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 provides a technique for the routine determination of rare-earth elements (REE) in coals. Acid dissolution of whole powdered coal samples using microwave pressure digestion removes the necessity of dry ashing to eliminate organic carbon, providing considerable time savings and significantly reducing the risk of sample loss and cross-contamination when samples are prepared in batches. HPIC analysis using chelation chemistry and gradient elution enables the separation and determination of 12 of the 14 naturally occurring REE in coals. The use of on-line sample solution concentration provides detection limits for individual elements of between 10 and 50 ng g^-1 in the original coal. These are satisfactory 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 technique has been determined as generally better than ±5% CoV in the analysis of low-ash coals. REE data produced for coal standard reference materials NBS-1632a, SARM-18, SARM-19 and SARM-20 are generally in good agreement with published values. Data are also provided for the new lowash coal standard CLB-1.