ANSTO Test Work Lifts Korsnäs Rare Earth Extraction to 92% After Calcite Removal
European Resources' metallurgical collaboration with ANSTO Minerals has boosted magnet rare earth extraction at Korsnäs from 83% to 92% by removing calcite, highlighting a key processing lever for their Finnish rare earths project.
- Combined magnet rare earth extraction rises to 92% post-calcite removal
- Heavy rare earth extraction improves significantly, with terbium up 20 points
- Hydrochloric acid pre-leach increases TREY grade from 2.3% to 3.9%
- Physical calcite rejection via HGMS remains to be tested
- Pathway set for bench-scale mixed rare earth carbonate production
Significant Extraction Gains from Calcite Removal
European Resources Limited (ASX:ERE) has announced a marked improvement in rare earth element (REE) extraction from its Korsnäs project in Finland, following bench-scale test work by ANSTO Minerals. By introducing a hydrochloric acid pre-leach step to remove calcite before the established acid bake and water leach, combined magnet rare earth extraction climbed from 83% to 92%, with total rare earths plus yttrium (TREY) extraction rising from 86% to 93%. This uplift underscores calcite control as a pivotal factor in enhancing downstream processing performance.
Heavy Rare Earths See Material Improvement
The gains were most pronounced among the heavy rare earths, a critical subgroup for permanent magnet applications. Terbium extraction jumped by 20 percentage points to 69%, dysprosium by 23 points to 66%, and yttrium by 32 points to 75%. Light rare earths such as neodymium and praseodymium also improved, reaching extraction rates of 92% and 94%, respectively. ANSTO attributes these improvements partly to reduced formation of calcium sulphate phases like gypsum, which may otherwise trap rare earths or consume acid, although the exact mechanisms require further confirmation.
Hydrochloric Acid Pre-Leach Boosts TREY Grade
The hydrochloric acid pre-leach removed approximately 69% of calcite, nearly eliminating it from the feed and boosting the TREY grade from 2.3 wt% to 3.9 wt%. Remarkably, rare earth losses during this step were minimal, generally between 0-2%. The calcite removal effectively concentrates the valuable rare earths and reduces acid consumption in subsequent processing stages.
Exploring Physical Calcite Rejection Options
While chemical removal via acid pre-leaching has demonstrated clear benefits, European Resources is investigating physical calcite rejection methods to potentially reduce costs and acid usage. High-gradient magnetic separation (HGMS), a technique already proven by GTK-Mintec to upgrade hard-rock material from Korsnäs, is a leading candidate. Since calcite is non-magnetic, HGMS could selectively remove it before hydrometallurgical processing. However, the effectiveness of HGMS for calcite rejection in concentrate remains to be confirmed.
Towards a Bench-Scale Mixed Rare Earth Carbonate Product
The company plans to continue the ANSTO program by optimising extraction, impurity removal (notably aluminium, iron, silicon, uranium, and thorium), and precipitation steps. The goal is to produce a bench-scale mixed rare earth carbonate (MREC) sample, a standard intermediate product for downstream separation into individual rare earths. This work complements upstream beneficiation efforts under the REMHub program, which includes GTK-Mintec and the University of Oulu, aiming to integrate beneficiation and hydrometallurgical processes into a credible, cost-effective flowsheet.
Korsnäs Project Resource and Next Steps
The Korsnäs project hosts a 15.4 million tonne Inferred Mineral Resource at 1.00% TREO, reported in April 2026. The historical lanthanide concentrate tested by ANSTO is separate from this hard-rock resource. European Resources intends to apply the preferred processing route to fresh concentrate produced by REMHub's beneficiation program. Future work will also focus on optimising acid consumption and recycling, and further impurity removal to improve product purity and processing economics.
Bottom Line?
Calcite removal emerges as a crucial lever in Korsnäs rare earth processing, but the challenge now lies in scaling these gains cost-effectively and integrating physical separation methods to reduce chemical inputs.
Questions in the middle?
- Can physical calcite rejection via HGMS match or surpass chemical removal efficiency without significant rare earth losses?
- What are the cost implications of acid consumption and recycling in the calcite removal process at scale?
- How effectively can impurity removal (e.g., uranium, thorium) be integrated to produce a market-ready MREC product?
