The surface area of coal particles

Abstract

The nature of coal makes it difficult to define the boundary separating the ‘interior’ and ‘exterior’ surfaces of coal and therefore the meaning of ‘coal particle surface area’ is controversial. The coal industry standard for reporting coal surface area is based on CO 2 gas adsorption near room temperature but the relevance of such data to reactions of coal powder slurried in aqueous solution (e.g. as in coal flotation, oxidation of coal in aqueous media, etc.) is questionable. In this, paper a comparison is made of different surface area measurement methods including: particle sizing, photoextinction, methylene blue dye adsorption and gas adsorption (both noble gas and CO 2). The intercomparison of these results is dependent on coal rank and shows that for high rank coal, dye adsorption can be used reliably as a simple measure of coal surface area available to aqueous solutions.