Management of spontaneous combustion in coal overburden spoil piles

Author(s): 
Andrew Garvie, Ken Donaldson, Basil Beamish, Brad Williams
Date: 
Monday, February 18, 2019
First presented: 
Coal Operators' Conference 2019
Type: 
Published paper
Category: 
Mine Waste

Laboratory testing was undertaken to examine the spontaneous combustion propensity of some of the coal seams being mined at Leigh Creek. Tests indicated that while carbonaceous rocks retained a fuel load, in isolation, these did not have the capacity to reach thermal runaway. However, the potential existed for heat from another source, such as coal, to raise the temperature of these rocks to above the threshold for thermal runaway (>100 °C).

The mine closure plan submitted to the regulator (Department of Premier and Cabinet, South Australia) incorporated a monitoring trial of the selected spontaneous combustion management rehabilitation strategy to demonstrate its effectiveness. The strategy included reducing batter slopes of waste spoil piles and the application of an inert cover. The trial was established in June 2017 in a location with active combustion immediately prior to rehabilitation treatment. Measurements of temperature and oxygen concentrations within the spoil pile over twelve months show that oxygen is consumed within 1 m of the outer surface of the waste, while maximum spoil pile temperatures have been decreasing, indicating a net heat loss from the trial spoil pile area. No spontaneous combustion outbreaks have occurred in the trial area since the trial commenced. Characteristics of the trial area materials, the management strategy, and outcomes from the field trial measurements are presented.

Feature Author

Andrew Garvie

Andrew Garvie has more than 24 years’ experience providing scientific and technical assessments in acid and metalliferous drainage (AMD) and heap leach oxidation.  More recently he has undertaken assessments of self-heating and the potential for spontaneous combustion of coal wastes and carbonaceous black shales associated with sulfide minerals.  Studies have included the quantification of physical processes that support the oxidation of mine wastes and heap leach piles by measurement and predictive modelling.  He has assessed strategies used at mines to control oxygen supply and water flux into dumps and heap leach piles using the same methods.  Andrew’s experience includes use of geostatistics to assess the adequacy of sampling, geochemical characterisation to examine the potential of mine wastes to produce AMD, and assessment of contributors to pit lake water quality, including wall rock oxidation and in-pit waste rock disposal.  He has applied his understanding of the above processes to the development of conceptual waste landform closure strategies for the control of AMD production and spontaneous combustion.

Principal Consultant (Geochemistry)
PhD (Physics), MAusIMM
SRK Sydney
SRK United Kingdom