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Chromium in Australian export thermal coals
An examination of chromium in Australian export thermal coals intended for industrial, scientific and research audiences.
21 July 2010 | Updated 14 October 2011
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 chromium in Australian export coals, other internationally traded coals, the Earth's crust and shales.
| Concentration of chromium in: ||mg/kg |
| Australian export coals ||2 - 24 (9) # |
| Other internationally traded coals ||1 - 34 (13) # |
| Earth's crust ||100 |
| Earth's shales ||100 |
| # values in parentheses are averages |
Chromium has been identified as a Hazardous Air Pollutant (HAP) by environmental authorities.
Modes of occurrence
There is significant uncertainty about the most likely association of chromium in bituminous coals. Chromium is present in Cr (III) forms but may be associated with sulfides, organic matter or clays.
Behaviour during combustion
Chromium is partly volatile and may condense on the fly ash particles. There is little enrichment on the fine particles. Chromium is predominantly present in the Cr(III) form in power station ash.
Health and environmental effects
On the spectrums:
for the NPI health hazard of 0-3, Cr (III) compounds registers 1.2
for the NPI environmental of 0-3, Cr (III) compounds registers 2.0
for the NPI health hazard of 0-3, Cr (VI) compounds registers 2.5
for the NPI environmental of 0-3, Cr (VI) compounds registers 3.0.
Chromium as Cr (VI) is a concern if released into the environment. Total chromium is low in coal ash and the fraction present as Cr (VI) is small.
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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