Additional metallurgical test work on London-listed Blencowe Resources’ Orom-Cross graphite project, in northern Uganda, has been completed by technical specialist firm IMO based in Perth, Australia.
Blencowe said on December 6 that the objectives of the test work had been met or exceeded in this latest round of test work.
The test work was critical to understanding the quality of the end-product that Orom-Cross can deliver as a high-grade graphite concentrate, as well as what the process flow will look like to achieve this on a precommercial scale. Blencowe said the work also provided a significantly greater quantum of end-product for end-user testing, which is critical for the definitive feasibility study (DFS).
Blencowe appointed IMO to undertake metallurgical test work on material gathered from its drilling campaigns, which covered both the Northern Syncline and Camp lode areas within Orom-Cross. The programme was designed to deliver on several objectives.
Among the objectives was the need to confirm whether a 95% to 97% total graphite content pure concentrate is possible with low impurities of thorium and vanadium.
The aim is also to confirm whether about 90% recovery is achievable for this concentrate, and to confirm the liberation process to maintain a high percentage of “jumbo/extra-large/large” flakes within the concentrate.
The aim is also to confirm the process flow diagram for plant design as part of the DFS. The delivery of the bulk concentrate samples will also allow Blencowe to initiate discussions with potential offtake partners.
"These IMO-met test results . . . not only continue to underpin Orom-Cross concentrate as high quality in all key areas relevant to end-users but the test work has highlighted that we can now deliver these end results on a much greater scale of raw material as processed. This is a key step towards commercial-stage production testing in a pilot plant facility,” Blencowe executive chairperson Cameron Pearce said.
Open cycle flotation testing produced recoveries of between 90% and 92%, with concentrate grades consistently ranging between 95% and 98%, which are battery grade.
The additional metallurgical test work was commissioned to test the upgradeability of the bench scale test work completed by testing company SGS in Lakefield, Canada.
A total of 1 400 kg was processed this time, compared with 100 kg within the SGS test work, with all metallurgical test work undertaken to date showing a robust flowsheet capable of repeatable metallurgy for a range of feed samples from Orom-Cross, Blencowe stated.
A total of eight rougher and cleaner flotation tests were carried out on the master composite that culminated in a flowsheet that is atypical of similar graphite projects.
The flowsheet consists of a flash and rougher flotation stage, followed by a primary cleaning circuit with a polishing mill, followed thereafter by three stages of cleaner flotation. The intermediate concentrate is classified and then further upgraded in secondary cleaning circuits with stirred media mills, followed by cleaner flotation.
The proposed flowsheet was employed in a continuous pilot operation to determine the metallurgical response under typical operating conditions. The final concentrate was graded at 96.4% C(t) at 90.6% total carbon recovery, which exceeded the company's expectations and places the end-product recovered at the higher end of the spectrum in comparison to its peers.
Test work was focussed on achieving the stated objectives, Blencowe said, and was not geared towards optimising the flake size fractions. As the resultant splits using an unoptimised circuit were within 5% of the fractions as determined by the original SGS bench scale works, there may be further incremental value to be added by optimising ahead, the company said.
“It also highlights the potential to increase the percentage of the more valuable coarse flake products through further optimisation of the processing circuits, and this will be considered in the next round of testing,” Pearce said.
Blencowe said the key takeaway from these results was that the scaling factors in the metallurgical testing would likely replicate the original test work and results through to commercial scale production.
At the end of this larger-scale metallurgical programme, about 80 kg of concentrate was produced, compared with the 5 kg to 8 kg produced from SGS, which will be forwarded to potential end-users and project partners for additional test work on screening splits and grade analysis, as well as suitability for further downstream processing of the concentrate.
The design of the processing plant will be based on both the SGS and IMO test work and best practice in similar operations.
Importantly, the process requires no primary crushing or grinding of the ore, thereby preserving the larger flake sizes, which is a material advantage over hard-rock graphite deposits.
“This latest set of results sets us up nicely for the bulk sample trial we will be conducting on 100 t of Orom-Cross composite in the first half of 2023, and if these same results are produced from that exercise, we will be largely prequalified in terms of end products delivered as concentrate," Pearce said.