Aluminum (Al) extraction from boxide ore with two stage leach

There are various minerals in the world from which aluminum can be obtained, but the most common raw material is bauxite. Bauxite is a mineral composed of a mixture of many minerals, especially aluminum oxide. If there is more than 50% alumina in the bauxite ore, it is considered as high quality. Aluminum production from bauxite is based on hydrometallurgical techniques (Bayer Process). The process involves leaching of bauxite with NaOH in a pressurized reactor system. First, aluminum hydroxide crystals are obtained from leaching solution and it feeds to electrolytic reduction cells in order to produce aluminum from Al2O3 obtained after filtration-calcined process steps. However, there are some problems occur with time in the Bayer process such as excessive red sludge formation during aluminum production, environmental risk, need of large storage areas, excessive consumption of low-modulus ores and low leaching times in multiple reactor systems. In this study, extraction of metals from bauxite which supplied from Seydişehir Alüminyum I.C was carried out with two step leaching process. In the first stage leaching study, bauxite ore was leached under atmospheric conditions in the presence of oxalic acid and leaching parameters were optimized. In the first stage leaching study, it can be said that a selective leaching process is performed based on using oxalic acid as organic acid that have selective solubility on iron, however, it is not affect aluminum in bauxite structure that has refractory properties. Optimum leaching conditions in the first stage leaching process were determined as 110 g / l H2C2O4, leaching temperature of 85 °C, 120 min leaching time, 25: 1 ml/g liquid-solid ratio and stirring speed of 400 rpm. Leaching efficiencies under optimum leaching conditions were determined as 2.82% Al, 82.7% Fe and 55.54% Ti. The first stage leach residue was characterized and it was used to recover aluminum in leaching operations on the second stage leaching. As a result of the chemical analysis of the leach residue of the first stage, it was determined to be 71.61% Al2O3, 1.71% Fe2O3, 2.82% TiO2 and 8.42% SiO2. In the second stage leaching studies, the best results were obtained in experimental studies conducted in the presence of NaOH in a pressurized reactor system. In the second stage leaching, optimum leaching conditions were determined as 3-5 M NaOH, 165 °C of leaching temperature, 10-60 min of leaching time, 4.03 bar pressure, 400 rpm of mixing speed and 25 ml/g of liquid-solid ratio. Under these conditions, while approximately 70% Al extraction was obtained, iron remained in solid. Keywords: Bauxite, hydrometallurgy, oxalic acid leaching, pressure leaching, aluminum, Bayer process, selective extraction.