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Rare earth elements (REEs) have been found in coal and coal by-products but occur in their lower contents and inside crystal structures of silica-alumina, leading their extraction challengeable. This study is regarding the pre-treatment of coal by-products, herein coal slurry, prior to the extraction of REEs. The alkali additives (specially sodium carbonate) were applied to pre-treat coal slurry under elevated temperatures for the destruction of crystal structures of silica-alumina in the coal slurry and the exposure of REEs for their further acid-extraction. Studies addressed effects of the alkali additive, mole ratio, calcination temperature, leaching pH, on the leaching efficiency of REEs and the acid consumption. Results indicated that the alkali calcination necessarily and significantly improved the efficiency of the following-up acid extraction of REEs from coal slurry, and the use of supercritical contributed for the pH adjustment and acid saving. The optimal procedure on REEs leaching from coal slurry was found to be sodium carbonate as alkali calcination additive, a molar ratio of coal-slurry/alkali at 1:1, a calcination temperature at 850°C, the supercritical CO 2  and acid leaching at pH = 2, under which Under the optimal conditions, REEs extraction efficiency of all involved coal slurry achieved to be over 90%.

Effective extraction of rare earth elements from coal slurry