Tasman Metals' January 2015 prefeasibility study for the Norra Kärr rare earth deposit near Gränna, Sweden, designs a 1.15 Mt/a plant recovering 5,280 t/a of TREO under a zero-liquid-discharge policy.
The Prefeasibility Study NI 43-101 Technical Report for the Norra Kärr Rare Earth Element Deposit, Gränna, Sweden, was prepared for Tasman Metals Ltd with an effective date of January 13, 2015. GBM prepared the process design, based on testwork by WAI, JKTech, the Geological Survey of Finland, Dorfner ANZAPLAN and ANSTO Minerals. The report describes the design as preliminary and subject to change with further testwork. The plant combines crushing, rod and tower milling, magnetic separation to concentrate the eudialyte-bearing fraction, sulfuric acid leaching, impurity removal, solvent extraction and oxalate precipitation to a mixed rare earth oxide. It is built around a zero-liquid-discharge policy to limit the risk of water contamination.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Report effective date | January 13, 2015 | Not applicable | Prefeasibility study for Tasman Metals Ltd |
| Plant throughput | 1,150 | kt/a | Operates 24/7/365 |
| ROM grade | 0.6 | % TREO equivalent | Not applicable |
| Contained TREO | 6,910 | t/a | Not applicable |
| Recovered TREO | 5,280 | t/a | Not applicable |
| Overall recovery, Nd | 79.01 | % | Dy 78.78%, Y 72.92% |
| Overall recovery range by element | 72.92 (Y) to 79.44 (Eu) | % | Table 17-2 |
| Grinding | Open-circuit rod mill, tower mill on screen oversize | Not applicable | Not applicable |
| Beneficiation | LIMS, then wet high-gradient magnetic separation | Not applicable | Magnetic concentrate rich in aegirine and eudialyte |
| Product | Mixed rare earth oxide | Not applicable | Sent to a refinery for separation |
| Liquid discharge | Zero | Not applicable | Water treatment by lime, nanofiltration, RO and evaporation |
Overview
The plant treats 1,150 kt/a of ore at 0.6% TREO equivalent, containing 6,910 t/a of TREO, of which 5,280 t/a is recovered. Overall recoveries range by element from 72.92% for yttrium to 79.44% for europium, with neodymium at 79.01% and dysprosium at 78.78%. The final product is a calcined mixed rare earth oxide, which is packed and dispatched to a refinery for separation into individual metals.
Key Process Stages
Crushing. An apron feeder draws ore from the ROM bin onto a vibrating grizzly. Oversize goes to a jaw crusher, then the combined product passes a secondary screen and cone crusher and a tertiary screen with a tertiary crusher in closed circuit. Screen undersize goes to a fine ore bin, and all transfers are by conveyor.
Grinding. An open-circuit rod mill does the primary grinding. Its discharge is screened, the oversize goes to a tower mill, and the tower mill discharge returns to the same screen in closed circuit.
Magnetic beneficiation. Mill screen undersize passes a low-intensity magnetic separator to remove residual grinding media, then a wet high-gradient magnetic separator. This splits the feed into a magnetic concentrate enriched in aegirine and eudialyte and a non-magnetic stream depleted in iron-bearing minerals. The non-magnetic thickener underflow goes to tailings. The magnetic concentrate thickener underflow goes to leaching.
Leaching and impurity removal. Fresh sulfuric acid, plus acid recycled from solvent extraction, is added in the leach conditioning tank and in each leach tank to hold the pH set point. After leaching, magnesium oxide raises the pH to precipitate impurities, which are removed by thickening and filtration. The pregnant leach solution is then heated and reacidified for solvent extraction.
Solvent extraction and precipitation. Rare earths are extracted into an organic solvent, which is scrubbed with dilute sulfuric acid to remove impurities and stripped with oxalic acid. The insoluble rare earth oxalates are recovered by centrifugation and filtration, dried and calcined to a mixed oxide.
Water treatment. A bleed of raffinate is treated with lime, then by nanofiltration, reverse osmosis and thermal brine evaporation, so that dissolved metals do not build up and interfere with recovery. Gypsum sludge goes to tailings, permeate and condensate return to the raw water tank, and a solid salt residue, mainly magnesium and sodium sulfates, goes to a licensed storage facility.
Additional Interesting Data and Summary
The principal reagents are sulfuric acid, magnesium oxide, lime, oxalic acid, flocculant, a primary amine solvent, iso-decanol and Shellsol 2046. Sulfuric acid, magnesium oxide and lime are the three largest by volume. Sulfuric acid is to arrive by rail at the Tranås unloading facility and travel about 30 km by truck to site, and magnesium oxide is to be shipped from China via the Netherlands. The report notes that reagent consumption may vary with ore characteristics over the life of mine.
In summary, the 2015 Norra Kärr PFS concentrates the eudialyte-bearing magnetic fraction before acid leaching, recovers rare earths by solvent extraction and oxalate precipitation, and closes the water circuit completely, for about 79% recovery of the key magnet rare earths.
Key Processes
- Three-stage crushing
- Rod milling and tower milling in closed circuit with a screen
- Low-intensity and wet high-gradient magnetic separation
- Sulfuric acid leaching
- Magnesium oxide impurity precipitation
- Solvent extraction, scrubbing and oxalic acid stripping
- Oxalate precipitation and calcination to mixed rare earth oxide
- Zero-liquid-discharge water treatment
Source: Norra Kärr Project PFS, Gränna, Sweden, Prefeasibility Study – NI 43-101 Technical Report for the Norra Kärr Rare Earth Element Deposit, prepared for Tasman Metals Ltd, effective date January 13, 2015.
Earlier report summaries
Earlier versions of this profile, based on older technical reports, are retained below for source traceability. Dates and figures reflect each report’s own effective date and are superseded by the current information above.
Norra Kärr Project — 2012 Technical Report
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.
