Trace Elements in Coal; Status of Test Methods in Use and their Applicability

 STAGE 1 REPORT

The key objectives of this stage of the project were to:

• Determine if Australian laboratories are meeting expected accuracy and precision requirements of ISO standards;
• Determine if precision and accuracy levels being achieved meets the requirements of the Australian coal industry, taking into account trends in environmental and trading restrictions; and
• Ascertain if the range of (certified) reference materials (RMs) for these elements in coal matrices meets the quality assurance needs of the Australian coal industry and thereby builds confidence in the accuracy of the analysis of these trace elements.

An industry survey associated with this project indicated that the published levels of precision in relevant Australian and ISO standard test methods typically meet the needs of Australian coal industry.

The ability of Australian laboratories to meet the accuracy and precision requirements of ISO standards, and whether there are an adequate range of RMs, to build confidence in the accuracy of analyses depends very much on the parameter in question. This aspect was assessed by the conduct of an interlaboratory study (ILS) in which a range of RMs were submitted blind to participating Australian coal testing laboratories and an associated laboratory survey. The number of participants was parameter dependant ranging from four to ten and resulted in insufficient data to draw firm, statistically sound conclusions for parameters other than chlorine. The results from this ILS, and its associated laboratory survey, indicate a high level of confidence in the accuracy and precision of chlorine analysis. For the remaining parameters where the number of participants is less than ideal, results are considered interim and can be summarised in the report.

Although interim, any potential identification of bias or reduced precision should be of concern to the Australian coal industry and worthy of further monitoring to establish if any identified trends are due to inherent bias or are within the normal fluctuations of method precision. For arsenic, cadmium, fluorine, mercury and selenium where industry concern is highest further rounds of testing need to be conducted to determine if identified problems have been remedied and provide more robust conclusions to support the findings of this study. Key risks to achieving this objective are the availability of suitable samples combined with the possible variability in laboratory precision over time. Ultimately this work should provide confidence that the analysis of these elements by Australian laboratories is meeting required levels of precision. Alternatively, it may identify where analytical methods need to be reviewed, either within laboratories or at the national level. Furthermore, this stage of the project initially focussed on the precision and bias of the analytical methods and did not address the likely errors that might results from sampling and sample preparation.

Stage 1 of the project provided a detailed evaluation of the status of trace element testing at a point in time. There is a high level of confidence in the analysis of chlorine in coals. For other trace elements, research outcomes are interim and more variable.

STAGE 2 REPORT

The outcomes of stage 1 indicated additional work was required to provide a more comprehensive data to draw reliable conclusions on the confidence level that the Australian coal industry can place in the trace element results from Australian coal testing laboratories. This defined the objectives for stage 2:

• To provide confidence in the level of precision and accuracy for analysis of As, Cd, F, Hg and Se performed by Australian coal testing laboratories; and
• To evaluate the potential for bias on fluorine for a wider range of Chinese coal reference materials.

Stage 2 undertook the following:

• Australian coal samples and an appropriate range of reference materials including a range Chinese fluorine reference materials were obtained.
• Laboratory Survey - designed to identify departures from procedures used in Stage One of this research.
• An Interlaboratory Study (ILS) was conducted over 3 rounds, 8 weeks apart, amongst those Australian laboratories.

The results from the ILS were analysed using a range of precision and accuracy assessment parameters.  There were two objectives of the ILS:

• to provide confidence in the level of precision and accuracy for analysis of As, Cd, F, Hg and Se performed by Australian coal testing laboratories. The ILS has not provided complete confidence that Australian coal testing laboratories can provide trace element analyses at the required level of accuracy and precision. The industry can have confidence in Fluorine and Mercury analysis but not for the other analyses. All analyses other than Fluorine show that 1 or 2 laboratories for every test had poorer results than the other laboratories and considering the small number of laboratories performing the test, impacts significantly on industry confidence levels in the results. Selenium had the lowest confidence results; most laboratories experienced some level of difficulty at various times.

• To evaluate the potential for bias on fluorine for a wider range of Chinese coal reference materials. The testing of additional Chinese reference materials still indicates that the potential for bias on fluorine still exists. The average bias on samples tested to date is of the order of 5% low. The presence of bias however is not conclusive as not all samples tested exhibited this bias.