Coal, and particularly brown coal, is very reactive to oxygen, and will generate CO2 and that creates heat.Īs the coal gets hotter it will eventually get to flame temperature and that coal will burn." "Spontaneous combustion is a well understood phenomenon.
While coal fires can be triggered by external sources of heat such as bushfires and lightning strikes, they can also start spontaneously as the coal oxidises, says Cliff. Meanwhile, hydrogen in the coal is converted to water vapour, nitrogen to nitrogen dioxide and sulphur to sulphur dioxide. This is a thick-seam coal mine, 30 metres thick and very close to the surface so anything that intrudes into the mine will set fire to the seam," says Cliff.Ĭoal is made up of carbon (between 60 and 90 per cent - higher grades contain more carbon than lower grades), hydrogen (6 - 7 per cent), oxygen as well as very small amounts of nitrogen and sulphur.Ĭoal fires are created by the interaction of carbon, oxygen and heat, which in turn produces carbon monoxide, carbon dioxide, and more heat to fuel the reaction.
This Victorian brown coal is a low rank coal, geologically young, and very prone to being ignited. "Unlike timber, coal when it gets hot has massive thermal mass which is very hard to extinguish.
Such coal fires, says University of Queensland mining safety expert Professor David Cliff, are much harder to put out than burning bushland. In Morwell in Victoria, bushfires have ignited the coal seam face in an open cut mine which supplies a nearby electricity plant. The results provide a preliminary assessment of the types of REE-bearing minerals and potential leachability of coal seam underclays from the Central Appalachian basin.The bushfires burning across Australia during this long hot summer pose a particular risk to areas where coal is being mined. Citrate solution leaching of underclay produces a PLS with lower concentrations of gangue elements and higher concentrations of REE than achieved with hydrochloric acid or sulfuric acid. The citrate PLS produced from leaching specific underclay powders contains relatively higher concentrations of REE and lower concentrations of gangue elements compared to PLS produced from sequential digestion using ammonium sulfate and mineral acids. The leaching method described here uses a chelating agent, the citrate anion, to solubilize elements that are adsorbed, or weakly bonded to the surface of clay minerals or other mineral solid phases in the rock. Laboratory bench-top and flow-through reactor leaching experiments were conducted on underclay rock powders to produce a pregnant leach solution (PLS) that has relatively low concentrations of gangue elements Al, Si, Fe, and Th and is amenable to further processing steps to recover and produce purified REE product. This study utilizes a suite of analytical techniques and benchtop leaching tests to characterize the properties and leachability of the coal seam underclays sampled. Underclay rock associated with Central Appalachian coal seams and prevalent in coal utilization waste products is an alternative source of REE to hard rock ores that are mainly composed of highly refractory REE-bearing minerals. To support the emerging need, it is necessary to identify new domestic sources of REE and technologies to separate and recover saleable REE product in a safe and economical manner.
Rare earth elements (REE) are necessary for advanced technological and energy applications.