Alumina Extraction by Lime-soda Sinter Process from Low-grade Bauxite Soil of Semirom Mine

As the mass ratio of alumina to silica (A/S ratio) in bauxite decreases, the cost of alumina production by the Bayer process sharply increases. With the increasingly fierce competition in the alumina industry and the gradual reduction in bauxite grade, when the A/S ratio drops to ۳-۴, the Bayer process is challenging to meet the market competition and production requirements. In such cases, the alumina production by sintering method has a vast development prospect and application potential for low-grade bauxite ores. The low A/S ratio and the high iron oxide content are the difficulties in the alumina production by the sintering process. This work adopts the lime-soda sinter process for extracting alumina from bauxite samples (A/S ratio = ۱.۳۴ and ۲۰.۸۰% Fe۲O۳) of the Semirom mine in Iran. The effects of sintering parameters are investigated. The maximum alumina extraction (۸۸%) was obtained by a CaO/SiO۲ molar ratio of ۱.۲, Na۲O/Al۲O۳ molar ratio of ۰.۹, and sintering temperature at ۱۲۵۰ °C for ۸۰ min. Also ۸۳% of alumina is extracted by decreasing the N/A ratio to ۰.۶۶, to decrease the sodium carbonate consumption for a more economical process. The sintered materials are leached with sodium carbonate solution, and aluminum hydroxide [Al(OH)۳] is precipitated. Finally, pure alumina (Al۲O۳) is obtained with a purity of ۹۸ % after calcination at ۱۲۰۰ °C for ۲ hours.

Keywords:

Bauxite , Kaolinite , Alumina , Lime-Soda Sinter process , Semirom Mine