Demineralization of high ash non-coking coal fines of Indian origin using Castor oil: Implications of wet milling

The high-ash low-grade coals of Indian origin are relatively more challenging to demineralize due to their unfavorable hydrophilic surface chemistry. Herein, we report castor oil as a potential bridging liquid, which efficiently agglomerated high-ash low-grade coals by 55-60% at lower concentration (10 wt%) compared to literature (20-25 wt%), without inclusion of surfactants. A blend of castor oil and turpentine oil proved further beneficial. Wet milling of coal was a crucial prerequisite for efficient agglomeration. Three low-grade coals, Bhubaneshwari (35.8% ash), Kaniha (35% ash), and Hingula (26% ash), were beneficiated in the present study. A detailed analysis of process parameters validated with structural characterization using FTIR, Petrography, zeta potential, and SEM analysis was performed. The chemistry between ricinoleic acid in castor oil with that of surface functionality of coal is speculated to be the reason behind the obtained agglomeration results. Castor oil, being non-edible, bio-based, non-toxic, and non-polluting in nature, provides a greener alternative to mineral oils toward the production of clean fuel.