Aerial view of the conventional flotation, thickening and filtration circuits installed on Kamoa-Kakula’s Phase 1 (left) and Phase 2 (right) concentrators. (Photo: Ivanhoe Mines)

A recent update on preliminary test work aimed at improving metal recovery at the Kamoa-Kakula copper operation in Democratic Republic of Congo noted that, while the output of the complex’s Phase 1 and 2 concentrators exceeded the nameplate recovery rate, the grade of copper in the mine’s tailings is still much higher than that of most major copper mines globally. Ivanhoe Mines’ Executive Co-chair Robert Friedland said, “We are leaving a significant amount of copper behind. If we can recover this copper, the production profile following the Phase 3 expansion could be in excess of 700,000 tons per annum. Not only would this provide additional revenue and cash flow, but also it would reduce even further our tailings footprint.”

Kamoa Copper S.A. is the operator of the Kamoa Copper Mining Complex and is a joint venture between Canadian mining company Ivanhoe Mines (39.6%), Zijin Mining Group (39.6%) and Hong Kong-based Crystal River Global Ltd. (0.8%). The Government of the Democratic Republic of Congo owns the remaining shareholding of the company (20%).

During 2022, the Kamoa-Kakula copper complex milled approximately 7.1 million metric tons (mt) of ore at an average feed grade of 5.5% copper, producing 333,497 mt of copper in concentrate. Based on the metallurgical recovery of 86% copper, which was in line with design parameters, more than 50,000 mt of copper was not recovered into concentrate and diverted to the tailings storage facility or used underground as backfill. The grade of Kamoa-Kakula’s tailings in 2022 averaged approximately 0.8% copper. For comparison, the average head grade of the copper mines globally was 0.6% in 2022, according to Bank of Montreal (BMO) research.

Friedland said that Kamoa-Kakula’s ore contains fine-grained copper sulphides (chalcocite), which to fully liberate from the host rock requires grinding of the ore to fine particle size. Grinding rock to increasingly finer particle size is exponentially energy intensive. During the original flowsheet development, a trade-off was struck between recovery and energy intensity. The Phase 1 and 2 concentrator design has primary grinding to 80% passing less than 53 microns (-53 μm) – a grind size significantly finer than most copper concentrators globally. Copper recoveries from the concentrators have improved year-to-date, averaging 87.1% during H1 2023, and periodically achieving as high as 90%. However, any further sustained improvement in copper recoveries presents a significant opportunity to generate additional revenue, according to Friedland.

Last year Kamoa Copper’s process engineering team, along with several external metallurgy specialists, initiated work to investigate ways to economically recover additional copper units from the tailings stream of the Phase 1 and 2 concentrators. To date, 13 workstreams with separate entities have been initiated leveraging various technologies to improve copper recoveries. Among the options being examined is the potential use of pulsed power technology to augment conventional crushing and grinding of ore. Pulsed-power is a technology that is claimed to release the power equivalent to the output of a nuclear reactor in a millionth of a second, and Ivanhoe has a vested interest in its success, along with mega-miner BHP.

Ivanhoe recently announced that it had converted an outstanding loan balance owed to it by I-Pulse Inc., a private US company that operates a pulsed power R&D facility in France, into an equity investment that gave it an investment position in I-Pulse valued at about $76 million along with certain investor rights including a right to maintain its percentage ownership in I-Pulse in the event of an equity financing. 

That investment announcement followed a December 2022 report by I-Pulse that it had forged a comprehensive collaboration arrangement with global miner BHP to identify and develop applications of pulsed-power technology across multiple aspects of the mining industry. 

Earlier in 2022, I-Pulse and Breakthrough Energy Ventures-Europe (BEV-E) had established I-ROX, a collaboration focused on demonstrating that short, high-intensity bursts of energy delivered using pulsed-power technology can quickly and efficiently shatter rocks and mineral ores. This process, which targets tensile weakness in rocks, could substantially reduce the time, energy usage and greenhouse gas (GHG) emissions currently generated by critical mining activities. The crushing and grinding of ores are the most energy- and capital-intensive aspect of the entire mining process, estimated to comprise approximately 4% of all electrical energy consumption globally and more than half a typical mine’s power usage.

BHP and I-ROX said they would work together to seek to accelerate the development of I-ROX’s technology and business, and BHP will be offered direct access to the technology. BHP has also made an equity investment in I-ROX, joining I-Pulse and BEV-E as shareholders.

In addition, BHP also made an equity investment in, and entered into a collaboration agreement with, I-Pulse to identify new applications for pulsed-power technology in a mining context. Within the mining industry, pulsed-power technology is currently deployed by I-Pulse’s former subsidiary, Ivanhoe Electric Inc., in mineral exploration via its proprietary Typhoon system. Further opportunities to develop and commercialize pulsed-power-based applications include drilling, tunnel boring, blasting and explosives replacement.

These collaboration arrangements, according to the companies involved, will link the mining and processing expertise of BHP with the pulsed-power technology and expertise of I-Pulse and I-ROX.

In the Kamoa-Kaklula update, Friedland also noted that promising preliminary results were received from work conducted by Expert Process Solutions (XPS) of Falconbridge, Canada. XPS has worked with Kamoa-Kakula since project inception, conducting metallurgical testwork during the study phases before construction. 

XPS was reappointed for a dedicated scope of work focused on grinding and reprocessing the tailings stream from the Phase 1 and 2 concentrators. Initial preliminary results indicate that with a feed grade of less than 1% copper, approximately 65% of the contained copper can be recovered from the tailings stream. The results generated a saleable concentrate with a grade of approximately 40% copper that could be processed on-site at the 500,000 mt/y direct-to-blister flash copper smelter that is currently under construction. For comparison, the copper concentrate grade from the Phase 1 and 2 concentrators is currently approximately 50%.

The test program consisted of fine-grinding the tailings stream to a particle size of 80% -12 μm, before conventional flotation, thickening and filtration.

Meanwhile, DRA Global of Johannesburg, South Africa, which also been working with Kamoa-Kakula since project inception, was appointed to design a process based on the initial metallurgical results. DRA conducted a desktop study on the construction of a dedicated, stand-alone processing plant to treat the entire tailings stream from the Phase 1 and 2 concentrators. The circuit design for the stand-alone processing plant uses conventional technology, such as high-intensity grinding mills and Jameson cells for the flotation, as well as additional thickening capacity.

Further metallurgical test work by XPS and engineering by DRA will continue to verify and optimize the process design, with the view to advancing the project to an investment decision.

The company said the other 12 workstreams will concurrently explore the most suitable option that will be implemented, such as conventional leaching, glycine leaching and ion exchange, in addition to pulsed power, among others.