Effect Of Magnetization Roasting On Mineral Phase Structure And Dissolution Properties Of Wenshan High Iron Bauxite

Most of the bauxite resources in China are diaspore bauxite,and the high-quality bauxite resources are decreasing day by day.42%of the bauxite alumina to silica ratio(A/S)is lower than5,which is not suitable for the Bayer digestion.High-iron bauxite is a typical complex bauxite.The current research mainly focuses on methods such as"aluminum and iron separation","aluminum before iron"and"iron before aluminum".This paper takes Wenshan high-iron bauxite as the research object,adopts"aluminum before iron",that is,a method of magnetic-roasting and high-pressure digestion under static conditions,focuses on the influence of magnetic-roasting on the evolution of the phase structure and the digestion mechanism,and it will be verified through the effect of red mud magnetic separation.The main conclusions are as follows:(1)The original bauxite has a dense structure,complex distribution of aluminum and iron,and it is difficult to separate and recover.After magnetic-roasting,the chemical composition and bauxite structure changed significantly.The magnetic susceptibility of bauxite decreases with the increase of the magnetic-roasting temperature,the extension of the H₂ injection time and the increase of the H₂ concentration,the A/S of bauxite is relatively stable.During the magnetic-roasting process,the diaspore contained in the bauxite is dehydrated and transformed into a?-alumina with a certain activity,and the iron-containing mineral is transformed into Fe₃O₄.The magnetic-roasting temperature is too high,and the H₂ injection time and concentration increase.Both will cause iron-containing minerals to undergo a reduction reaction and produce Fe₂Si O₄.Both the dehydration reaction of diaspore and the reduction reaction of iron-containing minerals will produce H₂O,which will escape in the form of vapor,resulting in the formation of a large number of crack in the bauxite and an increase in the specific surface area.The kinetic calculation results show that the magnetic transformation of iron-bearing minerals is limited by the internal diffusion;(2)Under the conditions of digestion temperature of 260?,digestion time of 60min,lime addition of 12%,and caustic alkali concentration of 245g/L,the relative digestion rate of alumina is only 84.92%.After the bauxite is treated with optimal magnetic-roasting conditions:roasting temperature of 530°C,H₂ injection time of 5 minutes,and H₂ concentration of 20%,under the above digestion conditions,the relative digestion rate of alumina reaches 95.47%;other conditions remain unchanged,when lime is added to 10%,the relative digestion rate of alumina of the magnetic-roasted bauxite increases to 98.78%.(3)The Fe₂Si O₄ generated in the bauxite during the magnetic-roasting process reacts with Na OH during the Bayer digestion process to increase alkali consumption,and enters the red mud in the form of iron hydrogarnet.The magnetic separation test results show that the magnetic separation performance of the red mud after Bayer digestion is better than that of the magnetic-roasted bauxite.A large amount of alumina is digested during Bayer digestion,which is beneficial to the separation of aluminum and iron.The optimal process parameters of the red mud magnetic separation experiment are:magnetic field strength 2A/m,particle size 200 mesh,liquid-solid ratio 30:1,the iron recovery rate of the red mud magnetic separation under these conditions is 88.48%,and the concentrate TFe 40.35%,which is an increase of 1.72 times compared with 23.35%of the TFe of red mud.