Oxygen liquid-film mass transfer in heap leaching

The oxygen mass transfer coefficient from air to percolating leach solution (kLa) in barren gravel and sulphide ore was measured at various temperatures, air flow rates, and irrigation rates. The effect of agglomeration was also studied. The kLa value increased with increasing irrigation rate and increasing temperature, but decreased with increasing particle size. The kLa value was independent of the aeration rates used, which were very high. A correlation was derived for kLa with Reynolds number, oxygen diffusivity, and particle size, both in the case of unconsolidated beds of defined particle sizes, and for agglomerated ore having a distribution of particle sizes. Values of kLa showed a high degree of variability, so that more than 1000 measurements were required to establish the correlation presented in this study. Values of kLa measured in this study were as high as 1 s− 1, suggesting that bio-heaps may not be oxygen mass transport limited. The findings have particular significance to acid rock drainage and bio-heap leaching.