New Method for Determining Chlorine in Coal

A new reference method based on x-ray fluorescence spectrometry has been developed to more accurately measure chlorine in coal.  Accurate chlorine measurement is critical for some coal producers. Elevated levels of chlorine in coal can cause corrosion problems as well as having the potential to exceed air emission limits. Although there are a large number of national standard methods for determining chlorine in coal, large discrepancies  occur between the methods and between laboratories using the same method.  Some Australian coal producers have been penalised because the chlorine levels recorded by their customers have differed from the results received from their own coal analysis laboratory.

Project Objectives

The objectives of this research are to:

• Develop an accurate reference method for determining chlorine in coal

• Critically assess current standard methods and identify their limitations
• Investigate suitable alternative sample preparation methods
• Produce a range of standard reference coals with certified chlorine values to be used by commercial laboratories to monitor quality control and provide quality assurance for the methods used.

Findings

The limitations of existing standard methods have been critically assessed in collaboration with commercial laboratories. The major problems identified were the poor sensitivity and reproducibility inherent in the procedures. The researchers recommend that the most commonly used Australian standard method (AS 1038.8.1) be modified to incorporate ion chromatography or inductively coupled plasma atomic emission spectrometry to determine the chlorine in the final collector solution.

Ion chromatography and inductively coupled plasma atomic emission spectrometry can better detect limits and, therefore, are more reliable at the 100mg/kg level than conventional methods. While the researchers recommend using these models, they accept that commercial coal analysis laboratories do not commonly use these methods to determine chlorine levels.

The researchers have also developed a new reference method based on x-ray fluorescence spectrometry (XRPS), which has been validated using instrumental neutron activation analysis (INAA). Agreement between the two techniques is within 10% over a concentration range of 100 to 1500mg/kg. INAA and XRFS offer high sensitivity with good detection limits for chlorine. The major advantage is that they are non-destructive and, therefore, do not rely on extraction of the chlorine.

Three standard reference coals with certified chlorine concentrations ranging from 0.04 to 0.12 percent are now available to commercial laboratories.

Where To From Here

Laboratories using existing standard methods need to involve a high level of quality control to ensure the methods are being operated correctly. The availability of reference coals will be useful for this purpose. The reference coals should also be valuable in resolving disputes between laboratories and conducting inter-laboratory round robins on national and international bases.