Study On Two-Stage Acid Leaching Process Of Alumina And Iron Oxide From Guangxi Pingguo Alumina Corporation Produced Red Mud

Bayer red mud from Pingguo Aluminum Corporation in Guangxi, as a kind of solid waste which is produced in the alumina production, causes severe environmental pollution and puts enormous pressure on the environment due to its high alkaline and complex constituents. So it is important to recycle it. The Bayer red mud from Pingguo Alumina Corporation in Guangxi contains a great deal of alumina and iron oxide thus it is significant to recover aluminum and iron from it.In this study, two-step acid leaching technology, which is alumina and iron oxide was leached from Bayer red mud by nitric acid and hydrochloric acid, was used to extract aluminum and iron from red mud from Pingguo Aluminum Corporation in Guangxi, respectively. The effects of influencing factors such as leaching temperature, leaching time, liquid to solid ratio and acid concentrate on leaching rate of alumina and iron oxide were investigated through four factors-four levels and four factors-five levels orthogonal tests. The results show:1) Under constant pressure, the optimum technological conditions for alumina leaching by nitric acid from Bayer red mud are at the temperature of boiling point, nitric acid concentrate of8mol/L and liquid to solid ratio of6:1for90min;2) Under constant pressure, the optimum technological conditions for iron oxide leaching by hydrochloric acid are at the temperature of boiling point, hydrochloric acid concentrate of7mol/L and liquid to solid ratio of6:1for90min.However, after these results were verified and adjusted via simple variable method, it is found that the optimum technological conditions for alumina leaching need revising, that is to say, the optimum concentrate of nitric acid should be set at7mol/L rather than8mol/L while other conditions remain unchanged. Under the revised optimum conditions, the leaching rate of alumina and iron oxide is64.3%and99.47%, respectively.The reaction model was established based on the interaction between capillary liquid and porous solid to fit the relationship between the leaching rates and leaching time of alumina and iron oxide, and predict their tendency. The results indicate under the experimental conditions, the ideal leaching rate of alumina and iron oxide is63.65%and97.65%respectively, which agrees well with the leaching rate under the optimum conditions.The leaching rates of alumina and iron oxide under the optimum condition and the reaction model were validated and interpreted by contrasting the physical phase of red mud from Pingguo Aluminum Corporation in Guangxi and acid leaching residue.Finally, the optimum technological conditions, which is alumina leached from red mud by hydrochloric acid, was used to extract iron from waste red mud slag, which was from the red mud leached by hydrochloric acid under the optimum leaching technological conditions, with hydrochloric acid leaching. The test results show that the leaching rate of alumina and iron oxide reaches4.55%and91.87%, respectively.