Research On Optimization Of Utilizing Alunite Tailings Comprehensively By Pressure Acid Leaching

In this study,a novel process was proposed for the comprehensive utilization of alumite tailings floated from the tailings of Zijin copper ore by acid-leaching under low pressure,which makes the industrial application of alumite tailings more promising.On the basis of the previous study for utilizing alunite by non-roasting acid-leaching under pressure,the leaching pressure was reduced dramatically,the leaching conditions were further optimized and,in the meanwhile,the valuable components were extracted high-efficiently.In addition,the pathway of gallium during leaching process was also investigated,which could provide theoretical and experimental support for the utilization of gallium.Through the study of the acid leaching of alumite tailings under low pressure(?1.0 MPa),the leaching conditions were optimized.The optimum extraction conditions were as follows:acid ratio 5:1,reaction temperature 160?,reaction time 6h,initial acid concentration 50%,stirring speed 600r/min.Under the optimized leaching conditions,the leaching efficiencies of potassium,aluminum and gallium reached 99.13%,99.19%and 98.69%,respectively.Comparing with the leaching under medium-pressure,the method of low pressure acid-leaching has the following characteristics:1)the reaction pressure was reduced from 1.8MPa to 0.6MPa,the leaching rate of each component in alunite was as same as that of high pressure leaching;2)the scattered metal-gallium contained in the alunite tailings was extracted effectively and can be enriched by the circulation of post-crystallized mother liquor;3)the excess sulfuric acid introduced during the acid leaching process could be recovered by recycling the post-crystallized mother liquor,and acid consumption in the process was very close to the theoretical consumption,which indicates a low material consumption process;4)the composition of the insoluble residue was more simple which benefits the further recovery process.The investigation of the gallium's pathway in the leaching solution indicates that more than 98%gallium in the alumite was converted into soluble sulphate going into solution.The phase equilibria in the ternary systems K2SO4-Ga2(SO4)3-H20 and Al2(SO4)3-Ga2(SO4)3-H2O at 5? showed that Ga2(SO4)3 and K2SO4 did not form double salts.Therefore,the K2SO4 and Ga2(SO4)3 in the leaching solution does not form gallium potassium alum,and potassium alum will not be mixed with gallium potassium.Thus,the gallium can be enriched and recovered by the circulation of mother liquor.By using the SEM,XRD and granulometer methods,the structure and composition of alunite tailings were analyzed and determined.The results showed that crystal structure of the mineral-alunite was destroyed effectively by sulfuric acid,and the metals reacted with sulfuric acid and were recovered as soluble sulphate.The insoluble residue as the major component of the silica,with particle size of 500 mesh,could be used as the value-added product of silicon material.This process eventually enables the efficient utilization of all major components contained in the alunite tailings.Additionally,the costs analysis of the proposed process shows that the gross profit rate reached around 113%,which indicates the process has promising prospect for industrial application.