Investigation of the evaluation of diasporic bauxite from İslahiye region in alumina production

In this study, the effect of mechanical activation and Ca(OH)2 additive on alumina production by microwave leaching from diasporic bauxite in Gaziantep – Islahiye region and dehydroxylation kinetics of diasporic bauxite by non-isothermal methods were investigated. According to XRF results of the diasporic bauxite ore, it has been determined that it contains 50.63% Al2O3, 13.87% Fe2O3, 14.52% SiO2, 7.64% TiO2 and 12.75% heating loss. According to the XRD analysis of the ore, diasporite (AlOOH), hematite (Fe2O3), quartz (SiO2), anatase (TiO2), muscovite (KAl2Si3AlO10(OH)2) and kaolinite (Al2O32SiO22H2O) were found in the ore. The effects of the mechanical activation on the structure of diasporic bauxite were investigated and in these studies, in order to see the effect of ball/sample ratio in mechanical activation, in the activation process performed at 15, 25, 35 and 45 ratios for 30 minutes, the degrees of amorphization were found as 24.6%, 42.3%, 53.1% and 59.7%, respectively. In the studies performed at 60 minute, the degrees of amoerphization were calculated as 43.5%, 58.8%, 71.4% and 79.6& respectively. The optimal ball/sample ratio was found to be 25. It was observed that the structure of diasporic bauxite became more amourphous in studies carried out for 60 minutes. In order to see the effects of mechanical activation time, mechanical activation was performed at 25 ball/sample ratio for 15, 30, 60, 90 and 120 minutes and the degrees of amorphization in the structure were calculated as 35.16%, 43,41%, 64.33%, 70.44% and 72.05% respectively. It has been determined that the optimal time in the mechanical activation process is 60 minutes. The degree of amorphization increased significantly up to 60 minutes, and the rate of increase in activation performed for longer periods of time decreased. While the average particle size (D50) was 36.6 µm and the specific surface area was 5.81 m2/g in the non-activated ore, these values were determined as 19.5 µm and 54.36 m2/g after 30 minutes of mechanical activation. After 60 minutes of mechanical activation, the average particle size was 16.70 µm and the specific surface area was 63.18 m2/g. Average particle size slightly increased due to agglomeration in mechanical activation process longer than 60 minutes. It has been determined that the bond structure of diasporic bauxite was weakened due to the reasons such as loss of crystallinity, microtensions, amorphization, disappearence or tendency of the peaks to disappear after the mechanical activation observed by FT-IR analysis. In the thermal analysis of diasporic bauxite, it was observed that dehydroxylation reaction of the non-activated diasporic bauxite occurred at 503°C. the activated ore for 30 minutes dehydroxylated at 471°C and this temperature decreased to 464°C for 60 minute activated ore. As a result of the thermal analysis, it was determined that the non-activated diasporic bauxite was decomposed after 400°C, the weight loss rate increased significantly after mechanical activationand a significant weight loss occurred from room temperature. The non-isothermal dehydroxylation kinetics of diasporic bauxite was carried out using the non-isothermal methods of Kissenger, Boswell and Ozawa. The thermal analysis data was obtained at different heating rates (5 – 10 – 15 – 20 °C/minute). As a result kinetic of study, the activation energy required for the dehydroxylation of non-activated diasporic bauxite was in the range of 231 – 239 kJ/mol. The activation energy for the dehydroxylation of the diasporic bauxite activated for 60 minutes was determined to be 81,7 kJ/mol at the beginning of the reaction because of amorphization in the structure. This value was determined as 141,6 kJ/mol at α=0.5 (half of reaction) and then increased to 226,6 kJ/mol at α=0.7 because of the remaining diasporite in the structure without amorphization. In microwave assisted leaching studies with NaOH, the parameters such as Ca(OH)2 addition, liquid/solid ratio, microwave power and leaching time were investigated for both non-activated diasporic bauxite and 60 minute activated diasporic bauxite. Microwave assisted leaching studies without Ca(OH)2 addition were carried out with 1000 W microwave power and 20 minutes of leaching time as constant, with liquid/solid ratios of 10, 20, 30 and 40. Depending on the solid/liquid ratios, Al% yields remained in the range of 8 – 10% for the non-activated diasporic bauxite, while this yield was in the range of 28 – 39% for the mechanically activated diasporic bauxite. The most suitable liquid/solid ratio was found to be as 20 in these studies. Microwave assisted leaching processes with Ca(OH)2 addition were carried out at 1000 W microwave power and 20 minutes for different liquid/solid ratios (10, 20, 30 and 40). Ca(OH)2 addition had a positive effect on the leaching yield. While Al% yield was 39.62% for the non-activated diasporic bauxite, this value was 64.27% for 60 minute activated diasporic bauxite. When the effect of microwave power (800, 1000, 1200 and 1400 W) on Al% yield was examined by keeping the liquid/solid ratio of 20 and 20 minutes of leaching time as constants in the microwave assisted leaching with Ca(OH)2 addition, it was seen that the most appropriate microwave power was 1200 W. While the Al% yield was 43.65% for non-activated diasporic bauxite at this microwave power, this value was determined as 71.85% for 60 min activated diasporic bauxite. There was not much change in yield at 1400 W of microwave power. When the effect of leaching time (10, 20, 30 and 40 minutes) on the Al% yield was examined by keeping the liquid/solid ratio of 20 and 1200 W of microwave power as constant in microwave assisted leaching with Ca(OH)2 addition. The leaching efficiency was significantly increased up to 30 minutes. However, it was observed that the Al% yield did not change over a longer period. In the 30 minutes of leaching process, the Al% yield was 48.56% for non-activated diasporic bauxite while this value was 79.14% for 60 minute activated diasporic bauxite. In the microwave assisted leaching of diasporic bauxite, both the mechanical activation of the ore as pretreatment and the Ca(OH)2 addition had a very significantly positive effect on the aluminium dissolution from diasporic bauxite. Aluminium hydroxide was precipitated from the solution obtained after the leaching studies by pH adjustment and pure α – Al2O3 was produced by calcining the sample at 900°C for 3 hours. It was revealed that the obtained product is pure α – Al2O3 by both XRD analysis and SEM-EDS analysis. According to the results obtained in this study, it was seen that an acceptable percent of alumina could be obtained by microwave leaching in atmospheric conditions after mechanical activation and Ca(OH)2 addition from diasporic bauxite in Islahiye region.