Research On The Comprehensive Recovery Of Aluminum And Iron From The Bayer Process Red Mud

Red mud is an industrial waste residue produced in alumina production process.It has the characteristics of fine granularity,complex composition,high radioactivity and strong alkalinity,thus causing environmental problems,such as soil alkalization,groundwater pollution,atmospheric pollution,radioactive pollution.Besides,it has the risk of dam-break.However,red mud,at the same time,contains iron,aluminum,titanium,sodium and a variety of rare earth elements,which is a valuable secondary resource.In this paper,the red mud of Pingguo aluminum-Bayer process in Guangxi was taken as the experimental object.On the basis of certain mineralogical analysis,the process of“reduction?alkaline?roasting-alkali leaching-magnetic separation”was adopted to recover the aluminum and iron from red mud comprehensively.The main conclusions are as follows:1.The technological mineralogical characteristics of red mud from bayer process were investigated in this paper.The results shows that the total iron content of red mud used in the test is 24.32%.It mainly exits in the form of Fe₂O₃?hematite?and?-FeO?OH??goethite?,and the distribution of the former is much higher.The content of Al₂O₃ in red mud is 16.90%and Al is mainly in the form of AlOOH?diaspore?and Al?OH?₃?aluminum hydroxide?,and some Fe and Al exist in the form of isomorphism in Ca₃(Al_0.13Fe_0.87)₂?SiO₄?_1.15?OH?_5.4?hydrated garnet?.The beneficial elements in red mud are mainly iron,aluminum,titanium.The gangue and slagging elements are mainly silicon dioxide and calcium oxide.The particle size of red mud by Bayer method is fine,particle size of-45?m counts for 72.87%in which the distribution of iron is 66.44%.2.The effects of various factors on the extraction of aluminum and iron in red mud during“reduction?alkaline?roasting-alkali leaching-magnetic separation”process were clarified in this paper,and the optimum technological conditions for comprehensive recovery of aluminum and iron from red mud were determined.Research shows that the leaching rate of aluminium can reach 88.37%,and the iron concentrate of 83.38%grade and 72.46%recovery can be be obtained by“reduction?alkaline?roasting-alkali leaching-magnetic separation”process under the optimum conditions as follows:addition amount of 5 g·?100 g red mud?^-1 CaO,15 g·?100 g red mud?^-1 Na₂CO₃,and 15 g·?100 g red mud?^-1 actived carbon powder,roasting temperature of 1150?,roasting time of 60 min,cooling mode of water quenching,grinding fineness of 95.84%-0.038mm?grinding time 30 min?and exciting current of5A?1370Oe?.3.The phase transformation of the main elements during the roasting process were studied in this paper.It was found that under appropriate proportion of calcium oxide,sodium carbonate and activated carbon,after reduction?alkaline?roasting,the aluminum in red mud mainly converts to soluble sodium aluminate,and iron was reduced to strong magnetic metallic iron and part magnetic iron.While silicon mainly transforms calcium silicate,which laid the foundation for the subsequent separation of silicon,aluminum and iron.