Abstract
The present study aimed to optimize the calcination process parameters (viz., temperature, time, and particles size) for the extraction of aluminum from Ethiopian kaolinite. The kaolinite calcination was done in the temperature of 600–700°C, time of 120–180 min, and particles size of 106–355 μm. The extraction of aluminum from calcined kaolinite was carried out at fixed acid concentration of 3 M, temperature of 80°C, liquid-to-solid ratio of 12 mL g−1, time of 120 min, and stirring speed of 700 rpm. The chemical composition of kaolinite was determined using XRF. Moreover, kaolinite, metakaolinite, and extracted aluminum were characterized by XRD, TGA, DSC, and FTIR. The XRF result of the kaolinite was mainly silicon oxide (55.76% w/w), aluminum oxide (32.02% w/w), and loss on ignition (11.17% w/w). Calcination of kaolinite produced amorphous metakaolinite due to the dehydroxylation reaction as shown by the FTIR results. Three endothermic peaks and one exothermic peak were detected in the thermal analysis of the kaolinite due to water removal, impurities decomposition, dehydroxylation reaction, and phase change from metakaolinite to spinel, respectively. The extracted aluminum proportionally increased with kaolinite calcination temperature and time. However, the extracted aluminum increased as the particles size reduced. The extracted aluminum was in the form of aluminum chloride hexahydrate and trigonal crystalline structure. The optimum values of the degree of conversion of kaolinite dehydroxylation reaction and extracted aluminum of 0.992 and 71.28% w/w were obtained at the optimum kaolinite calcination temperature of 700°C, time of 180 min, and particles size of 106 μm, respectively.
Highlights
Academic Editor: Eric Guibal e present study aimed to optimize the calcination process parameters for the extraction of aluminum from Ethiopian kaolinite. e kaolinite calcination was done in the temperature of 600–700°C, time of 120–180 min, and particles size of 106–355 μm. e extraction of aluminum from calcined kaolinite was carried out at fixed acid concentration of 3 M, temperature of 80°C, liquid-to-solid ratio of 12 mL g−1, time of 120 min, and stirring speed of 700 rpm. e chemical composition of kaolinite was determined using X-ray fluorescence (XRF)
The extracted aluminum increased as the particles size reduced. e extracted aluminum was in the form of aluminum chloride hexahydrate and trigonal crystalline structure. e optimum values of the degree of conversion of kaolinite dehydroxylation reaction and extracted aluminum of 0.992 and 71.28% w/w were obtained at the optimum kaolinite calcination temperature of 700°C, time of 180 min, and particles size of 106 μm, respectively
E metakaolinite is more active and easier to react with acid than the kaolinite for extraction of aluminum [8]. e calcination kaolinite activated the aluminum oxide layer within the kaolinite structure which could accelerate the extraction of aluminum with acid dissolution [9]. e extraction yield of aluminum enhanced through the formation of metakaolinite via calcination [10]. e extraction of aluminum from metakaolinite could be carried out using mineral acids such as hydrochloric acid, sulfuric acid, and nitric acid [11–13]. e rate of extraction of aluminum from metakaolinite has been fastest with hydrochloric acid and slowest with nitric acid
Summary
Pretreatment and Calcination. e raw kaolinite was collected from Awash Melkassa Aluminum Sulphate and Sulfuric Acid Share Company, Ethiopia. e quarry site of kaolinite is Shakiso, which is located 5o 45′N, 38o 55′E, Southern Ethiopia. e kaolinite pretreatment was conducted using procedures of Mirwan et al [13] with some modifications. e raw kaolinite was soaked in ultrapure water to remove impurities and debris. e kaolinite was dispersed in water, and the insoluble solid residue was discarded. e dispersion was left overnight to separate the wet kaolinite and supernatant liquid. e wet kaolinite was dried with sunlight for 24 h and in the oven for 24 h at 105°C. E raw kaolinite was collected from Awash Melkassa Aluminum Sulphate and Sulfuric Acid Share Company, Ethiopia. E kaolinite pretreatment was conducted using procedures of Mirwan et al [13] with some modifications. E kaolinite was dispersed in water, and the insoluble solid residue was discarded. E dispersion was left overnight to separate the wet kaolinite and supernatant liquid. E extracted aluminum solution was separated from the slurry using centrifuge (PrO-Analytical C2004, United Kingdom) at 2000 rpm for 15 min. 700 120 180 106 355 aluminum were formed in the concentrated solution. E crystals of aluminum were separated from concentrated solution and kept on plastic sheets for 48 h. E partially dried crystals of aluminum were dried in the oven (TD-1315, United Kingdom) at 70°C for 3 h. 700 120 180 106 355 aluminum were formed in the concentrated solution. e crystals of aluminum were separated from concentrated solution and kept on plastic sheets for 48 h. e partially dried crystals of aluminum were dried in the oven (TD-1315, United Kingdom) at 70°C for 3 h. e dried samples were stored in tightly closed plastic bags for further analysis
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