Comprehensive Utilization Of Aluminum And Iron In Gibbsitic Bauxite Rich In Iron And Silicon From Guang-xi

There is a large amount of gibbsitic bauxite rich in iron and silica in Guang-xi Autonomous Region. It is an important potential resource for iron and alumina. In order to utilize the ore comprehensively,"iron after aluminum" process was developed. The digestion conditions, the effect of alumogoethite in digestion process, and the enrichment method of iron from red mud were investigated.To achieve high digestion rate of Al2O3and enrich the iron in red mud in Bayer digestion process, the influences of digestion temperature, time, caustic concentration and caustic ratio of Na2O to Al2O3of spent liquor and additives on the aluminum and silicon-bearing minerals reaction behaviors were investigated. The results show as follows:(1) Increasing digestion temperature and caustic concentration of spent liquor are benefit for the improvement of digestion rate of Al2O3. The soluble alumina in ore can be digested within-10minutes under appropriate temperature and spent liquor conditions.(2) The content of sodium aluminosilicate hydrate in red mud increases with the digestion temperature increasing and digestion time prolonging, which can cause the reduction of iron grade in red mud. Low molecule ratio of Na2Ok to Al2O3or adding additives can’t result in high Al2O3digestion rate and low sodium-silicon slag content red mud simultaneously.(3) The solubility of SiO2is enhanced with the increasing of caustic concentration of spent liquor under high temperature, which restrains the formation of sodium-silicon slag in digestion process;(4) The optimum digestion conditions of the gibbsitic bauxite at low temperatue are as following:digestion temperature is100～110℃, digestion time is10-20min, the caustic concentration of spent liquor is above150g/LPhase analysis of the bauxite and red mud by XRD analysis indicate a part of alumium exist as alumogoethite in the gibbsitic bauxite, alumogoethite can’t be digested under normal pressure, which may result in low digestion rate of Al2O3. It was found that non-calcareous additives can induce the transformation of goethite (or alumogoethite) to magnetite, which influence the digestion rate of alumina obviously. When the alumogoethite transformed completely, the relative digestion rate of Al2O3can reach100%.At last, the enrichment of iron from red mud was studied preliminarily on the basis of the character of red mud got by normal pressure digestion. Two technologies were put forward. One technology is re-digestion of the red mud at high temperature, followed by enrichment of iron via gravity separation of the re-digested red mud. Under the conditions of high digestion temperature (200～260℃) and caustic concentration of spent liquor (200～300g/L), Al and Si in the red mud are further digested which enables the enrichment of iron during the high temperature re-digestion process. Single mineral grains are also obtained through structure recombination of intertwined ores in the red mud, which benefits the gravity separation process. The other one is that red mud is magnetized at digestion process and then iron concentrate is obtained through magnetic separation. In magnetizing digestion process, weak magnetic iron-bearing minerals transform to magnetite which is strongly magnetic by adding non-calcareous additives in digestion process at236℃. And then iron concentrate can be obtained by magnetic separation. The two technologies have been proved to be feasible by experiments, but specific conditions need further optimization and perfection.