Deep well rinsing of a copper oxide heap

• A pilot scale project involving subsurface leaching with rinse wells is described for a copper heap.
• Local monitoring of hydraulic and metallurgical parameters ensured success.
• It is estimated that nearly 200,000 lbs of copper was liberated.
• Plans are to upscale the project across the entire pad.

A subsurface irrigation test, using a series of four rinse wells, was conducted on a copper oxide heap leach pad over a three week period. The pad has been significantly underperforming due to difficult drainage conditions imposed by a high degree of fine-grained material. The test was to determine whether it would be feasible to conduct the directed leaching method across the entire pad assuming that enough copper is liberated to pay for the upscaled well field installation. The rinse wells were connected directly to an existing raffinate line. Validation of the test included 1) hydraulic monitoring to ensure sufficient solution flow and coverage in the formation and 2) metallurgical monitoring of solution samples extracted from nearby monitoring wells to ensure copper liberation. The results showed that the mean flow rates to each rinse well exceeded expectations by a factor of at least 1.5 for an extended period of time, that radial solution coverage for optimal operating conditions was approximately 17 m, and copper grade was upwards of three times the anticipated grade. The test was then extended for an additional two months on a single well, where the copper grade remained approximately two times higher than that from surface irrigation. By the end of the testing, it was calculated that at least 191,000 kg of copper was liberated. The upscaled program is to include 170 additional wells spaced 31 m apart and the potential for 12 wells to be rinsed simultaneously, which would allow the program to be completed in less than three years.