Enhanced recycling and utilization of mullite from coal fly ash with a flotation and metallurgy process

The recycling and utilization of mullite in coal fly ash (CFA) gives rise to environmental and economic profits. The optimal experimental conditions for enhanced recycling of mullite with a flotation and metallurgy process are studied by factorial designs, and further analyzed by thermodynamic and dynamics calculations, and XRD/SEM characterizations. The unburned carbon is firstly removed from the CFA assisted with effective humic acid surfactant in the froth flotation step. The maximum removal rate of carbon is 93.20 +/- 0.05%. Then the digesting of glass phase in carbon-free product with mixed acid solutions (HF: H2SO4 = 3:1) is employed in the metallurgy step. The influencing intensity of digesting factor on glass phase decreases in order of acid concentration, agitation intensity, reaction time, reaction temperature. The digesting kinetics of glass phase in mixed acid solution is belonging to diffusion controlled reaction model. The maximum digesting rate of glass phase can be 97.40 +/- 0.16%. The mineralogical phase of the digested residue is mainly mullite. The performance of the refractory obtained from the water-cleaned mullite-enriched product meets the production requirements of refractory materials. This potential process would provide an effective approach for the separation and recycling of valuable components from CFA in further industry applications. (C) 2018 Elsevier Ltd. All rights reserved.