The effects of simulated stacking phenomena on the percolation leaching of crushed ore, Part 2: Stratification

Unstratified and artificially stratified samples of oxide-copper ore were percolated with water followed by acid leaching in a custom-made laboratory apparatus. During two consecutive experiments run over collectively 335 days, stratification actually increased the width over which solution distributed throughout the ore, opposed to the expectation that it would be detrimental to solution distribution. However this did not manifest in a measurable or reproducible difference in rate or extent of copper extraction or of gangue acid consumption. The increase in effective dripper spacing was the only variable studied which clearly exhibited an influence over rate and extent of extraction. This is already qualitatively known and utilised in the scale-up from columns to cribs and to large heaps. However the present study provides a quantified case study where the 153 mm diameter columns used in Part 1 yielded a dual-porosity diffusion time (Gamma) of around 5 days and extractable (kappa(x)kappa(w)) fraction of about 100 percent. In contrast, the wide boxes used for Part 2, representing 900 mm dripper spacing, yielded Gamma > 10 days and kappa(x)kappa(w) = 60(+/- 12)%. In contrast, little difference was noted between the leaching of stratified versus un-stratified ore. The poor predictability observed for the gangue acid consumption (GAC) rate constant needs to be borne in mind if predictive modelling is attempted. Since GAC competes with the copper leaching reaction for acid, it also exhibits an important influence over the rate of oxide-copper extraction.