Influence of Chemical Leaching on Rheology and Ash Reduction of Indian Coal

The quality and calorific value of Indian coal are very low. The objective of the present study was to reduce the ash content and to produce ultraclean coal (UCC). The low-ash-content coal was then used to prepare a coal-oil slurry. The coal was demineralized with a dual-acid leaching process using hydrofluoric acid (HF) followed by nitric acid (HNO3). The leaching concentration was varied from 10-40% (by volume). After chemical leaching, the ash content was reduced from 38.5 to 0.9% (by weight) in the ultraclean coal. The coal-oil slurry was also prepared from treated coal with different concentrations of chemicals. The rheology of the untreated coal-oil slurry and ultraclean coal-oil slurry was investigated using a RheolabQC rheometer. The solid concentration of the coal-oil slurry was taken in the range of 20-40% (by weight). The coal-oil slurry exhibited shear thinning behavior. The SEM micrograph results revealed that some non-porous materials that were present in the untreated coal were removed after chemical leaching. The rheology data also showed that the apparent viscosity of the coal-oil slurry was greatly influenced by ash content.