Initial diagnostic leach testing of ionic clay material from Axel REE’s (ASX: AXL) Caladão rare earth elements and gallium project in Brazil has confirmed the material will perform as expected under in situ recovery (ISR) conditions.
Column leach test work on mineralised weathering-profile material from the 128-million-tonne Woolrich deposit returned soluble total rare earth oxide results ranging from 443 parts per million to 546ppm.
It also defined optimal low-acidity base-case conditions that are being applied to further testing.
Axel is using the results to define the operating window for column leach testing and future field-scale ISR trials, as well as to supporti the development of a direct ISR pathway using magnesium sulphate leaching and inform hydraulic control and monitoring strategies.
PLS Breakthrough Achieved
The first two columns (CLT-01 and CLT-02) achieved a pregnant liquor solution (PLS) breakthrough to validate the hydraulic behaviour of Woolrich material under ISR-analogous conditions.
The columns were loaded with Woolrich material and operated with magnesium sulphate as the leach solution (or lixiviant)—the same low-cost, low-toxicity reagent proposed for Axel’s full-scale ISR concept at Caladão.
Early kinetic observations indicated CLT-02—which was operating at the lower reagent concentration—progressed through the column more rapidly, consistent with the diagnostic leach finding that extraction performance is not highly sensitive to reagent strength.
Moisture content tracked consistently in both columns, with flow rates optimised during operation.
Testing on columns CLT-03 and CLT-04 will commence once initial leach performance data from CLT-01 and CLT-02 has been reviewed and incorporated into the next-stage test design.
Critical ISR Milestone
Column leach test work represents a critical milestone in Axel’s ISR development strategy for the Caladão project.
The strategy is focused on identifying priority wellfields at the Woolrich deposit for field trials, ahead of a pilot plant and subsequent modular expansion.
The work simulates the percolation leaching process at a larger scale and under more representative conditions than bench-scale bottle roll tests, providing a number of key data.
These include inputs for leach kinetics and rare earth recovery curves over extended timeframes, reagent consumption rates and optimisation of lixiviant concentration, impurity co-extraction profiles and downstream processing requirements, and engineering design parameters for wellfield layout and ISR field trial planning.
Gallium Leach Tests
Axel has commissioned the first three leach tests in a separate program to evaluate acid leach conditions for gallium extraction from Caladão material.
Gallium has been subject to Chinese export restrictions since 2023 and is a critical input for semi-conductors and defence electronics.
Caladão’s 439Mt gallium resource is considered to be one of world’s largest discrete gallium inventories and positions Axel as a potential non-Chinese producer.
“Combined with the strong diagnostic leach results already in hand, we are building a robust technical foundation to support a low-capital, modular ISR development concept—a scalable pathway to bringing Caladão’s magnet-rich rare earth system into production, as a critical minerals supply chain solution for OEMs and governments seeking alternatives to Chinese sources,” non-executive chair Paul Dickson said.
