• Modes of occurrence 
• Behaviour during combustion 
• Analytical methods 

Trace elements in coals may be associated with specific minerals or with organic 'coaly' matter.

The sources of trace elements include biological material (plants, algae and bacteria) that is the precursor of the coaly material, water in the peat swamp and mineralogical material washed or blown into the swamp.

Table representation of thorium in Australian export coals, other internationally traded coals, the Earth's crust and shales.

Concentration of thorium in:	mg/kg
Australian export coals	0.5 - 6.9 (2.6) #
Other internationally traded coals	<0.1 - 21 (3.0) #
Earth's crust	10
Earth's shales	12
# values in parentheses are averages

 

Thorium has been identified as a Hazardous Air Pollutant (HAP) by environmental authorities.

Modes of occurrence

Thorium is present in the minerals monazite and to a lesser extent in zircon and possibly xenotine. Small amounts could be present in iron oxides and clays.

Behaviour during combustion

Thorium appears not to be volatile during combustion; it is not enriched on the finer ash particles.

Analytical methods

There are a number of standard methods for determining thorium in coal.

AS 1038.10.0, Australian Standard, Coal and coke - Analysis and testing - Part 10.0: Determination of trace elements – Guide to the determination of trace elements.

ASTM D6357-00a Test Methods for Determination of Trace Elements in Coal, Coke, & Combustion Residues from Coal Utilization Processes by Inductively Coupled Plasma Atomic Emission, Inductively Coupled Plasma Mass, & Graphite Furnace Atomic Absorption Spectrometries.

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