DETERMINATION OF RARE-EARTH ELEMENTS IN COAL USING MICROWAVE DIGESTION AND GRADIENT ION CHROMATOGRAPHY

The combined application of microwave digestion, high-performance ion chromatography (HPIC) and on-line sample solution concentration provid es a technique for the routine determination of rare-earth elements (R EE) in coals. Acid dissolution of whole powdered coal samples using mi crowave pressure digestion removes the necessity of dry ashing to elim inate organic carbon, providing considerable time savings and signific antly reducing the risk of sample loss and cross-contamination when sa mples are prepared in batches. HPIC analysis using chelation chemistry and gradient elution enables the separation and determination of 12 o f the 14 naturally occurring REE in coals. The use of on-line sample s olution concentration provides detection limits for individual element s of between 10 and 50 ng g(-1) in the original coal. These are satisf actory for the analysis of low-ash, low-REE, coals, despite the small sample size (0.2 g) employed in this study, which was dictated by the use of medium-pressure digestion vessels. Reproducibility of the techn ique has been determined as generally better than +/- 5% CoV in the an alysis of low-ash coals. REE data produced for coal standard reference materials NBS-1632a, SARM-18, SARM-19 and SARM-20 are generally in go od agreement with published values. Data are also provided for the new low-ash coal standard CLB-1.