Extracting Alumina from a Low-grade (Shale) Bauxite Ore using a Sintering Process with Lime-soda followed by Alkali Leaching

The global growth of aluminum demand with the modernization of our society has led to the interest in developing alternative methods to produce aluminum from non-bauxite and low-grade resources such as shale bauxites. For such reserves, the conventional Bayer process is challenging and is not efficient to extract aluminum, and the sintering process is known to be effective. Thus, this study aimed to scrutinize the technical feasibility of alumina extraction from an Iranian low-grade (shale) bauxite ore containing ۳۶.۲۲% Al۲O۳, ۲۲.۱۱% SiO۲, ۲۰.۴۲% Fe۲O۳, ۳.۳۳% TiO۲, and ۳.۱۳% CaO. In this regard, the sintering process with lime-soda followed by alkaline leaching was adopted to extract alumina, and response surface modeling was employed to assess the important parameters such as the sintering temperature, Na۲O(caustic) concentration, CaO/SiO۲ molar ratio, and Na۲O/Al۲O۳ molar ratio. The findings indicated that the extraction rate improved by increasing the sintering temperature and CaO/SiO۲ ratio and decreasing the Na۲O(caustic) dose and Na۲O/Al۲O۳ ratio. It was also found that the Na۲O(caustic) concentration, sintering temperature, and interactive effect of Na۲O(caustic) concentration with Na۲O/Al۲O۳ ratio had the greatest influence on the extraction efficiency. The process optimization was conducted applying the desirability function approach, and more than ۷۱% of Al۲O۳ was extracted at ۱۱۵۰ °C sintering temperature, ۲.۱ CaO/SiO۲ molar ratio, ۰.۹ Na۲O/Al۲O۳ molar ratio and ۳۰ g/L Na۲O(caustic) dose. Ultimately, it was concluded that a lime-soda sintering process at ۱۱۵۰ °C followed by one-step alkaline leaching with Na۲O(caustic) at ۹۰ °C could be metallurgically efficient for treating the low-grade (shale) bauxites.

کلیدواژه ها:

Low-grade bauxite ، Aluminum leaching ، Sintering ، Dissolution yield ، Optimization