A review of coal demineralization and desulphurization by chemical leaching

Abstract

Coal is a well-known fossil fuel. It was used as a non-renewable energy source for several centuries. Nowadays it is mainly used for electricity generation in power plants or heat generation for industrial and home utilization. There are many types of coal that differ in composition and calorific value, as well as in the amounts of undesired hazard substances produced by combustion. Depending on the coal composition, environmental impact can be reduced by its treatment before combustion. One of the cheap and effective methods is the chemical leaching of coal that reduces sulfur content and the amount of mineral matter (ash). Lowering the ash amount increases the calorific value of coal, reduces its transportation cost, and reduces the negative environmental impact of toxic elements, which are usually present in ash. Another benefit of coal leaching, that results from lowering the sulfur content is reduced emission of toxic gases (SO2 and SO3) during combustion. In order to determine the optimal leaching conditions for the treatment of different types of coal, numerous studies have been done, investigating various chemical reagents, including inorganic and organic acids, alkalis, oxidative reagents, and their combinations [1, 2]. The key parameters that effect leaching efficiency are type and concentration of reagent, reaction temperature, the mass ratio between coal and leaching reagent, coal particle size, and reaction time. The degree of leaching efficiency is measured by the level of demineralization and desulphurization [3]. The current review summarises recent results and further plans for the development of an efficient and environmentally friendly method for the chemical leaching of Serbian sub-bituminous coal.