Study On Preparation Of Ultrafine Alumina Powder By Alunite Acid-base Combined Method

Our country has abundant reserves of alumite mineral resources,which have been proven about 300 million tons,ranking among the top in the world.Alumite mainly contains aluminum,potassium and sulfur elements,the extraction of valuable elements and comprehensive utilization of alumite is one of the research hotspots in the industry.As a major agricultural production country,our country is always in short supply of potash fertilizers and belongs to a potassium-deficient country;at the same time,as a major alumina producer,my country still needs to import a large amount of bauxite every year to meet the needs of industrial production.Therefore,how to comprehensively utilize alunite to prepare potash fertilizer and alumina is highly responsible for practical application value.This thesis mainly focuses on the comprehensive utilization of alumite with high added value,and uses alumite as raw material to obtain the process conditions for the step-by-step extraction of potassium and aluminum elements through single-factor experiments.The effect of process conditions on the extraction rates of potassium and aluminum was investigated.The extraction of potassium from alumite was optimized by response surface methodology.By studying the kinetics of the potassium leaching process from alumite,it was determined that the reaction was controlled by chemical reactions process.The solution containing aluminum ammonium sulfate obtained after extracting aluminum was reacted with ammonium bicarbonate,and the main research results of ultra-fine alumina powder material were prepared through precipitation and main research results are as follows:(1)Increasing the leaching temperature,time,potassium hydroxide concentration,and molar ratio of alunite to potassium hydroxide had a significant effect on the increase of potassium extraction rate.The response surface method showed that the extraction rate of potassium element reached 99.15% under the conditions of leaching temperature of 86 ℃,leaching time of 90 min and potassium hydroxide concentration of 11%.This leaching process accompanied by apparent activation energy of 76 k J/mol.(2)Under the conditions that the leaching temperature was 95 ℃,the leaching time was2 h,the concentration of ammonium hydrogen sulfate was 60%,and the molar ratio of ammonium hydrogen sulfate to potassium extraction solid phase residue was 3,the extraction rate of aluminum element reached 95.46%.The median diameter of the final prepared alumina powder material was 5.538 μm,which belongs to the ultrafine powder material.