Application of diffuse reflectance spectroscopy for quick laboratory assessment of Estonian oil shale quality

Diffuse reflectance spectroscopy in near infrared region was used as a fast laboratory method for quantitative assessment of the calorific value and the moisture content of Estonian oil shale. Samples of different caloricity were collected from Narva opencast mine and from beneficiation plant of Estonia underground mine, Estonia. The set of crushed oil shale samples, which moisture content was varied were tested by the help of a commercial multipurpose analyser, where Fourier-transform spectrometer recorded spectra in near infrared region and the software used partial least squares regression method. Results were related to the values of caloricity and moisture content, obtained by the bomb calorimeter and weighing methods, respectively. Bands characterizing organic and inorganic parts of the samples as well as the presence of the free water were ascertained by the infrared spectroscopy. Using the software provided by the analyser, the calorific value and the moisture content of samples were predicted. The prediction error of the lower caloricity was 1 MJ[kg.sup.1] and prediction error of the weight percent of the moisture content was 1.35%. The comparison between achieved results and the values obtained from earlier laser-induced breakdown spectroscopy (LIBS) measurements shows that in laboratory conditions more precise prediction can be made by diffuse reflectance measurements. Further improvement of the prediction accuracy could be achieved by modified software which considers observed nonlinear effects in spectra. Key words: crushed oil shale, diffuse reflectance spectroscopy in near infrared region, assessment of calorific value and moisture content.