Interpreting crystallographic and microcrystalline structural effect for demineralization of low-grade thermal coal in multi-stage chemical leaching: A cleaner combustion approach

Chemical leaching is one of the most efficient methods for improving low-grade coal due to its ability to remove both inorganic and organic minerals economically. This study examined the qualitative demineralisation using the XRD and FTIR analyses. Moreover, microcrystalline analysis was investigated by analysing the Micro-Raman spectra, and ash composition was analysed using XRF Spectroscopy analysis for coal samples. Furthermore, a correlation was established between a Raman parameter (AD/AG) and a crystallite parameter (Lc). The demineralisation mechanism was postulated in light of the findings to explain how significant impurities (SiO2 and Al2O3) with iron-bearing elements (Fe2O3 and FeS2) were curtailed during multi-stage leaching. The maximum deashing and demineralisation were obtained by treatment with 40% (w/v), i.e. 10 M NaOH, followed by HCl with HNO3 solution in a 3:1 ratio, with an average particle size of 180 μm. 79% ash reduction and 48% enhancement in GCV were achieved compared to raw coal. [Display omitted] •Multi-stage leaching with alkali and acid treatment.•Ash removal and demineralization enhanced by increasing alkali concentration.•HCl with HNO3 showed better ash removal and demineralization than sole HCl.•Structural defects enhanced in multi-stage leaching with increasing AD/AG & FWHM.•Maximum 79% deashing with 48% GCV upliftment achieved after multi-stage leaching.