en.Wedoany.com Reported - Gertrude Marape, head of the Physical Separation Division at Mintek, stated at Mintek's Platinum Group Metals Day that successfully rejecting coarse waste rock can reduce power demand in the milling circuit, decrease water consumption, and increase the feed grade of platinum group metals (PGMs). Through pre-concentration, the run-of-mine grade can double from 2 g/t to 4 g/t, significantly increasing the value of PGMs in the circuit.
In a case study presented, dense media separation (DMS) increased the PGM grade from 1.7 g/t to 4.8 g/t, with flotation losses of approximately 0.4 g/t. Marape noted that mining benefits include the ability to lower the cut-off grade, thereby increasing reserves and providing opportunities to extend mine life.
Mintek offers clients flexibility in their choices. Some clients already know the processes and technologies they require, while others ask Mintek for advice. Marape made these remarks while explaining the benefits of pre-concentration waste rejection and chromium recovery in PGM circuits. She was one of over a dozen Mintek managers, engineers, and scientists who presented at Mintek's auditorium. Mintek is a 92-year-old state-owned research institution located at 200 Malibongwe Drive, Randburg.
Although the typical PGM reefs are Merensky, UG2, and Platreef, Marape also focused on PGMs in chromitite layers, such as the Lower Group (LG) and Middle Group (MG) reefs, and of course the UG2 reef. Mintek has found that introducing a pre-concentration stage is easier in greenfield projects than in brownfield projects. While some brownfield projects are metallurgically suitable, implementation is often considered impractical.
Mintek provided information on recovering PGMs from chromium-rich MG and LG reefs, as well as from UG2 reef tailings. In work completed by Mintek, PGM losses in chromite concentrate ranged from 0.7 g/t to 0.8 g/t. The presentation also showed that chromium recovery could be significantly improved through secondary flotation.
Mintek's research indicates that the feasibility of pre-concentration depends on mineralogical characteristics. Sometimes it is effective, sometimes not, but when effective, it reduces capital and operating expenditures for the plant, lowers the cut-off grade, and provides flexibility when PGM extraction is suitable for mechanized or conventional mining methods. Marape stated that Mintek's experience with inter-stage chromium removal is that it offers higher yields and improved chromium recovery, but this comes with some PGM losses to the chromite concentrate.
PGMs and chromium can be recovered from MG, LG, and UG2 reefs, enhancing revenue potential. PGMs primarily originate from three branches of the Bushveld Igneous Complex—the Western, Eastern, and Northern limbs. While the typical reefs are Merensky, UG2, and Platreef, chromitite layers such as the LG and MG reefs also contain PGMs. Although LG and MG reefs were initially mined primarily for their chromium content, the PGMs in their tailings are also worth recovering.
Typical pre-concentration coarse waste rejection occurs after crushing and before milling. Most reefs contain significant pyroxene gangue, and rejecting this coarse waste can be achieved through dense media separation or dry sensor-based sorting, depending on which method is more advantageous, and also considering higher throughput. Mintek previously offered sensor-based sorters but now has partnerships with multiple sorting companies.
The purpose of coarse waste rejection is to discard waste rock. If the dense media separation option is chosen, Mintek will test whether the ore is suitable for pre-concentration via DMS; for clients opting for dry sorting, Mintek collaborates with several sorting companies. Mintek conducts testing primarily at laboratory and pilot scales to determine if the ore is amenable to pre-concentration via DMS, with the extent always depending on liberation.
Mintek's experience is that the technology is sometimes effective on UG2 and Merensky reefs, but ultimately depends on the degree of liberation. Mintek often advises clients to test different methods to determine which provides better pre-concentration results, with the goal of rejecting as much coarse waste as possible early on, without significant PGM losses. If coarse waste can be rejected, the benefit is minimizing waste discard before valuable material enters the processing plant.
