Study On Leaching Of Red Mud With Titanium Dioxide Waste Acid And Precipitation/Polymerization Recovery Of Aluminum And Iron From The Leaching Solution

Red mud is a kind of solid waste discharged during the production of alumina from bauxite,which has a huge hazard on the environment due to its strong alkalinity.And as a kind of secondary mineral resource,red mud is enriched with valuable metal elements,of which iron and aluminum oxides account for about 40%of the total components.Titanium dioxide waste acid is a kind of liquid waste discharged during the production of Ti O₂by the sulfuric acid process,which is highly acidic and contains a high content of Fe²⁺,resulting in a difficult recycling process.In this paper,the leaching solution was obtained by leaching red mud with titanium dioxide waste acid,and then aluminum and iron in the leaching solution were recovered by Ferrous Oxalate recovery method and Polymeric Aluminum Ferric Sulfate recovery method,which not only had a certain resource recovery value,but also achieved the purpose of“treating waste with waste”.In this study,the mineralogy of the red mud was first conducted,and the main occurrence states of iron and aluminum in the red mud were identified to be Hematite and Cancrinite,Hibschite and Gibbsite,respectively.The best experimental conditions for leaching were determined by acid leaching experiments:red mud roasting temperature of 900°C,reactants L/S ratio of 8:1,leaching temperature of40°C and reaction time of 1 h.And the leaching rates of Al₂O₃and Fe₂O₃in the red mud reached 58.32%and 42.35%,respectively,under these operating conditions.Then,the recovery of Ferrous Oxalate and the preparation of Polymeric Aluminum Ferric Sulfate were proposed for the high concentration of iron and aluminum ions in the leaching solution.In the recovery of ferrous oxalate,it was determined by speciation analysis that in H₂C₂O₄-H₂SO₄system Fe（II）exists as mainly Fe²⁺and Fe C₂O₄.Ferrous oxalate was recovered by adding Na₂C₂O₄to 50 m L of leaching solution,and the content of Na HC₂O₄·H₂O impurities in the product was reduced by increasing the reaction temperature.The precipitation rate of Fe（II）reached 85.54%under the conditions of Na₂C₂O₄dosage of 16 g,reaction temperature of 100°C,stirring speed of 300 rpm and reaction time of 1 h.Finally,Fe C₂O₄·2H₂O with a purity of 99.05%was purified by washing with concentrated phosphoric acid,saturated（NH₄）₂C₂O₄solution and deionized water.In addition,Na₂SO₄was obtained by cooling and crystallizing from the filtrate.According to the study on the preparation of PAFS,the polymerization mechanism of Al（III）and Fe（III）was explored as follows:Fe³⁺is hydrolyzed preferentially,while Al³⁺is bonded to the completed polymerization Fe³⁺by hydroxyl,and Al³⁺has a certain promotion effect on the hydrolysis of Fe³⁺.In addition,the increase of Al/Fe ratio can change the hydrolysis tendency of Al³⁺,while the increase of basicity value can improve the content of high polymers in the product,which affects its performance.The flocculation experiments showed that:the medium polymers were the active substances with the greatest influence on the treatment capacity of the simulated wastewater,the low polymers had a strong charge neutralization ability,while the treatment machanism of the high polymers were more mechanically oriented.Finally,the best performing Titanium Dioxide Waste Acid-Red Mud Polymeric Aluminum Ferric Sulfate product was prepared by adjusting Al/Fe ratio to 10:5 at 80%basicity using leaching solution as raw material,with the content of low,medium and high polymers were 42.46%,21.68%and35.86%,respectively,and the turbidity and chromaticity removal rates reached96.32%and 95.06%for the high turbidity simulated wastewater and high chromaticity simulated wastewater,respectively.