Dual aeration tests with heap leaching of a pyrrhotite-rich pentlandite ore

A large-scale investigation into the effect of increased aeration on heap leaching of a pyrrhotite-rich pentlandite ore was commenced at the Terrafame mine in Finland. The typical reference air feed amount in operation is approximately 0.05 m ³ /metric ton/h, fed from one direction of the 330 to 350 m wide heap. In the current study approximately 62% higher air feed vs. reference operation was trialed by installing another layer of aeration from the opposite direction of the heap. The hypothesis was that air distribution across the ore would be improved and that the increase in air feed would result in faster oxidation of pyrrhotite, leading ultimately to improved recovery of valuable metals. The heaps were observed for 150 days after stacking. The results revealed an increase in the leaching rates of several metals: manganese, magnesium, iron, nickel and zinc leached 14, 171, 142, 1932, and 1309% more in the presence of extra aeration during the observation period. In addition, applying the extra air showed a 324% increase in the generation of acid within the heap.