Mineral Processing
Raheleh Hazrati; Shahram Rostami; Sadegh Marahem
Abstract
The components of low-grade bauxite were 28.4% silica, 34.9% alumina, 16.1% iron oxide as ferric oxide and 11.26% loss on ignition. Due to the high silica content of this type of bauxite, it couldn’t be processed by Bayer method. Therefore, a sintering method with limestone and sodium carbonate ...
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The components of low-grade bauxite were 28.4% silica, 34.9% alumina, 16.1% iron oxide as ferric oxide and 11.26% loss on ignition. Due to the high silica content of this type of bauxite, it couldn’t be processed by Bayer method. Therefore, a sintering method with limestone and sodium carbonate was used for selective extraction of alumina. Experimental design was performed by surface response method (RSM) using central composite design. Selected parameters were temperature, soaking time, mole ratio of sodium oxide to alumina, mole ratio of calcium oxide to silica. The maximum amount of extraction of alumina from low-grade Jajarm bauxite by sintering method was 74.2%, which was obtained in the optimal values of the parameters as follows: A temperature of 1157°C, a soaking time of 35 minutes, a mole ratio of alkaline oxide (K2O + Na2O) of 1.25 and a mole ratio of calcium oxide to silica of 1.99. In 31 run experiments, the mixture of materials powder was transferred to an alumina crucible and heated in a muffle furnace at temperatures and soaking times determined by the experimental design. The sintered material was pulverized. The resulting powder was leached by 150 mL of a boiling alkaline solution (20 g/L NaOH + 20g/L Na2CO3) for 30 minutes at a stirring speed of 300rpm. Extracted aluminum from the leaching stage was analyzed by atomic absorption spectrometry.
Mineral Processing
Reza Khodadadi Bordboland; Asghar Azizi; Mohammad Reza Khani
Abstract
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 ...
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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 36.22% Al2O3, 22.11% SiO2, 20.42% Fe2O3, 3.33% TiO2, and 3.13% 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, Na2O(caustic) concentration, CaO/SiO2 molar ratio, and Na2O/Al2O3 molar ratio. The findings indicated that the extraction rate improved by increasing the sintering temperature and CaO/SiO2 ratio and decreasing the Na2O(caustic) dose and Na2O/Al2O3 ratio. It was also found that the Na2O(caustic) concentration, sintering temperature, and interactive effect of Na2O(caustic) concentration with Na2O/Al2O3 ratio had the greatest influence on the extraction efficiency. The process optimization was conducted applying the desirability function approach, and more than 71% of Al2O3 was extracted at 1150 °C sintering temperature, 2.1 CaO/SiO2 molar ratio, 0.9 Na2O/Al2O3 molar ratio and 30 g/L Na2O(caustic) dose. Ultimately, it was concluded that a lime-soda sintering process at 1150 °C followed by one-step alkaline leaching with Na2O(caustic) at 90 °C could be metallurgically efficient for treating the low-grade (shale) bauxites.
