Abstract
The extraction of Al from Inner Mongolia (China) fly ash by HCl leaching produced a kind of solid waste called red mud (CRM). This red mud contained a great deal of gallium (Ga2O3, 0.305 wt%) and thus it was a very valuable Ga resource. In this work, an easy hydrothermal alkaline leaching method was developed to extract Ga from CRM. This method mainly solved the separation of Ga and Fe, because they existed in CRM in the form of Ga(OH)3 and Fe(OH)3, and the Fe(OH)3 in CRM had a strong coating effect on Ga(OH)3. In this method, Fe(OH)3 was converted to Fe2O3 in hydrothermal environment with small specific surface area, which weakened the coating for Ga(OH)3 and accelerated the leaching reaction between Ga(OH)3 and NaOH. The influencing factors on the leaching rate of Ga were discussed and the optimal Ga leaching conditions were determined as NaOH concentration of 20 wt%, leaching temperature of 120 °C, leaching time of 12 h, filling degree of 50%, reactor rotating state, and liquid-to-solid ratio of 5 mL/g. The leaching rate of 91.4% was obtained for Ga from CRM at the optimal conditions and the Ga2O3 concentration in leaching solution reached 73.44 mg/L. Fe was not detected in leaching solution using hydrothermal alkaline leaching method and the main component of the leaching residue was α-Fe2O3 with small (average size 3.62 μm) and uniform particle size.
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