Demineralization of high ash coal fines of Indian origin using Mahua oil

Abstract

The cost of oil is perhaps the biggest prohibitive aspect of the oil agglomeration process. Furthermore, the high ash low grade coals of India are more difficult to demineralize owing to their unfavourable hydrophilic surface chemistry. The objective of our present study is to use an indigenous and underutilized oil derived from Mahua seeds as a potential bridging liquid for oil agglomeration of low grade coal from Kaniha (Odisha, India) with 35% ash. Based on experimental results, Mahua oil demonstrably proved efficient in demineralization by 45–50% at lower oil concentrations (10–15 wt%), devoid of surfactants. Wet grinding of the coal using a vibratory cup mill was an essential pre-treatment step. A detailed investigation of all the crucial process parameters was performed through variation of pH, oil dosages, solid to liquid ratio and agitation conditions. The results obtained were further validated by detailed characterization of both raw and clean coal using zeta potential, FTIR, SEM studies and petrography. FTIR and petrographic studies validated the inherent and surface hydrophilicity of Kaniha coal. Zeta potential studies clearly showed an increase in surface potential around neutral pΗ which was found to be optimum for oil agglomeration. SEM results conclusively supported the formation of porous large size agglomerates. To our knowledge, ours is the first thorough examination of agglomeration potential of Mahua oil, which is an industrially underutilized product, thus supporting the aim of waste utilization and cleaner fuel production. • Crude Mahua oil as bridging liquid for oil agglomeration of high ash low grade Indian coal (35% ash) has been investigated. • Lower dosage (15 wt%) of oil under neutral conditions gave satisfactory results. • Wet grinding in a vibratory cup mill has been implicated to be a crucial pre-treatment step. • Demineralization by 45–50% was observed. • No pre-conditioning step of surfactant was included.