DETERMINATION OF PYRITIC SULFUR AND ORGANIC-MATTER CONTENTS IN SPANISH SUBBITUMINOUS COALS BY X-RAY POWER DIFFRACTION

Two analytical methods for the indirect determination of pyritic sulph ur and ash contents in Spanish subbituminous coals by means of X-ray d iffraction (XRD) are described. An indirect analytical method for pyri tic sulphur is used to determine this type of sulphur in high-sulphur coals from the Teruel and Mequinenza mining areas (northeastern Spain) . The analytical method is based on the quantification by means of XRD of the hematite content resulting from the oxidation of iron sulphide s after coal ashing at 750-degrees-C. It has been possible to use this analytical method for the particular coals studied because they do no t contain iron carbonates or organic-fixed iron in appreciable amounts . It can thus be assumed that the hematite in the ash proceeds exclusi vely from the oxidation of iron sulphide. The method of determining th e ash content in coal by means of XRD was devised in order to analyze small amounts of samples from density separations. The small amount of sample available (some fractions lower than 0.5 g) and the need to an alyze various parameters (sulphur, mineral and trace element contents) in the sample did not allow us to determine the inorganic content by ashing. The method permits the total recovery of the sample for subseq uent analyses and the determination of the different mineral phases. T he method devised is based on the quantification of scattering due to the organic matrix in XRD. The organic matrix, as an amorphous matrix, increases the X-ray diffraction background intensity (scattering curv e) by amorphous scattering, to an extent proportional to the organic m atter content. The main advantages of this method is its speedy determ ination (4 min) and the possibility of sample recovery for subsequent analyses.