Phosphorus In Coal: Status Of Test Methods In Use And Applicability To Industry Needs

The specific objective of this study was to assess whether laboratory testing of phosphorus in coal is meeting current and future industry needs, or if further work is required in this area.

This project established that a range of analytical methods are currently in use, or under development by Australian laboratories. These include colorimetric and X-ray fluorescence (XRF) techniques analysing phosphorus directly in coal or indirectly from coal ash.

A limited proficiency test program was conducted to provide an initial assessment of the relative performance of each of those methods. This was compared with the outcomes of an industry survey to establish if the coal industry has the appropriate analytical methods to meet current and future needs. A further objective was to provide information on the need for alternative procedures based on ongoing safety concerns around the use of hydrofluoric acid (HF).

The preliminary research identified an indicative bias between the phosphorus methods of up to 13% relative difference albeit based on a limited data. This, and the poor precision of standard methods of phosphorus analysis, has commercially significant implications.

Suitability of current phosphorus test methods with current and future industry requirements and whether the indicative precision of the various method(s) is acceptable for industry needs  -  Whether or not phosphorus test methods are meeting industry requirements appears quite dependant on which organisation this question is directed at. Indications are, that for two-thirds of industry, current phosphorus analysis methods are considered acceptably precise. However, there are some who expressed clear concerns that analytical turnaround times and the relatively broad tolerances of standard methods for phosphorus analysis are not acceptable citing the commercial significance of poor method precision in particular where phosphorus levels are tied to contractual penalties.

Whether further work is justified on any of the standard or non-standard method(s).  Given concerns around whether phosphorus analysis methods are meeting industry needs, and indications from the proficiency test program that a bias between methods of analysis may exist, further work in this area is warranted. There is a trend toward the use of XRF methods of analysis particularly in response to customer demands for improved analysis turnaround times in production situations where high phosphorus coals require blending. A number of reasons were documented indicating why reduced levels of precision and accuracy and/or errors of analysis can be introduced using these techniques for light elements such as phosphorus. Introduction of a standard XRF method for direct analysis of phosphorus in coal is therefore justified.

It is recommended that further research is warranted. Recommendations for continuation of this research would entail the conduct of a more comprehensive program to determine if the bias between methods is statistically significant.