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Aluminium ke atileng ka ho fetisisa tšepe elements fumanoa Lefatšeng, kakaretso mabapi 8% ea karolong e ka holimo ea Lefatše. Leha ho le joalo, aluminum as an element is reactive and, ka hona, does not occur naturally – it needs to be refined to produce aluminum metal. Le ka sehloohong a simolla boitsebiso bakeng sa aluminium ho hloekisoa ke bauxite, a lefatše a ka sehloohong khoebo mohloli oa aluminium. Bauxite is a sedimentary rock and consists mostly of the aluminum minerals gibbsite (Al(OH)3), boehmite (mdlody-Alo(OH)), le diaspore (a-Alo(OH)), 'me hangata e kopantsoe le li-oxide tse peli tsa tšepe goethite le hematite, the aluminum clay mineral kaolinite and small amounts of anatase (TiO2) le/kapa ilmenite (FeTiO3).
Bauxite mobung ke ha namela libakeng tse lefatšeng ka bophara, hangata li etsahala libakeng tse chesang tse mongobo kapa tropike. Le hoja mehloli e netefalitsoeng ea bauxite e lebelletsoe ho tšoarella lilemo tse ngata, boleng ba mehloli eo ka moruong accessed e fokotseha. For refiners who are in the business of bauxite processing to make alumina and, eventually, aluminum metal, ena ke ntho e thata ka boleloang bobeli lichelete le tikoloho.
The process of refining metallurgical bauxite into alumina involves the following inputs:
Liphetho tse latelang lia hlahisoa:
Mokhoa o sebelisoang haholo oa lik'hemik'hale oa ho hloekisa bauxite hore e be alumina, tšebetso ea Bayer, e kenyelletsa ho qhaqha Al2O3 ho tsoa lefikeng la bauxite ka soda ea caustic (NaOH) mocheso o phahameng le khatello. The Al2O3 fraction of the bauxite is dissolved into a solution, which is later precipitated out as alumina. Leha ho le joalo, high-grade bauxite contains up to 60% Al2O3, 'me li-depositi tse ngata tsa bauxite tse sebetsang li ka tlaase ho mona, ka linako tse ling e le tlase ka 30-40% Al2O3. Because the desired product is a high-purity Al2O3, le oxides setseng ka bauxite ho (Fe2O3, SiO2, TiO2, Lintho tse phelang) li arotsoe ho Al2O3 'me li hanoa kaha setsi sa ho hloekisa alumina se lula (ARR) kapa seretse se sefubedu. Ka kakaretso, the lower the quality of the bauxite (i.e., lower Al2O3 content), seretse se sefubelu se eketsehileng se hlahisoa ka tone ea sehlahisoa sa alumina. Holim'a moo, even some Al2O3-bearing minerals, haholo-holo kaolinite, hlahisa liphetoho tse sa rateheng-morao nakong tshebetso ho hloekisoa le ho lebisa ho eketseha ha seretse molokong o mong ka o mofubelu, hammoho le ho lahleheloa ke e bitsang chelete e ngata caustic soda lik'hemik'hale, a high 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, hangata e le ph ya 10 - 13. E hlahisoang ka meqolo e kholo lefatšeng ka bophara - latela USGS ho, hakanngoa lefatše ea alumina hlahisoeng ha e ne e le 121 boima ba lithane tse limilione tse ka 2016. Mohlomong sena se ile sa fella ka ho fetang 150 boima ba lithane tse limilione tse seretse khubelu generated nakong eona eo. Ho sa tsotellehe ho etsa lipatlisiso e tsoelang pele, khubelu seretse jwale o maloa litsela tsa ka mokhoa oa thekiso solofetsang ho molemo botjha tšebeliso. It is estimated that very little red mud is beneficially re-used worldwide. Ho ena le hoo, seretse khubelu e pumped ho tswa ho hloekisoang ea alumina ka impoundments polokelo kapa landfills, where it is stored and monitored at a high cost.
Tahlehelo ea theko e phahameng caustic soda (NaOH) 'me ho hlahisoa ha seretse se sefubelu ka bobeli li amana le boleng ba bauxite e sebelisoang ts'ebetsong ea ho hloekisa. Ka kakaretso, e ka tlaase ho Al2O3 content ea bauxite, e kholoanyane molumo oa khubelu seretse hore tla generated, kaha mekhahlelo e seng ea Al2O3 e hanoa e le seretse se sefubelu. Holim'a moo, e phahameng kaolinite kapa silika e sebetsang ka thata ea bauxite, seretse ho feta tse khubelu tla 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. Ka lebaka leo,, both an economic and environmental argument must be made to improve 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. Mokhoa ona o na le melemo e mengata:
Ka kakaretso, sebetsa ommeng le STET kgaoganyo e fana ka menyetla ea ho hlahisa boleng bakeng sa bahlahisi ba bauxite le refiners. Ea pele ho sebetsa pele ho bauxite hloekisoa tla fokotsa ditjeo lik'hemik'hale, fokotsa bophahamo ba modumo ea seretse khubelu generated le fokotsa thulaganyou e o tshwenyang.
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