Quest Rare Minerals, which owns the Strange Lake rare earth deposit in northern Quebec, recently held a tour of its mini-pilot plant at Process Research Ortech in Mississauga, ON, where it’s testing the solvent extraction circuit before ramping up to a full scale program.
In a Jan. 31 presentation, the firm explained how the mini-program will process a small sample of ore from Strange Lake’s high grade B zone to confirm the previously defined flow sheets to extract zirconium, niobium, uranium, thorium and rare earth concentrate. Quest started working on the flow sheets at Ortech in early 2012.
While the junior intends to scale up the operation shortly, Quest’s VP of operations Colin Lindsay says the purpose of the mini-program is to “iron out the wrinkles” before trucking down and consuming larger quantities of sample.
The current program will mainly test if the organic reagents used in the solvent extractions could be recycled without degeneration or clogging up the circuit with residue, Lindsay says, explaining organic reagents are oil-based and particularly selective at picking out the metals of interest in an aqueous solution.
“So what you are doing effectively is mixing oil and water … You mix it up in an emulsion and it looks a bit like salad dressing. The valuable metals will transfer over to the organic phase and the aqueous phase is diluted. Then you have to strip the metals out of the organic, which goes back to the aqueous solution,” he says.
But the first step is getting the material from the mine in the solution before separating the metals, says Mike Robart, Quest’s process metallurgist, adding most of the front end development work has been completed by Colorado-based Hazen Research.
These initial steps include grinding the crushed ore prior to mixing it with sulphuric acid. Once mixed, the wet, brownish-grey material is heated in a kiln, where the acid breaks down the material to produce metal sulphates, which are readily soluble in water. The excess acid is recovered and recycled.
The material, now dry and greyish-white in colour, is leached and then filtered and washed to form a pregnant leach solution containing the desired metals, with zirconium being the first in line to be extracted. Once the zirconium solvent is isolated it is neutralized to produce zirconium oxide product.
During the site visit, Quest demonstrated how zirconium oxide is produced via the aforementioned steps, without specifying the reagents. Once the zirconium solvent circuit has been operating for some time, Robart says the downstream steps of extracting niobium solvent and rare earth oxalate will be included, noting both have been defined at bench scale with over 90% recoveries.
Niobium solvent is extracted after adjusting the pH levels of the remaining solution and then converted into niobium oxide. Following that, uranium and thorium are removed and disposed and oxalic acid is added to create rare earth element and yttrium precipitate, which is re-dissolved to form a solution of rare earths and yttrium that could be further separated.
The results from the mini-program will be incorporated in Strange Lake’s prefeasibility study, expected out in late March. The cost to run the mini-pilot plant is roughly $250,000 a month.
Quest closed Feb. 8 down 2.5% at 96.5¢ in Toronto.
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