Beneficiation – Ore Sorting
Ore sorting is the proposed technology to produce a bastnaesite concentrate from the North T ore body. Ore sorting involves the separation of the bastnaesite mineralisation from the quartz gangue using X-Ray Transmission (XRT) technology. This sensor was deemed suitable due to the significant differences in atomic density between bastnaesite and quartz.
Ore sample from North T Zone showing red bastnaesite crystals with quartz waste.
TOMRA Sorting Mining (TOMRA) engineers conducted a Performance Test at Saskatchewan Research Council (SRC) on three sets of samples to determine whether TOMRA products are capable of sorting bastnaesite from quartz. The material was pre-screened into the size fractions: 8-20mm, 20-30mm and 30-60mm. Oversize was crushed further, while the undersized fraction was retained for gravity testwork.
TOMRA COM Tertiary XRT Ore Sorter used in the ore sorting Performance Test at the SRC.
Results
For training of the COM Tertiary XRT, a sample sheet of rocks with varying bastnaesite mineralisation was set up. The sorting of ore is made simple by the fact that the bastnaesite has a very high atomic density whilst the gangue, which is quartz, is very low atomic density. The colour pixels, as shown in Figure 5, are assessed as a percentage of the single rock area with that percentage then used for the sorting purpose.
Sample Sheet for COM Tertiary XRT training purposes.
Each size range was tested at three different settings of reject vs product. The testwork showed that a 36% REO product could be produced from feed containing 10.5% REO at a REO recovery of 70%. Products with REO up to 41% were produced along with REO recoveries up to 87% and upgrade factors up to 5. REO in the waste stream was reduced to 1.7% with corresponding REO loss down to 13%.
In all the tests, the material was fed through a single time with no cleaning or scavenging carrying out on product or reject. Since the ore sorting equipment has a large capacity compared to the throughput for plant requirements, an installed ore sorter will be flexible and used in a number of different modes to produce a high grade bastnaesite product to be transported for downstream processing.
Gravity Testwork on Fines
Spiral testwork and shaking table testwork was undertaken on the fine material. Shaking table testwork proved that an upgrade of over four times to 40% REO product at an REO recovery of 80% could be achieved, producing product and rejects as shown below:
A high grade REO concentrate and corresponding reject sample from one of the shaker table runs.
Conclusions and Next Steps
Beneficiation of the Nechalacho T-Zone Bastnaesite mineralised section was successfully tested by sorting into a high grade bastnaesite product containing up to 40% REO and a reject material using a Tomra COM XRT Ore sorter. The ore sorting process has sufficient flexibility to produce a high grade product from similar feed materials. Additionally, at lower ore grades, the ore sorter will produce similar results due to the grain size of the mineralisation vs the particle size that can be sorted through the sorter. Fines produced in the mining, crushing and screening stage can also be processed to produce a high grade bastnaesite utilising shaking tables, thereby increasing overall REO recovery.
The successful testwork demonstrates that it is possible to produce a high grade REO product from ore from the North T Zone. This is confirmation that the North T Zone is the ideal focus for the establishment of a near term operation.
In addition to this concentration work, leaching testwork has also been underway. The testwork aims to confirm that rare earths are able to be leached from a high grade concentrate into a solution, from which a high purity mixed rare earth product will be produced. An announcement on the results of this work will be made as they are available.
Investigative Leaching Testwork
Vital Metals Limited and it’s subsidiary Cheetah Resources Pty Ltd has successfully completed leaching testwork on high grade concentrate from the North T deposit at its Nechalacho Rare Earth project. The purpose of this testwork was to confirm the amenability of leaching rare earths contained within concentrate produced by ore sorting via recognised process flowsheets for the treatment of bastnaesite.
Leach Feed Mineralogy and Assays
High grade bastnaesite samples (~50% REO) were selected from the North T-Zone (shown in Figure 1) of the Nechalacho Rare Earth project. The North T¬ zone is the same zone from which samples were used to undertake ore sorting and gravity beneficiation testwork at SRC and as announced on 5th December 2019.
Figure 1: Location of North T Zone
Testwork was conducted on a 90% ‘Bastnaesite’:10% Quartz to simulate a leach feed anticipated by the product from the ore sorter. Leach feed was thus approximately 45% REO, 20% SiO2 and 10% CaO.
Leaching processes using Hydrochloric acid and Sulphuric acid have both been tested to find the most suitable and optimal process route. High neodymium leach recoveries (where neodymium is indicative of overall rare earth) up to 97% in sulphuric acid media and up to 93% in hydrochloric acid media were achieved. Of particular interest is the potential to selectively extract cerium depending on customer requirements.
Leach optimisation and rare earth recovery from the leach liquors testwork is now being undertaken to fully develop the process flowsheet and develop rare earth precipitate specifications.
Testwork conducted by both SGS Lakefield and SRC demonstrates that North T-Zone concentrate, similar to that produced during beneficiation testwork, is amenable to leaching via either hydrochloric acid or sulfuric acid with REO recoveries of up to 97%.
These results provide Vital the confidence to proceed with a target of establishing a near-term demonstration scale operation, focussing on the North T deposit at the Nechalacho rare earth project.
Optimisation and rare earth recovery work including purification testwork is currently underway to confirm a product specification and samples for supply to prospective customers.
Vital is also focusing on developing capital and operating cost estimates, along with development timelines.
