Case Study – Enhanced Recovery of Copper

The end of a heap’s life rarely means that all of the ore has been wetted and every ounce of metal has been extracted. Through our heap characterization efforts, we have identified large compacted portions of ore, which are significant in their ability to reduce permeability and prevent effective wetting and leaching. Enhanced metal recovery using subsurface leaching is a means to recover those lost ounces prior to mine closure. HGI has been helping to design, monitor, and verify the effectiveness of subsurface leaching projects in heap leach facilities for nearly a decade. Our work has been conducted on gold, copper, and silver heap leach pads in a number of North American mines. The work can easily be extended to cover uranium, nickel, and other metals.

Enhanced metal recovery with subsurface leaching is a means to recover lost copper from compacted ore, prior to mine closure. HGI has been helping design, monitor, and verify the effectiveness of subsurface leaching in heap leach facilities for nearly a decade.

Recently, HGI has been helping a copper heap leach facility in Arizona with its end-of-mine plans. A pilot scale injection project that included four deep rinsing wells and nine monitoring wells was tested to see if applying raffinate directly to ore under moderate pressures (i.e., rinsing) can increase liberation and eventual recovery. For the test, raffinate lines were connected to wells that penetrated 70 to 100ft into the heap. The wells were specifically designed for the heap material, expected pressures, and flow rates. The subsurface leaching test lasted for several months, over which time approximately 50 million gallons of solution was introduced to the subsurface. Heap monitoring was conducted geophysically, using the Geotection resistivity system, and metallurgically, with the Mobile Solutions Lab. The photos below show equipment and processes for the rinsing for enhanced metal recovery. A paper has also been published on the pilot test.

Photos from an enhanced metal recovery project on a copper mine

Given the success of the pilot scale injection test, enhanced metal recovery at the mine has been consistently ongoing. As of 2018, we have over 200 injection wells and 50 monitoring wells with more planned in 2019. Throughout the process, data continues to be gathered to keep an economic justification as well as ensure the safety of the facility. An interim paper was published to describe this ongoing effort.

Given the success of the pilot scale injection test, enhanced metal recovery at the mine is ongoing. HGI remains heavily involved with well design, drilling oversight, data processing, and heap characterization.

Data plots below are a testament to the power of enhanced metal recovery if done correctly. From upper left to lower right, we show cumulative injection/rinse volume by area, daily copper produced from rinsing (when considering copper grade in monitoring wells and seeps), cumulative copper production (in million pounds), and estimated percent recovery when considering the inventory of each area. When metal recovered is considered against costs to implement, the return on investment is over 5:1.

Data from an enhanced metal recovery project on a copper heap