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Korean Journal of Metals and Materials > Volume 56(1); 2018 > Article
Korean Journal of Metals and Materials 2018;56(1): 49-58. doi: https://doi.org/10.3365/KJMM.2018.56.1.49
Recovery of Fine Aluminum Hydroxide with High Whiteness Index from Low Quality Bauxite Using Caustic Roasting and Water Leaching
Su Jin Kim1, Jeong Il Lee2, Kyu Sung Han1, So Yeong Byun1, Tam Tran1, Myong Jun Kim1
1Department of Energy & Resources Engineering, Chonnam National University, Gwangju 61186, Republic of Korea
2Water Quality Analysis Division, Jeollanam-do Institute of Health and Environment, Muan 58568, Republic of Korea
Correspondence  Myong Jun Kim ,Tel: +82-62-530-0462, Email: junkim@jnu.ac.kr
Received: 11 May 2017;  Accepted: 29 September 2017.  Published online: 1 January 2018.
ABSTRACT
A bauxite of low quality containing 6.75% reactive silica and 37.4% Al2O3 as gibbsite was roasted with additives including NaOH (caustic/total alumina molar ratio of 2-4:1) and CaO (CaO/total SiO2 molar ratio of 0.5-3:1) at 300-1000 oC, producing calcines containing sodium aluminate (Na2O.Al2O3), silicates and hematite. Optimum conditions included roasting at 350-400 oC with CaO added at a CaO/total SiO2 molar ratio of 1:1 for 2-3 h. Dissolving the calcine in water at 90 oC produced a sodium aluminate liquor from which aluminum hydroxide (Al2O3.3H2O – alumina trihydrate or ATH) was precipitated. The addition of CaO reduced the silica extraction to <15% at optimum conditions, whereas the total organic carbon(TOC) was ~200 mg/L as carbon in all cases. Losses of alumina and caustic were experienced, as different phases of Al-Ca- Si or Na-Ca-Al-Si minerals were formed during roasting and/or leaching. The extracted alumina in the leached solution were precipitated at 60 oC for 20 h to produce a fine aluminum hydroxide having D50 of 1.9-2.8 μm with a whiteness index of 96.8-97.5, better than commercially available products.
Keywords: fine aluminium hydroxide, high silica, bauxite, caustic roasting, high whiteness
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