Experimental Study Of High-Alumina Fly Ash For Acid Extraction And Separation Of Calcium And Aluminum

At present,the contradiction between supply and demand in China was serious,and the bauxite congenital storage was insufficient.The content of alumina in high alumina fly ash was 30%～50%,which is equivalent to the content of middle low grade bauxite Al₂O₃ in China.As an important potential resource of producing alumina,it is of great strategic significance and ecological benefit to extracting the Al₂O₃ from high alumina fly ash.At this stage,extracting alumina from high alumina fly ash mainly was alkali method,but it requires high temperature,high energy consumption,long process,and brings a large amount of slag.The extracting alumina by acid process has advantages of short process and high resource extraction rate.In this paper,extracting alumina from high aluminum powder fly ash by the method of acid process,and decalcifing in leachate treatment was carried out in-depth study and explore.Alumina content of high alumina fly ash was more than 50%,showing the characteristics of high aluminum content.High alumina fly ash has less crystalline mineral,it mainly include gypsum,quartz,andalusite and hematite,most of the alumina are amorphous.Leaching under 170 ℃ 180 min,32%hydrochloric acid and acid ash ratio 2.5 ml/g,the leaching rate of alumina was 76.04%.The leaching effect of alumina by mixed acid of HCl-H₂SO₄ system is better than that of HCl-H₃PO₄ system.With sodium acetate as inhibiting calcium,n（CH₃COONa）/n（Ca）= 0.5,under 700℃,roasting 2.0h and then leaching under the condition of 32%HCl,170℃,3.0h,alumina leaching rate reached 90.12%,calcium oxide leaching rate reached 99.74.Sodium acetate mixed roasting is no obvious inhibitory effect of calcium.The hydrochloric acid leaching solution of high alumina ash was concentrated,crystallized and calcined so as to produce primary alumina.The primary alumina after 0.7mol/L hydrochloric acid washing,alumina decalcification rate up to 96.32%.According to the filtrate of the factory production,the leaching solution was simulated.Sodium phosphate of calcium removal effect is the best.When the filling ratio was 0.9,the calcium removal rate reached 91.9%,aluminum loss rate was below 10%.In actual leaching solution test,when the dosage of filling ratio in 0.9,the precipitation rate of calcium was 87.9%and aluminum loss rate was 11.6%,indicating that sodium phosphate on the leaching solution in addition to calcium plays the important role.