The Leigh Creek Coal Mine, located approximately 500 km north of Adelaide in South Australia, operated between 1944 and 2015. During operations localised spontaneous combustion occurred on numerous occasions in the overburden spoil piles containing relatively small volumes of coal (about 0.8%). The majority of the overburden sequence consisted of sandstones and carbonaceous mudstones. Samples of overburden rocks had total sulfur and total organic carbon present at up to 2.2 and 14 wt% respectively.
At the end of mining surface temperatures of up to 200°C were measured and laboratory testing demonstrated the potential for self-heating and spontaneous combustion of both coal and overburden material in the spoil piles. The management strategy selected for preventing spontaneous combustion post closure included reducing the batter angle of the spoil pile and covering with a layer of fine inert material.
A trial of the management strategy was established in June 2017 in a location that was actively combusting immediately prior to reducing the batter slopes and placement of the inert cover. Measurements of temperature and oxygen and carbon dioxide concentrations in the spoil pile over 20 months show that:
- most oxygen is consumed in the top 1 m of waste,
- carbon dioxide production rates have decreased and are consistent with historic combustion and ongoing oxidation of the carbonaceous mudstone,
- overall there has been a net heat loss from the spoil pile and
- temperatures have decreased below the threshold required for the initiation of spontaneous combustion.
Spoil pile conditions before and after the implementation of the management strategy are presented and an assessment of the effectiveness of the management strategy is provided.
