Effect of Initial Irrigation Conditions on Copper Heap Leaching

Heap leaching of ores is becoming a widespread method of metal recovery. It is common practice to initiate irrigation in heap leach facilities with low rates, followed by a gradual increase to the final rate. However, no detailed study has been performed to understand the processes that may lead to better recovery using this technique. Large column tests were performed with copper ore and raffinate solution to study solution-flow behavior under different initial irrigation ramp-up schemes. The columns were monitored for the duration of the tests with moisture sensors, a neutron probe, electrical resistivity tomography, and tensiometers. The baseline test used the final target raffinate irrigation rate from the beginning. The packed ore experienced significant agglomeration collapse, consolidation and decreased permeability, localized ponding, and flow diversion. The slow ramp-up test exhibited minimal ore collapse and no ponding or flow diversion, such that the flow was observed to remain in the center. The faster ramp-up test showed some ore collapse, but no ponding or flow diversion. Water content did not seem to be the only factor involved in agglomeration structure collapse, suggesting that other factors such as pore size variation and flux might take key roles. The results of tracer tests and inverse transport modeling helped to understand flow behavior for the tests. Large dispersivity values resulted from the large scale and wide pore size variation of the ore media. Mobile water fraction and mass transfer coefficients were consistent with compacted ore versus agglomerated structure from the tests. The experimental results, along with the inverse modeling helped in the interpretation of the hydrological processes in heap leaching