Aeration and Temperature Control
Air supplied to the GEOCOAT® heap
serves two purposes:
- Provides oxygen for bacterial and chemical oxidation of the sulfide minerals
- Removes heat by evaporating water, allowing heap temperatures to be controlled within the optimum range for biooxidation.
Heat is removed from the system by the saturated air
as it leaves the top of the heap and by irrigation
solution leaving the bottom of the heap. The extent
to which heat is removed by this saturated air is
dependent on the rate at which air is put into the
heap, and by the temperature and relative humidity
of the ambient air. Heat is also lost from the system
by cooling of the solution as it contacts the incoming,
unsaturated air flowing into the heap, and from
the solution ponds and as the solution is returned
to the heap via the sprinklers.
The specific flow rate of the air supply and distribution system depends on the mineralogical and chemical composition of the concentrate, the coating ratio (or the quantity of sulfide per unit volume of heap), the rates of reaction of the sulfide minerals, and the ambient conditions at the project site.
Low-pressure fans, equipped with variable-speed drives to minimize energy consumption, supply air to the heap via perforated HDPE distribution piping.
The sulfide oxidation reactions are exothermic, which raises the temperature of the heap. Depending on the mineralogy of the concentrate, and the microorganisms used, the optimal temperature of a GEOCOAT® heap ranges from 25-70°C. The rate of heat accumulation is optimized using GeoBiotics' HotHeap™ technology,which keeps the heaps at the target temperature throughout the leach cycle.