Jason C. Willett

Preliminary report on the International Energy Agency mode of occurrence inter-laboratory comparison; Phase I, USGS results

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards (or with North American Stratigraphic Code). Any use of trade, product or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Introduction Understanding the mode of occurrence of trace-elements in coal is an important part of predicting element behavior and determining element mobility during coal utilization and storage. A wide range of techniques is currently used to make these determinations. To generate information on modes of occurrence some labortories rely on analysis of density separates, others use various solvents to selectively leach inorganic constituents and yet others use microbeam instruments such as scanning electron microscopes and electron microprobes. No two laboratories use the same approach or rely on the same assumptions. Under these circumstances is it possible to confidently compare the results of different laboratories? To answer this question, the U.S. Geological Survey (USGS) and eight other laboratories* are participating in an international laboratory comparison study of homogenized coal samples. The International Energy agency (IEA) has endorsed this inter-laboratory study and has agreed to publish a summary comparing the results. To date, samples of four coals have been distributed to participating laboratories. Mode of occurrence (chemical speciation) determinations for three of these coals, Gascoigne-Wood #2 (England), Illinois #6 (USA), and Wyee (Australia), are presented in this paper. Results from the 4th coal from Canada will be presented when the data are completed. Information on the rank, ash content and sulfur content of these three samples is given below (Table 1). USGS bulk chemical data and preliminary bulk data from six other participating labs are given in Appendix 1. Because these data are preliminary only the USGS results are identified. We have just begun work on the fourth coal and results are not yet available. As part of this study each of the participating laboratories* are determining trace element modes of occurrence using their own respective techniques. All procedures are unique. Three labs are using leaching procedures, three labs are using density procedures and several labs are using SEM and/or microprobe as their primary or secondary method of determining modes of occurrence. The USGS modes of occurrence data are presented here with comparisons to other results in specific cases. The complete mode of occurrence data set and possibly a statistical comparison of the bulk chemical results will …