Study On Co-recovery Of Iron And Aluminum From Red Mud And Phosphogypsum Under The Action Of Carbon And Alkali

Phosphorus chemical industry and aluminum industry are the two pillar industries in China,and their production capacity is in the forefront of the world.However,it brings about problems such as large annual production of phosphogypsum and red mud industrial solid wastes,low utilization rate and high environmental stacking pressure.Therefore,it is urgent to increase their large-scale comprehensive utilization.At present,phosphogypsum and red mud are mostly used alone,and mainly in primary utilization methods such as cement,concrete,brick and filling.It is difficult to break through the bottleneck of large-scale and high value-added comprehensive utilization.Phosphogypsum is an acid slag.At present,there is a mature process of phosphogypsum sintering to produce sulfuric acid and cement,but a large amount of Si O₂ needs to be added in the sintering process.There is a mature alkali lime sintering process for producing alumina from red mud by adding a large amount of Ca O.Therefore,this paper adopts the process of red mud and phosphogypsum co-reduction roasting leaching magnetic separation to separate aluminum and iron from red mud.The theory and technology of aluminum and iron recovery from red mud were systematically studied.The effects of sintering temperature,sintering time,sintering atmosphere,alkali ratio,calcium ratio and grinding particle size on the recovery of aluminum and iron from red mud were discussed.At the same time,on the basis of the best process conditions,the comparative experiment was carried out by replacing phosphogypsum with lime and the traditional alkali lime sintering method.The optimum sintering conditions are as follows:temperature 1100℃,time 30min,atmosphere N₂,alkali ratio 1.3,carbon ratio 2.5,calcium ratio 2.0.Magnetic separation adopts hierarchical magnetic separation:the first magnetic separation current is 2A,and the magnetic slag selected for the first time is broken and then the second magnetic separation current is 1A.The experimental results of the optimal process are as follows:aluminum recovery is 74.6%,iron recovery is 78.2%,and iron grade is 83.8%.S of phosphogypsum and red mud reduction roasting products mainly exists in the form of Ca S.Under the condition of reducing agent,the decomposition of phosphogypsum into Ca S is easier than that of Ca O.In the presence of reducing agent and sodium carbonate,Ca S in the final product is formed by direct decomposition of phosphogypsum and decomposition of intermediate product Na₂SO₄.The comparison experiment between phosphogypsum and lime shows that the recovery index of aluminum and iron in phosphogypsum group is better than that in lime group,and the iron grade in phosphogypsum group is 34.4%higher than that in lime group.The results show that Na₂SO₄ produced by phosphogypsum is helpful to the reduction of iron oxides and the growth of iron grains.