A comparative two-stage, low temperature extraction of silica and alumina from coal fly ash to facilitate acid leaching of rare earth elements

Coal Fly ash (CFA) is an industrial waste but it contains packets of values such as alumina and rare earth elements (REEs) which can be extracted for use. The aluminosilicate phase constitutes a barrier to extraction of REEs from CFA during acid leaching. As a preliminary preparation for extraction of the entrapped REEs, this study examines a comparative two-stage process for low temperature extraction of silica conducted on Nigerian CFA samples. Samples were roasted with NaOH pellets at 100, 200 and 300 oC. The roasted products were subjected to room temperature leaching with the use of NaOH solution for the extraction of silica. Optimum silica extractions of 16.31%, 16.81% and 17.84% were obtained at 6 M, 90minutes, 30 mL/g; 6 M, 90minutes, 30 mL/g; and 3 M, 60minutes, 20 mL/g conditions of base conc, time and liquid-solid ratio for samples roasted at 100, 200 and 300°C respectively. A progressive quantitative silica extraction was observed with temperatures.