This report presents a conceptual processing flowsheet for rare earth element, yttrium, and zirconium recovery from the Norra Kärr deposit, supported by test work and scoping-level cost estimates.
Report context
Dated May 11, 2012, this technical report for the Norra Kärr Project describes a conceptual recovery method for rare earth elements (REEs), yttrium, and zirconium. The project is owned by Tasman Metals Limited. The processing approach is based on test work completed by SGS-Lakefield of Ontario, Canada, the Geological Survey of Finland (GTK), and bench test work by J.E. Litz and Associates, LLC of Golden, Colorado, USA. Test work was conducted in phases from early 2011 through February 2012.
Processing route
Process mineralogy
The peralkaline intrusive rocks hosting REE-Y-Zr mineralization at Norra Kärr are geochemically enriched in sodium, potassium, and alumina, primarily contained in gangue minerals including natrolite, nepheline, analcime, sodium amphiboles, plagioclase feldspar, potassium feldspar, and acmite. The presence of these readily acid-soluble sodium silicate gangue minerals significantly limits processing options. Beneficiation methods are being investigated to improve feed material quality for the acid leach stage.
Flotation is being tested to lower the amount of sodium-bearing aluminosilicates (feldspar and nepheline). Because the primary ore mineral eudialyte is paramagnetic, magnetic separation is being tested to reject the sodium-bearing clinopyroxene aegirine before the acid leach stage. The other important REE-bearing mineral, catapleiite, reports to the magnetic concentrate. Test work indicates that tailings generated by flotation and magnetic separation can reduce the original feed material volume by 25 to 35 percent. The float product, rich in Na-K and Al, may provide an alternate feed to ceramic, glass, or abrasive manufacturers.
Comminution and beneficiation
The conceptual flowsheet envisions sequential extraction and recovery of REEs by comminution of the ore, beneficiation of the ground feed to remove acid-consuming minerals, and hydrometallurgy to separate and extract values. Ore is crushed and ground. The ground ore is deslimed at about 25 µm particle size, and the coarse fraction is subjected to flotation to remove gangue minerals high in alumina and sodium (feldspar and nepheline). The flotation tailings and slimes then are subjected to magnetic separation. Test work by the GTK showed that the magnetic fraction contains greater than 80 percent of the rare earth elements, greater than 85 percent of the yttrium, and approximately 60 percent of the zirconium.
Acid leaching
The magnetic concentrate is leached with sulfuric acid. The acid leach dissolves the REE-Y-Zr values concomitantly with major amounts of sodium, iron, and aluminum. The high sulfate level causes the REEs to crystallize as sulfate double salts. The leach slurry is diluted with water to dissolve the double salts, then thickened and filtered. The filter cake reports to solid tailings, and the filtrate advances to metals recovery.
Metals recovery
The REEs dissolved in the leach filtrate are precipitated as double salts (RE₂(SO₄)₃·Na₂SO₄·H₂O). Because the rare earth double salts have very low solubility above approximately 20 g/L concentration of sodium sulfate, additional sodium sulfate is added to about 30 g/L. The double salts are thickened, filtered, and rinsed. The double salt filter cake is dissolved in water, and sodium carbonate is added to re-precipitate the REEs as carbonates. The carbonates are thickened, filtered, and dried.
The mother liquor from the double salt precipitation advances to an amine solvent extraction to recover yttrium. Because the mother liquor remains acidic, it favors yttrium recovery, which has a much higher distribution coefficient into amines at high acid conditions than zirconium. The yttrium-amine then is stripped with a hydrochloric acid and sodium chloride mixture. In the current design, the Y-rich solution advances to the carbonate reactor where it is mixed with the filtrate from the REE water leach. With addition of Na₂CO₃, a mixed RE+Y carbonate is precipitated, then thickened, filtered, dried, and prepared for shipment.
The raffinate from yttrium extraction advances to zirconium solvent extraction. The solution pH is raised to about 2.0 by addition of sodium carbonate, and the zirconium is extracted by an amine. The zirconium then is stripped with a hydrochloric acid–sodium chloride mixture and precipitated from the strip solution by addition of sodium carbonate. The zirconium carbonate is thickened, filtered, and dried.
The report notes that this flowsheet may be modified to produce a separate Y-carbonate concentrate.
Salable products
At present, two salable products are envisioned: a mixed rare earth element–yttrium carbonate product and a zirconium carbonate product. Future test work may evaluate production of yttrium carbonate as a separate co-product.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Ore feed rate (annual) | 1,500,000 tonnes per year | Conceptual design (PEA) |
| Feed rate (hourly) | 167 tonnes per hour | Conceptual design (PEA) |
| Annual operating hours | 8,400 hours | Conceptual design (PEA) |
| Grinding target size | Approximately 90 microns | Conceptual design |
| Desliming size | About 25 µm | Conceptual design |
| Volume reduction by beneficiation | 25–35 percent | Test work (GTK) |
| REE recovery to magnetic concentrate | >80 percent | Test work (GTK) |
| Y recovery to magnetic concentrate | >85 percent | Test work (GTK) |
| Zr recovery to magnetic concentrate | Approximately 60 percent | Test work (GTK) |
| Plant operating cost | US$41.48 per tonne milled | Scoping estimate (±35%) |
| Power rate | US$100 per MWh | Scoping estimate |
| Process water rate | US$0.25 per cubic meter | Scoping estimate |
| Sulfuric acid consumption | 14.3 tonnes per hour | Scoping estimate |
| Sodium carbonate consumption | 6.7 tonnes per hour | Scoping estimate |
Project website: https://ejatlas.org/print/norra-karr-norra-karr-sweden-mining-conflict
Technical qualifications
This report presents a conceptual process and flowsheet that is based on generally known metallurgical and chemical principles. The scoping level operating cost estimates carry an uncertainty of plus or minus 35 percent. The beneficiation portion of the flowsheet (flotation and magnetic separation) was developed during five months of test work by the GTK, with results given in an internal report dated January 12, 2012. The first leach tests on whole ore samples were conducted by Lakefield in early 2011, but this work was subsequently stopped to allow for beneficiation work; there is no comprehensive report from Lakefield. More detailed equipment specifications, capacities, and prices will be included in a pending prefeasibility study and feasibility study on the project. The report acknowledges significant fresh water requirements and a large effluent stream, with treatment challenges due to high levels of aluminum, iron, sodium, sulfate, and chloride.
Source: Tasman Metals Limited, Norra Kärr Project – 2012 Technical Report, Pincock, Allen & Holt, May 11, 2012, Section 17.0 Recovery Methods.
