Valorization of bauxite residue is of great importance for sustainable production of aluminium, and the research in this field is continued in this bachelor thesis. Hydrogen reduction of iron in a mixture of bauxite residue and limestone was studied based on experimental work. In addition, the leaching of the reduced samples was done to research the extraction of aluminium trihydroxide and further acquisition of alumina. The research was done with the intention of further valorization of bauxite residue, eliminating the waste of the aluminium industry. Hydrogen was purposefully used as reductant to reduce the carbon emissions of the process.
To enable reduction of the mixture, it was pelletized and sintered. The sintered pellets were then reduced at three different temperatures (1000, 1100 and 1200°C) and four durations (0.5, 1.5, 2 and 2.5 h). The variation of temperature and time was done to investigate their influence on the production of metallic iron, both separately and cooperatively, to determine the optimal reduction conditions. Comparison of the reduction experiments indicate that temperature is the most important parameter considering the overall yield of metallic iron, even though time remains important, especially at higher temperatures.
Various analytical methods and instruments were used to characterise the samples. With use of XRF, each sample’s contents were quantified prior to reduction. Consequently, the reduced samples were studied with SEM and XRD to inspect the morphology and composition. The leached samples were analysed with XRD for determining composition, in addition to qualitative analysis through ICP-MS.
The results from the reduction experiments revealed that reduction 4 (1000°C, 2.5 h) was the most beneficial for reducing iron, with a yield of 82.9%. When considering the extraction of aluminium after leaching, reduction 2 (1000°C, 1 h) yielded the most with 86.6%. When combining the results from the reduction and leaching experiments, it was concluded that reduction 4 was the most beneficial, giving the greatest combined yield of both iron (82.9%) and aluminium (82.0%), granting the best overall valorization of bauxite residue.