There are two a few points to consider:
The reduction of Copper Sulphides, commonly present in coal seams and
therefore in coal waste, works in favour of thermodynamics, therefore the
energy needed to reduce CuFeS2 to Cu+Fe+SO2 is very slight and can occur in
the presence of air (oxygen) at the Earths surface, this is a common problem
in Copper Sulphide waste heaps in Copper mines and also underground where it
can cause spontaneous combustion. Copper Sulphide is also added in furnaces
to drive up the temperature. This reacton produces heat, and only a small
rise in heat can lead to ignition of methane between 4-10% and then at
higher concentrations >40%, this is why underground coal mining machinary
contains scrubbers and exchange surfaces to stop the exit of anything hot
into the air that is likely to cause ignition of the methane, it is also why
you cannot operate a coal mine in concentrations of methane above (i think
in UK) 1.5%, hence why many coal mines only worked a 4 day week as by friday
the concentration of methane in the air was too high to allow safe
extraction. In the coal waste heaps one would imagine that the methane
concentration is >40% and that air can be readily circulated through its
permeable nature, its probaly best if you look up the thermodynamics of
Copper Reduction for more detail.
Hope this of some help
Robert
-----Original Message-----
From: D.R.Poyner
To: [log in to unmask]
Sent: 01/04/2003 13:35
Subject: Re: Spontanious conbustion in coal mining tips
I discovered the extent of my ignorance a few weeks ago when I was
asked by a geologist to explain exactly why spontaneous combustion
takes place and was reduced to hand waving and vague talk of pyrites.
Can someone explain the role, if any, of sulphur containing compounds
in spontaneous combustion? Is their oxidation relevant to the process?
David Poyner
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