Experts from the Earth Science Research Centre at Sultan Qaboos University have come up with scientific explanation for the smoke emissions from a closed copper mine in Shinas area in the Sultanate of Oman. Recently rumors have been spread in social networks about hot gas emissions from a closed copper mine in Shinas. Prof. Sobhy Nasr, Director of the Earth Science Research Center at SQU, said the smoke in the area is resulting from burning of sulphides in the closed mine due to humidity of the atmosphere and oxygen uptake and other natural conditions.
Prof. Sobhy Nasr said that several previous studies about copper sulphide mine residues such as those Shinas have shown that moisture in the air and ambient temperature can be increased due to self-combustion of the sulphides in such mines. This occurs if the self-heating and reaction of these minerals with the water in the mines for a long period and with precipitation and high water level.
Quoting past studies Prof. Sobhy Nasr said that humidity of air and ambient temperature can increase self-heating of sulphides. Self-heating of sulfides may increase the temperature and may lead to spontaneous combustion, which is particularly difficult to control. Active ores that were left in underground mines for a prolonged duration oxidized rapidly and self-heated. Problems are also encountered during crushing and handling processes, where sulphide ores are commonly introduced to humid air and oxygen, promoting self-heating. Self-heating of sulphides was also periodically reported during storage and transportation. Self-heating is an exothermic oxidation reaction. A material is self-heating when heat generated within the material, without external heat input, is greater than the heat being dissipated to the surroundings. Pyrrhotite and pyrite have been reported as the most reactive and prone to self-heating out of other sulphide minerals due to the high iron-deficiency.
Numerous factors account for sulphides to become self-heating in nature. Some of the major factors are humidity of the atmosphere, moisture content, oxygen uptake, particle size, pyrrhotite content, ambient temperature and pH. Each factor contributing to self-heating is irrelevant from one and another and that is what makes the self-heating process very interesting and complex. “The sulphides are exposed to both moisture and oxygen, conditions that promote partial sulphide oxidation and the formation of elemental sulphur. The self-heating of sulphides leads to formation of ‘hotspots’ within storage piles”, Prof. Sobhy Nasr said.