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MEI Online: Commodities: Metallic Ores: Rare Earths & Thorium: Latest News: December 6th 2013
:: Significant Advance in the Treatment of Radionuclides in Rare Earth Mining
Rare Element Resources which is advancing development of the Bear Lodge rare earth project has had its pilot plant test program, conducted at SGS Lakefield Canada, validate the significant benefits of its proprietary processing technology and identified the opportunity for additional project improvements. It was “an unqualified success not only in demonstrating on a larger scale the process benefits in the critical metrics of achieving high bulk concentrate purity, excellent recoveries and substantially reducing reagent costs but also in identifying additional opportunities for improved efficiencies and cost savings," said Jaye Pickarts, COO.
“The testing also confirmed the effectiveness of an innovative process to isolate the thorium and uranium, which are usually associated with rare earth deposits, making for safe, controlled disposal. Equally significant, it was recognised that because of the purity of the concentrate, downstream elemental separation should be evaluated for the additional value it could bring to the project. We will begin work on evaluating the technology alternatives for separation and assessing end-user needs to determine the most attractive product mix."
The test work confirmed the following key advancements:
Activities in support of the upcoming feasibility study began in mid-2013, with the start of the pilot plant test program and several engineering-related trade-off studies. Along with the advantages of the company’s proprietary processes, pilot plant testing and engineering trade-off studies identified a possible modification to the PUG process that, if proven successful, would significantly reduce capital and operating costs without significantly impacting recoveries. Engineering and bench-scale testing will begin immediately on this potential change with additional pilot plant studies anticipated in early 2014. To ensure consideration of the results of this work and the multiple trade-off studies undertaken by the company over the last six months, as well as the results of the recent drill campaigns, the detailed design and economic analysis portion of the feasibility study is now expected to start in the first half of 2014.
As currently proposed, mined ores would be beneficiated using some combination of crushing, screening, gravity and magnetic separation at a PUG plant to be located adjacent to the mine. During pilot plant testing, the developed PUG flowsheet was optimised to reduce feed mass from Bull Hill ore by 20% and from Whitetail ore by 45%. This resulted in a final PUG concentrate with average REE recoveries of 95% and 86%, respectively.
The resulting mineral pre-concentrate was then subjected to the hydromet process which employs a hot chloride solution to extract the REEs into a pregnant leach solution (PLS). Using closed reactor vessels, the PLS reacted with oxalate reagents under optimised conditions to facilitate selective precipitation of REEs with impurities remaining in solution. During testing, some 97% of total REEs were selectively separated in the oxalate precipitation process, with 98-99% of the total base metals and silica remaining in the barren solution. Because of the base metal concentration, it should be possible using a crystallization acid distillation process to beneficiate base metals separately. The potential value of these byproducts will be evaluated.
A significant amount of HCl remained in the PLS. Testing confirmed that at elevated temperatures, the addition of oxalic acid helped to generate HCl after precipitation of the REEs. As a result, the waste solution had a significant amount of free acid and water that was recoverable. About 80% of total free acid was recovered by distillation and re-constituted through a rectifier as azeotropic HCl (20% strength). This is expected to result in a 50% reduction in required fresh HCl at the leach step. Water recycling of between 80 to 90% was accomplished, which would significantly reduce fresh water needs as well.
During the acid digestion portion of the process, between 82 and 90% of the total Th and low level U associated with the ore was digested along with the REEs and subsequently transferred to the PLS. This resulted in a leach residue, with Th and U concentrations significantly lower than background that could be disposed of safely in a controlled tailings storage facility.
As the PLS continues through oxalate precipitation, the REEs and Th are sequestered in a bulk oxalate precipitate, leaving base metal impurities and U in the now barren PLS. The next step in the process recovers significant amounts of oxalate and acid reagents from the barren PLS by crystallisation, reducing raw materials costs, while the base metals and U remained in the final distillation residue. They can be treated further for potential economic recovery or disposed of in a tailings storage facility.
The new Provisional Patent applies to the innovative process where all Th is selectively removed from the REE concentrate, resulting in a 97% pure final bulk concentrate product. At this stage, additional oxalate reagents are also recovered, further improving the economics of the project. The Th could then be transferred to an off-site licensed disposal facility.
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