Effect of elevated temperature and pressure on the leaching characteristics of Indian coals

Abstract

The Indian coal washing circuits are cursed with the availability of high ash coals having poor liberation characteristics as feed material. This result in unacceptably very low product yield (i.e. 10–15%) when aspiring for low ash clean coal (around 8–10%) for efficiently utilising it in iron making process in the form of coke. In this context, a chemical beneficiation route has been explored for demineralising high ash Indian coals. In this work, the effect of aqueous alkali leaching followed by acid washing on the removal of mineral matter from two different captive coals of Tata Steel at elevated temperature and pressure have been explored. The research study revealed that it is possible to reduce the ash content up to 70% by this method. The effect of process conditions such as alkali concentration, temperature and pressure upon the demineralisation kinetics have been investigated. The alkali content of the product coal does not increase whereas the silica and alumina content reduces by nearly 51.3% and 58.8% respectively. Significant reduction in the phosphorus content is observed after the acid treatment. The process does not significantly affect the crucible swelling number index for coking property of coal.