A new approach for the combined chemical and mineral classification of the inorganic matter in coal. 1. Chemical and mineral classification systems

This work introduces and evaluates a new approach for the combined chemical and mineral classification of the inorganic matter in coal. Thirty-seven coal samples from Australia, Bulgaria, USA, Japan, Canada, South Africa, China, Spain, and Ukraine, which differ considerably in their geology, rank, age, ash yield, chemistry and mineralogy, were used to establish the classifications. The chemical classification system was organized according to the contents and significant positive or negative correlations of ash-forming elements in coal ashes using three composition-based criteria, namely: (1) sum of Si, Al, K, and Ti oxides; (2) sum of Ca, Mg, S, and Na oxides; and (3) Fe oxide. This approach resulted in four chemical coal ash types (sialic, calsialic, ferrisialic, and ferricalsialic) further divided into seven subtypes (with high, medium and low acid tendencies) based on the sum of Si, Al, K, and Ti oxides. The more important mineral classification system was organized according to the contents, genesis, and behaviour of mineral classes and species in coals also using three composition-based criteria, namely: (1) silicates + oxyhydroxides; (2) carbonates; and (3) sulphides + sulphates + phosphates. This approach resulted in four mineral coal types (silicate, silicate–carbonate, silicate–sulphide, and silicate–sulphide–carbonate or mixed) further divided into seven subtypes (with high, medium and low detrital tendencies) based on the sum of silicates and oxyhydroxides. The chemical and mineral coal types and subtypes are characterized and relationships and distinctions between them also are described herein. The benefit of this new classification approach is the use of significant correlations and actual element associations, and well-defined and genetically described mineral classes and species in coal. Potential applications of the classification schemes are described in part 2 of the present work.