Standard Analytical Methods for Trace Elements in Coal

The levels of trace elements in thermal coals are coming under increased scrutiny by power generating companies because of the potential environmental impact from atmospheric emissions of trace elements and their leaching from ash disposal systems. In some countries there are legislated discharge limits for coal-fired power plants and this has focussed attention on the levels of trace elements of environmental concern in feedstocks. This has direct implications for the Australian coal industry as there is an increasing requirement for exporters to specify the levels of environmental trace elements in thermal coals.

• Arsenic, selenium and antimony by fusion followed by atomic absorption / fluorescence spectrometry Boron by fusion followed by inductively coupled plasma mission spectrometry. 

• Other trace elements including beryllium, copper, chromium, cobalt, nickel, manganese, molybdenum, lead, vanadium and zinc, by fusion followed by inductively coupled plasma atomic emission spectrometry.

The methods tested were unsuitable for determining mercury and cadmium because of the low levels present in Australia coals.

The new methods are superior to previous Australian Standards in that they cover more trace elements of environmental concern. They are more sensitive by a factor of about 10 which makes them applicable to the analysis of trace elements at the levels normally encountered in export thermal coals.

The methods are currently being circulated for public comment by Standards Australia with the expectation that they will be formally adopted as Australian Standards and issued mid-1997.

Introduction

There are increasing concerns about the potential environmental impact of trace elements from coal-fired power stations. These relate to the release of trace elements as atmospheric emissions and the potential to impact on the ecology from waste disposal sites. The United States National Research Council (1980) classified a range of trace elements, present in coal, according to their known adverse health effects and toxicity to plant life.

Elements which were considered of major concern were also classified. Elements of moderate concern included vanadium, chromium, nickel, copper and zinc. More recently amendments to the United States Clean Air Act (1990)identified eleven trace elements, commonly found in coal, as potentially hazardous air pollutants (HAP). These elements are beryllium, chromium, manganese, cobalt, nickel, arsenic, selenium, cadmium, antimony, mercury and lead.

Although the Act relates to industrial discharges generally and not specifically coal-fired power plants, it requires power station operators to monitor mercury emissions.

Following the amendments, the Electric Power Research Institute (Boutacoff, 191) has undertaken a major survey of trace element emissions from power plants in the PISCES project.

The identification of these elements has led to increased interest in the levels present in coals used for electricity generation. As a consequence, this may be seen as advantageous to Australia's thermal coal export market in view of the relatively low levels of environmentally sensitive trace elements present in product coals compared to those of its major competitors (Dale, 1995).

In order to demonstrate the environmental acceptability of Australian export thermal coals, it is necessary to specify the levels of key environmental trace elements using reliable and accurate analytical methods. This is particularly important in complying with contractual specifications.

To meet these requirements standard methods of analysis, accredited by Standards Australia (SA) or the Organisation for International Standardisation (ISO) are necessary. These standards have been subject to rigorous examination and testing to ensure their suitability for general use by laboratories.

In a previous research project, C3015 - New Approach to Determining Trace Elements in Coal (Dale and Riley, 1995) - funded by the Australian Coal Association Research Program, deficiencies in current national and international standard methods for trace elements were identified.

These related to lack of sensitivity which basically excluded their application to the analysis of product thermal coals because they were not suitable for determining the environmentally sensitive trace elements at the levels normally present.

For some of the most important elements no standard method existed. In addition, many of the current methods were based on old analytical technology. This project addressed these problems by applying modern techniques of analysis which were of sufficient sensitivity and reliability to accurately determine the low levels present in Australian thermal coals.

The inadequacy of current standard methods was highlighted by the variable performance of laboratories which participated in a round robin trial conducted in Project C3015. Further evidence of the problems with the current national and international standard methods emerged from this laboratory's participation in international round robin trials conducted by the Canadian Centre for Mineral and Energy Technology (CANMET) over the past 5 years.

The major significant outcome from project C3015 was the development of reliable and accurate methods based on modern analytical instrumentation covering all the trace elements of environmental concern. Based on these successful outcomes, this project sought to establish new Australian standard methods which were more accurate and reliable than previously.

The major aim of the project was to establish these new methods as Australian Standards accredited by Standards Australia. The work was coordinated through the MN/1/1 Working Group on Trace Elements which organised validation trials involving a number of participating laboratories. To receive national accreditation, the methods had to satisfy the rigorous requirements of Standards Australia in respect of robustness and suitability for use by commercial laboratories.

Conclusion

The new standards have been satisfactorily validated according to Standards Australia during 1997. These new standards are superior to previous methods in that they are accurate and reliable for determining a range of trace element at the levels normally present in Australian export thermal coals.

All trace elements of environmental concern, with the exception of mercury and cadmium, are now covered by these new methods. They provide the coal industry with good quality assurance in the specification of the levels of trace elements in thermal coals destined for the export market. This should provide the industry with a competitive edge in the marketing of Australian thermal coals.