Recovery of raw materials containing aluminium
Practically the only process for extracting aluminium used today is the so-called Bayer-process. In this process bauxiteis disintegrated under pressure using sodium hydroxide solution at 180°C. Here the aluminium selectively precipitates as Na[Al(OH)4], while the iron is separated as oxide-hydrate (red sludge) by means of filtration. Due to the fine distribution of the precipitant, the filtration is often plagued by considerable technical problems. The aluminium fraction is brought to crystallisation and then converted into aluminium oxide at around 1200°C . The silicon dioxide from the bauxite converts into sodium-aluminium silicate in wet extraction, which precipitates together with red sludge. The formation of these silicates is then associated with losses of aluminium, which naturally increase with higher concentrations of SiO2 in the bauxite.For this reason there is limited applicability for the classical Bayer-process, which has been constantly optimised over the decades, stemming from the composition of the initial materials.
MME Engineering has know-how concerning alternative routes for extracting aluminium out from primary or secondary raw materials with high proportions of silicate and/or high iron concentrations. With these procedures it is possible specifically to process raw materials with low concentrations of aluminium. Simultaneous separation of iron and aluminium is the key point in this procedure.
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