Metals miner Ivanhoe Mines has announced “highly promising” preliminary testwork for improving copper recoveries at its Kamoa-Kakula copper mine in Kolwezi, in the Democratic Republic of Congo.

Results show a significant improvement in total recoveries can be achieved by liberating copper from a tailings stream, the Canada-headquartered company says.

Based on these results, Kamoa-Kakula can further increase production, revenues and cash flow.

“Despite the Phase 1 and 2 concentrators exceeding the nameplate recovery rate, the grade of copper in Kamoa-Kakula’s tailings is still much higher than that of most major copper mines globally.

“This is a direct consequence of Kamoa-Kakula being the highest-grade major copper mine globally. However, we are leaving a significant amount of copper behind, which this planet so desperately needs right now for our energy transition,” states Ivanhoe founder and executive co-chairperson Robert Friedland.

“If we can recover this copper, the production profile following the Phase 3 expansion could be in excess of 700 000 t/y. Not only would this provide additional revenue and cash flow, but it would also reduce even further our tailings footprint.

“We are targeting total copper recoveries in the mid-nineties from this breakthrough, as well as from the other concurrent workstreams. Our experienced team, with a proven record of execution and delivery, is leaving no stone unturned to improve the efficiency of extraction from this incredible endowment,” he adds. 

Last year, Kamoa Copper’s process engineering team, together with a number of internationally recognised 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. 

The Kamoa-Kakula Copper Complex last year milled about 7.1-million tonnes of ore at an average feed grade of 5.5% copper, producing 333 497 t of copper in concentrate.

Based on the metallurgical recovery of 86% copper, which was in line with design parameters, in excess of 50 000 t 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 last year averaged about 0.8% copper. For comparison, the average head grade of copper mines globally was 0.6% last year, according to business service provider Bank of Montreal research.

Kamoa-Kakula’s ore contains fine-grained copper sulphides (chalcocite), which requires grinding of the ore to a fine particle size to fully liberate from the host rock.

Ivanhoe points out that grinding rock to an ever-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 μm. This grind size is already significantly finer than most copper concentrators globally.  

Copper recoveries from the Phase 1 and 2 concentrators have improved year-to-date, averaging 87.1% during the first half of this year, and periodically achieving as high as 90%.

Any further sustained improvement in copper recoveries, however, presents a significant opportunity to generate additional revenue at Kamoa-Kakula.

To date, 13 workstreams with separate entities have been initiated leveraging various technologies to improve copper recoveries. This includes the recently announced collaboration with cloud-based solutions provider I-Pulse.

More recently, promising preliminary results were received from work conducted by Canadian testing services provider Expert Process Solutions (XPS).

XPS has worked with Kamoa-Kakula since project inception, conducting metallurgical testwork during the study phases before construction. Therefore, XPS has a high degree of experience working with both the Kamoa and Kakula deposits. 

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, about 65% of the contained copper can be recovered from the tailings stream.

The results generated a saleable concentrate with a grade of about 40% copper that could be processed on site at the 500 000 t/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 about 50%. 

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

IMPROVED ECONOMICS

Engineering consultant DRA Global, a company that has 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, standalone processing plant to treat the entire tailings stream from the Phase 1 and 2 concentrators.

The circuit design for the standalone processing plant uses conventional technology, such as high-intensity grinding mills and Jameson cells (diverisifed miner Glencore-owned technology) for the flotation, as well as additional thickening capacity. 

Ivanhoe adds that DRA has also determined preliminary, high-level capital expenditure and operating costs associated with the construction and operation of the tailings recovery plant, and the economics are significantly positive. 

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

“Concurrently, the other 12 workstreams will continue to explore the most suitable option that will be implemented. The workstreams, among others, consist of conventional leaching, glycine leaching, ion exchange, as well as pulsed-power technology by I-Pulse to crush rock.

“Pulsed power technology consists of high-intensity bursts of electrical energy that can quickly and efficiently shatter rocks and mineral ores by targeting the tensile weakness of rocks,” the company says.