.45:1,reaction time 120 min and shock rate 150r/min.Meanwhile,the crystallized product was 7.83 g and the purity of potassium sulfate was 75.69%.The rest was potassium chloride.Therefore,a further recrystallization is needed to obtain pure potassium sulfate.Above experimental results indicate that the technical route of double decomposition reaction about potassium alum and potassium chloride is feasible to get potassium sulfate.The liquid-solid phase equilibria of quatellary reciprocal system K+,Al3+//SO42-,Cl--H2O was studied by isothermal solution equilibrium method at 90?.According to the analysis of phase diagram,the system point formed by potassium alum and muriate could fall in the potassium sulfate crystal phase area.Pure potassium sulfate crystal can be obtained by double decomposition in theory,but the potassium sulfate crystallization area is small at 90?.So it is very difficult to get pure potassium sulfate directly by double decomposition at this temperature.The metathesis reaction process of potassium alum and potassium chloride was proposed and studied at temperatures ?100?.And it was found that basic potassium aluminum sulfate was easy to be obtained but potassium sulfate was difficult to be gotten under high temperature conditions.When the reaction was carried out with dilute sulfuric acid as the solvent,however the potassium sulfate still was not obtained when the AG was as high as 14.64.The solid phase was basic potassium aluminum sulfate because that Al3+ was easily hydrolyzed to make the solution be acidic under high temperature conditions.Neverthless,Cl-in the acidic solution was easily converted into HCl volatilizing from the system at high temperature.Therefore,it is not easy to produce potassium sulfate with potassium alum at temperatures ?100?.The double decomposition of potassium alum in ethanol-water mixed solvent was put forward and studied.And the research showed that the solubility of potassium sulfate was greatly reduced in the ethanol-water mixed solvent.According to the study on the process of double decomposition reaction and the single factor optimization analysis of factors that influence the formation of potassium sulfate,the optimum conditions were as follows:the mixed solvent containing 40 wt.%ethanol,reaction temperature 70?,potassium alum/muriate mass ratios of 1.8:1,salt/water mass ratios of 0.7:1,shock rate 200 r/min and reaction time 120 min.The quality of the crystallized products was 25.86 g and the purity of potassium sulfate was 91.71%under above optimal conditions.This study provides a theoretical foundation and basis for the preparation of potassium sulfate and aluminum chloride by double decomposition using potassium alum and potassium chloride.And the study has opened up a new direction for solving the problem of extracting potassium fertilizer from insoluble potassium ore and comprehensive utilization of resources.Therefore,it is of great strategic significance to expand the range of available potassium resources in the world.