Effect of Ambient Conditions on Self-Heating Characteristics of a Ni-Cu Sulphide Ore

Self-heating characteristics of a complex nickel-copper sulphide ore stockpile containing pentlandite, chalcopyrite and pyrrhotite have been investigated through continuous monitoring of its inner temperature over a 7-month period (May to December). Variation of external weather parameters such as air temperature, dew point, wind velocity, air humidity and atmospheric pressure are reported. The inner temperature of the stockpile varied from 10.5 degrees C to 44 degrees C. One reason for the maximum temperature to be relatively low is related to lack of reactive surface area since amount of fines in the stockpile is limited. The inner temperatures indicated significant fluctuations due to rapid changes in ambient conditions, particularly the outside temperature, which ranged from -5 degrees C to 32 degrees C. Despite an apparent parallelism between these two types of temperatures, occasional occurrences of rapid decrease in the ambient temperature while the stockpile was still in a self-heating mode were notable. These rapid cooling effects on the stockpile had a retardation effect on trends of increasing inner temperatures. Regular rain showers that the stockpile area received may have also played a role in dissipation of heat, especially when the stockpile experienced a heavy rain. The loss of pentlandite recovery due to stockpile oxidation was about 6.2% compared to 4.0% for chalcopyrite. These losses have been attributed to over-oxidation of these minerals primarily based on development of ferric hydroxy oxide species such as goethite and precipitation of hydroxides of various metal species mobilized as a result of oxidation. Interestingly, floatability of pyrrhotite has been enhanced by stockpile-oxidation. Thus, the flotation selectivity shifts in favour of pyrrhotite for the oxidation case. This behavior was attributed to metal-activation and elemental sulphur/polysulphide formation due to oxidation of the sulphide part of these sulphide minerals. Relative amounts of hydrophilic to hydrophobic species on the surfaces are responsible for observed bench scale behavior.