New Mexico Geological Society Annual Spring Meeting — Abstracts

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The goal of this research is to identify a procedure suitable for extraction of aluminum oxide, (Al₂O₃) from abundant New Mexico resources. In the interest of economic and environmental viability, the resources of interest include those from prospective, existing or abandoned mines sites.

The method used for this is a variation of the Seailles-Dyckeroff process (also known as the lime-sinter-process), which is more versatile than the Bayer process used commercially as it can remove alumina from any aluminum containing source, whereas the Bayer Process can only extract alumina from low-silica bauxites. [1] The lime-sinter process can extract alumina from feldspars, clay, shale, coal clinkers, coal, and waste products from other processes (such as the Red Mud left behind in the Bayer Process). The reason for this versatility stems from the lime-sinter step of the process where, after the ore is crushed, it is combined with lime (CaCO₃) and pressed into pellets. The pellets are then baked at 1360°C for an hour before cooling overnight in the furnace. This causes a phase change and disintegration into a fine powder. Aluminate ions (^–Al(OH)₄) are then leached using soda ash (Na₂CO₃). The aqueous slurry is filtered to remove calcium silicates, leaving behind a solution of sodium aluminate (NaAl(OH)₄) which is then pumped with CO₂ gas to reduce the sodium aluminate and transform it into gibbsite (Al(OH)₃) and sodium oxide (NaO). [2] The gibbsite precipitates out of the solution and is filtered out once the pH lowers from pH 14 to pH 7.5. [3] The precipitate is then dried washed with glacial acetic acid (CH₃COOH) before being heated to 1200°C in order to convert to aluminum oxide. Preliminary research has been carried out on food-grade kaolinite (a fairly abundant mineral with high aluminum content) with promising results. Early experiments without the acid wash step produced beta-alumina upon 1200°C calcination. Later experiments after the addition of the acid wash step resulted in products shown to be α-alumina with corundum crystal structure. The next stages of this research will be optimization of the process for coal, coal clinkers and clay from samples gathered around New Mexico, but it seems like a good replacement procedure has been found.

References:

1. [1] E.P. Flint, W.F. Clarke, E.S. Newman, L. Shartsis, D.L. Bishop, and L.S. Wells, Extraction of alumina from clays and high.silica bauxites. Part of the Journal of Research of the National Bureau of Standards, 36(RP1691):68–106, 1946.
2. [2] J.C. Seailles and W.R.G. Dyckerhoff, 1941. RECOVERY OF ALUMINA
3. [3] N.-K. Park, H.-Y. Choi, D.-H. Kim, T.J. Lee, M. Kang, W.G. Lee, and J.W. Park, Purification of al(oh)3 synthesized by bayer process for preparation of high
   purity alumina as sapphire raw material. Journal of Crystal Growth, 373:88–91, 2013.