Synthetic Sulphur Calibrant Method

Stage 2 (August 2014)

In this project extension, the method for determination of sulphur in coal using a synthetic calibrant was further developed and validated for suitability in an ILS.  The current SA (Standards Australia) method AS 1038.6.3.3 for Total Sulfur was modified to include this use of this synthetic calibrant for instrument calibration.

Results received from all 17 labs involved in the ILS were evaluated statistically, with significant consideration given to the accuracy and precision data so that a decision can be made regarding progression of the method for incorporation into the Australian standard AS1038.6.3.3.  As part of the evaluation of accuracy and precision, values for these key indicators from the SA and ISO methods were used to benchmark the ILS results.

During closer examination of the ILS results, it was observed that the determined sulphur values from several labs were close to the true values for all samples, which indicated that the method was sound, but that more research is needed to identify the reasons as to why the results were not consistent across all 17 labs.

A further statistical analysis was performed on results from 4 selected labs and a statistical evaluation of this data set indicated that results were sufficiently accurate to justify further work on the method, which should lead to progression to an Australian standard method.

Stage 1 (January 2012)

Sulphur is a key parameter in the trading of coal and it is therefore most important that accurate determination of sulphur levels is maintained into the future. This is particularly so as new rapid instrumental methods of determination continue to take over from classical methods of analysis. Calibration of these analysers is currently performed using certified reference coals, but there is growing concern over the accuracy of their sulphur values, due to transfer of small analysis errors (systematic errors) from old to new reference coals. It should be noted that many of these instrumental techniques including those used for the determination of sulphur are comparators and the accuracy of the calibration of these is dependent upon the accuracy of the analyte value ascribed to the reference coal.

Research is presented here to validate an instrumental method for analysis of sulfur in coal following calibration using a synthetic calibrant. Introduction of such methods would gradually eliminate the use of potentially inaccurate reference coals as calibrants for the analysers used in instrumental methods of sulphur analysis. The work completed in this study includes:

· The search for suitable sulphur compounds;

· The preparation and evaluation of suitable calibrants;

· Laboratory trialling of a potentially new analysis procedure.

A method was developed to calibrate a typical instrumental sulphur determinator, which was then used to analyse coal samples of known sulphur contents. The developed method was found to be capable of determination of sulphur values with similar levels of precision to those currently measured by instrumental sulphur determinators, which were calibrated with certified reference coals according to AS1038.6.3.3. Further work is required to complete validation of the method, but once fully validated and introduced to the coal industry, accuracy in sulphur determinations should be improved, as any systematic errors will be removed from methods requiring calibration with certified reference coals.

The additional method validation work required includes further work on high sulphur content coals, more testing of synthetic calibrant stability, completion of an inter laboratory testing program on a set of coals with known sulphur contents and development of a draft Standards Australia method to determine sulphur in coal using a synthetic calibrant method. Following likely development of a new Standards Australia method, it is also recommended that relevant Standards Australia methods that require calibration with reference coals be withdrawn or suitably changed.

It is further recommended that in order to eliminate possible errors associated with production of the synthetic calibrant by commercial laboratories, batches of the calibrant should be prepared, validated and marketed to the Australian coal industry by a qualified authority. However any new standard method will include methodology for preparation of this synthetic calibrant.