Study On Recovery Of Iron From Red Mud In Bayer Process By Direct Reduction - Magnetic Separation

Red mud, a waste residue produced in alumina production, is a type of red alkaline solid waste. Red mud is also one kind of important secondary resources which has large output. The recovery of value elements from the red mud is not only can bring economic benefits but also will be helpful the subsequent comprehensive utilization. In this paper, red mud produced from Bayer process of Wenshan aluminum plant in Yunnan province has been studied. Multi-element analysis, phase analysis, sieve analysis and elutriation experiment, SEM analysis and thermal analysis were used for analyzing the property of the red mud. Based on the property of red mud, direct reduction roasting-magnetic separation and reaction behavior of red mud were studied.In this paper, the best response condition of each factors was determined. The best conditions as following:roasting temperature 1150℃, roasting time 120 min, mass ratio of activated carbon:red mud=19:100, mass ratio of NaF:red mud=12:100, mass ratio of CaF2:red mud=12:100, cooling system is water quenching, grinding 10 min with wet rod mill (-400 mesh 96.56%), magnetic field intensity 1940 Oe. Then, orthogonal experiment showed the influence degree of five factors to concentrate recovery from big to small as following:roasting temperature, NaF quantity, roasting time, activated carbon quantity, CaF2 quantity. And under the best combination of conditions, it can get the 81.75% iron concentrate with 85.96% recovery by using magnetic tube and the degree of tailings is 4.05%. By using magnetism barrel with the same roasting conditions under 1200 Oe magnetic field intensity, it can get the 56.83% iron concentrate with 78.17% recovery and the degree of tailings is 5.43%.The reduction behavior of roasted products shows that reduction effect of anthracite is similar to activated carbon. As to activated carbon, the iron dispersed irregular among crystalline solid with different sizes of spherical, which is benefit to monomer dissociation in the subsequent grinding. For reducing temperature, it has a significant effect on the reduction behavior of red mud. The Fe concentration increased and the Al and Si concentration decreased in crystalline solid with the reducing temperatures improved. Besides, different additives had different effects on the enrichment of iron. The results showed that NaF and CaF2 can both promote the iron enrichment and reduction significantly. Adding NaF can improve the crystallization of iron in red mud and the density of iron concentrate, so it can get the higher grade of iron(74.95%). Adding CaF2 can let iron crystals become coarse and exist in the form of pellet. After partial enlarged, it can be seen that multiple cracks is distributed in the iron crystals which was beneficial to the latter monomer dissociation, so it can get higher recovery of iron(81.79%).Under the best roasting conditions, the iron in red mud crystallize into large spherical particles and the other region exists little iron, which shows it has good enrichment effects. Ferrous phases of direct reduced products showed that most of hematite and limonite were transformed into corresponding magnetic iron, and the transformation rate could exceed 99%. The XRD pattern of magnetic concentration shows that the characteristic peak of iron elemental is obvious and without other obvious impure peaks, which demonstrated the iron minerals, such as hematite and limonite were reduced into metallic iron during the direct reduction.