Chemical leaching of coals would be required to produce cleaner coals for some special applications where physical beneficiation may not be effective enough. This would also help in recovering Li and rare earth metals besides in the sequestration of CO₂. About 20 Indian coals having complexly distributed moderate to high ash contents were sequentially treated with various alkali–acid such as NaOH-HCl, HF, HCl, HCl-HF, and NaOH-HCl-HF leaching. This aimed to establish and design the best stepwise sequential process for the highest degree of demineralisation through a chemical leaching process. Kinetics and process intensification studies were carried out. More than 80% demineralisation of Madhaipur and Neemcha coals was observed using the best sequential treatment designed presently. The repeated stepwise treatment of the alkali and the acid was also studied, which was found to significantly enhance the degree of demineralisation of coals. The integrated process of alkali–acid leaching followed by solvent extraction (Organo-refining) and vice versa of the treated coal was also studied for producing cleaner coals.

对于一些物理选矿可能不够有效的特殊应用，需要对煤炭进行化学浸出来生产更清洁的煤炭。除了封存CO ₂之外，这还有助于回收Li和稀土金属。对约 20 种分布复杂的中高灰分的印度煤炭进行了不同的碱酸浸出，如 NaOH-HCl、HF、HCl、HCl-HF 和 NaOH-HCl-HF 浸出。其目的是建立和设计最佳的逐步顺序工艺，通过化学浸出工艺实现最高程度的脱矿质。进行了动力学和过程强化研究。使用目前设计的最佳序贯处理，观察到 Madhaipur 和 Neemcha 煤的脱盐率超过 80%。还研究了碱和酸的重复逐步处理，发现这可以显着提高煤的脱矿程度。还研究了碱酸浸出、溶剂萃取（有机精炼）以及处理过的煤的反之亦然的集成工艺，以生产更清洁的煤炭。