Study On Recovery Of Iron From Bayer 's Red Mud By Reduction Roasting - Magnetic Separation

How to recycle valuable metals such as iron,aluminum effectively from red mud is one of the hot topics in the utilization of red mud.In this paper, red mud produced from Bayer process of some aluminum plant in Yunnan province has been studied. Elemental analysis, X-ray diffraction analysis, Scanning electron microscope analysis have been applied on the red mud sample to figure out composition of the ore. Gravity dressing, froth flotation and conventional magnetic dressing were tested in order to get ferrum out of red mud, the results proved them to be failed. Considering most of ferrum in red mud is contained in iron oxides, the process of carbothermal reduction combined with magnetic dressing was adopt. Further more, influences on dressing index of some factors, including roasting temperature, reduction time, the addition of additive, grinding fineness, the strength of the magnetic field, were studied.As was shown by the experiments, with the roasting temperature lower than900℃, both of the iron grade and iron recovery rate of the iron concentrate obtained by carbothermal reduction combined with magnetic dressing process were low, which indicated a bad dressing index of red mud. With the roasting temperature raised higher than1000℃and proper addtives, such as alkali metal compound, introduced into red mud, reduction rate of iron oxides increased, both iron grade and iron recovery rate of iron concentrate reached a higher level, due to higher CO density surrounding red mud roasted and higher reacting activity of FeO, respectively.As a result of the experiments, optimal dressing conditions were fixed as follow:roasting temperature of1250℃, roasting time of120min, carbon dosage of20%red mud mass, CaF2dosage of8%, Na2SO4dosage of6%, for roasting process and grinding fineness of90%particles passing400mesh sieve,exciting current of2.5A for magnetic dressing process. Under the optimum conditions, a iron concentrate with iron grade of85.54%and iron recovery rate of86.24%was obtained. As reduction roasting is the main processing that affects the dressing index, response surface method has been applied on optimizing experimental conditions for carbothermal reduction roasting process in order to get the most iron out of red mud. CCD(central composite design) has been used to study the influence of roasting time, roasting temperature and carbon dosage on iron oxides reduction and get optimal experimental conditions. As a result, experiments reveals that each of the three conditions has a significant influence on the dressing index and optimal experimental conditions are obtained as follow:roasting temperature of1225℃, roasting time of115min, carbon dosage of18%red mud mass. Under the optimal conditions, the stimulated dressing index is iron grade of86.07%and iron recovery rate of86.46%. In addition, a verification test is performed under the optimal conditions and a concentrate with iron grade of86.56%and iron recovery rate of86.90%is obtained, which shows a rather small difference to the stimulated value and indicates a successful optimization by using response surface method. Contracted with the dressing index obtained under un-optimized conditions, both iron grade and iron recovery rate of iron concentrate are raised slightly after experimental conditions are optimized by response surface method.The main compounend of iron concentrate is iron and slight amount of Al, Si, P, S, Ca. Iron concentrate can be used as charge of shaft furnace. The tailing can be used to produce construction materials such as baking-free bricks.