Aluminum products are one of the most widely used metals. The current output and consumption of aluminum (in tons) is second only to steel and has become the second-largest metal for human application.
Bauxite is mainly used to extract aluminum. About 85% of bauxite can be refined into alumina and then smelted into aluminum, 8% for chemical alumina, and 7% for refractory materials, proppants, and cement.
Ore washing is the simplest and most effective method to improve the bauxite aluminum-silicon ratio by about 2 times. But you need to combine the ore washing process with other methods including classification -Manual selection process.
3Control the concentration of the pulp, adjust the parameters of the classification equipment to achieve the separation of coarse and fine particles, and reduce the lower limit of recycled particle size.
1Because collecting agent contains the surface-active substances, the foam of each operation of bauxite flotation is very sticking and big-volume. So, the general quantity of water will consume alarge amount of foam flushing waters, finally reducing the concentration of the flotation system.
In addition to aluminum and iron minerals, high iron bauxite is also accompanied by valuable metals such as gallium and vanadium, of which Ga content is 0.0044% ~ 0.0070%, V205 content is 0.148% ~ 0178%.
1However, the content of aluminum and iron is relatively low so that whether it is a single aluminum ore or a single iron ore, it is difficult to meet the basic requirements of industrial applications.
2Besides, the iron and aluminum minerals are embedded in a very fine grain size. Most minerals are poorly crystallized, some are colloidal and cemented with each other, and the embedding relationship is extremely complicated.
The chemical method means that we should fully dissociate aluminum minerals and silicon minerals in bauxite. The physical method uses classification equipment for bauxite concentrate. Outstanding features of the combination of the two ways:
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Aluminum is the most common metal element found on Earth, totaling about 8% of the Earths crust. However, aluminum as an element is reactive and therefore does not occur naturally it needs to be refined to produce aluminum metal. The primary starting material for aluminum refining is bauxite, the worlds main commercial source of aluminum. Bauxite is a sedimentary rock, and consists mostly of the aluminium minerals gibbsite (Al(OH)3), boehmite (-AlO(OH)) and diaspore (-AlO(OH)), and is usually mixed with the two iron oxides goethite and hematite, the aluminium clay mineral kaolinite and small amounts of anatase (TiO2) and/or ilmenite (FeTiO3).
Bauxite deposits are spread worldwide, mostly occurring in tropical or subtropical regions. Although proven reserves of bauxite are expected to last for many years, the quality of the reserves that can be economically accessed is declining. For refiners, who are in the business of processing bauxite to make alumina, and eventually aluminum metal, this is a challenge with both financial and environmental implications.
The most widely used chemical process of refining bauxite into alumina, the Bayer process, involves dissolving the Al2O3 out of the bauxite rock with caustic soda (NaOH) at elevated temperature and pressure. The Al2O3 fraction of the bauxite is dissolved into solution, to later be precipitated out as alumina. However, a high-grade bauxite contains up to 60% Al2O3, and many operating bauxite deposits are well below this, occasionally as low as 30-40% Al2O3. Because the desired product is a high purity Al2O3, the remaining oxides in the bauxite (Fe2O3, SiO2, TiO2, Organic material) are separated from the Al2O3 and rejected as alumina refinery resides (ARR) or red mud. In general, the lower quality the bauxite (ie lower Al2O3 content) the more red mud is generated per ton of alumina product. In addition, even some Al2O3 bearing minerals, notably kaolinite, produce un-desirable side reactions during the refining process and lead to an increase in red mud generation, as well as a loss of expensive caustic soda chemical, a large variable cost in the bauxite refining process.
Red mud or ARR represents a large and on-going challenge for the aluminum industry. Red mud contains significant residual caustic chemical leftover from the refining process, and is highly alkaline, often with a pH of 10 13. It is generated in large volumes worldwide according to the USGS, estimated global alumina production was 121 million tons in 2016. This likely resulted in more than 150 million tons of red mud generated during the same period. Despite ongoing research, red mud currently has few commercially viable paths to beneficial re-use. It is estimated that very little of red mud is beneficially re-used worldwide. Instead the red mud is pumped from the alumina refinery into storage impoundments or landfills, where it is stored and monitored at large cost.
The loss of expensive caustic soda (NaOH) and the generation of red mud are both related to the quality of the bauxite used in the refining process. In general, the lower the Al2O3 content of the bauxite, the larger the volume of red mud that will be generated, as the non-Al2O3 phases are rejected as red mud. In addition, the higher the kaolinite or reactive silica content of the bauxite, the more red mud will be generated. The reactive silica content not only increases the volume of red mud, but also consumes caustic soda reagent and reduces the yield of Al2O3 recovered from the bauxite. Therefore, there is both an economic and environmental argument to be made for improving the quality of bauxite prior to refining.
The STET dry separation process offers bauxite producers or bauxite refiners an opportunity to perform pre-Bayer-process upgrading of bauxite ore to improve the quality. This approach has many benefits:
In summary, dry processing with the STET separator offers opportunities to generate value for bauxite producers and refiners. The pre-processing of bauxite prior to refining will reduce chemical costs, lower the volume of red mud generated and minimize process upsets.
ST Equipment & Technology (STET) was founded in 1989, but at the time was known only as ST, abbreviated from Separation Technology. Specializing in the commercial triboelectrostatic separation process initially
AGB2A, a Guinea based company, produces one of the best metallurgical grade bauxite for alumina refinery by dry beneficiation process involving crushing and screening of ore. GBT bauxite is unique and different from usual Guinea bauxite as these are embedded in the silica rich fines at the periphery of hillocks. This is the first project in Guinea to beneficiate bauxite ore at the mine site and export high quality ore. The XRF, quantitative mineralogical analysis and bomb digestion tests showed that this is an ideal bauxite for low temperature alumina refinery. Beneficiated lumpy bauxite has fairly high available alumina (44-46% in average) and low reactive silica 1.2 to 1.4 with less than 1% boehmite.
A low grade bauxite sample of central India was thoroughly characterized with the help of stereomicroscope, reflected light microscope and electron microscope using QEMSCAN. A few hand picked samples were collected from different places of the mine and were subjected to geochemical characterization studies. The geochemical studies indicated that most of the samples contain high silica and low alumina, except a few which are high grade. Mineralogically the samples consist of bauxite (gibbsite and boehmite), ferruginous mineral phases (goethite and hematite), clay and silicate (quartz), and titanium bearing minerals like rutile and ilmenite. Majority of the gibbsite, boehmite and gibbsitic oolites contain clay, quartz and iron and titanium mineral phases within the sample as inclusions. The sample on an average contains 39.1% Al2O3 and 12.3% SiO2, and 20.08% of Fe2O3. Beneficiation techniques like size classification, sorting, scrubbing, hydrocyclone and magnetic separation were employed to reduce the silica content suitable for Bayer process. The studies indicated that, 50% by weight with 41% Al2O3 containing less than 5% SiO2 could be achieved. The finer sized sample after physical beneficiation still contains high silica due to complex mineralogical associations.
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G.V.K. Puvvada, B.V.S. Yedavalli, A.S. Rao, Solvent extraction of gallium from Bayer process liquor (Indal, Muri) using 7-alkyl-substituted-8-hydroxyquinoline (Kelex-100). Trans. Indian Inst. Met. 51(4), 223225 (1998)
S. Dey, R.P. Bhagat, R.K. Kunwar, D.S. Rao, B. Banerjee, S.C. Maulik, Comparative studies on beneficiation of bauxite samples for application in refractory industry. Met. Mater. Process. 13(1), 18 (2001)