Quantification of mineral matter in the Argonne Premium Coals using interactive Rietveld-based X-ray diffraction

The mineral matter in the eight reference North American coal samples of th e Argonne Premium Coal series has been investigated on a quantitative basis using X-ray diffraction (XRD) techniques. X-ray diffraction data obtained from electronic low-temperature (oxygen-plasma) ash (LTA) residues, from as hes produced by heating the coals in air at 370 degreesC, and also from the raw coals themselves, were evaluated using an interactive data processing system (SIROQUANT (TM)) based on Rietveld interpretation methods. The resul ts from the three types of material (LTA, 370 degreesC ash and raw coal) we re compared for each sample. This allowed the components present in the raw coals in crystalline form to be recognised separately from mineral artifac ts produced, particularly in the low-rank coals, from interaction of organi cally associated elements (Ca, S, etc.) during the two ashing processes. After the allowance for the production of any artifacts, the quantitative m ineral assemblages identified from XRD of the raw coals were found to be co nsistent, even for coals having a relatively low ash percentage (around 5%) , with the results obtained from the respective mineral concentrates prepar ed by the ashing methods. The effects of heating the coal to 370 degreesC c ould also be distinguished, relative to the raw coal or the LTA, through ch anges in components such as pyrite and the clay minerals. Although some areas of uncertainty exist, particularly with magnesium in th e low-rank coals, the calculated chemical compositions of the coal ash deri ved from the mineral mixtures identified for each coal were also found to b e consistent with the results of direct chemical analysis of the respective coal ash materials. (C) 2001 Elsevier Science B.V. All rights reserved.