Deep Fox and Foxtrot PEA Pairs a Labrador Magnetic Separation Plant With an Acid Bake and Water Leach Refinery for Mixed Rare Earth Carbonate

Search Minerals' 2022 technical report for the Deep Fox and Foxtrot rare earth project in southeastern Labrador concentrates 730,000 t a year of ore by LIMS and WHIMS. The WHIMS concentrate is shipped to a hydrometallurgical plant on the island of Newfoundland.

The Technical Report on the Deep Fox and Foxtrot Project, Newfoundland and Labrador, Canada, was prepared by SLR Consulting (Canada) for Search Minerals Inc., with an effective date of December 31, 2021 and a signature date of July 18, 2022. Its recovery methods section is based on NewPro Consulting & Engineering Services' processing plant scoping study update (Revision C, January 25, 2022), with minor edits. Ore is beneficiated by physical separation at a Primary Production Plant near the deposits in Labrador. The concentrate is processed at a Hydrometallurgical Processing Plant at a brownfield site in Newfoundland near reagents and power, where the precipitate is made. The site for that plant had not yet been selected.

Critical Data

Overview

At the Primary Production Plant, run-of-mine ore is jaw crushed and ground in a SAG mill and ball mill. Low-intensity magnetic separation (LIMS) first removes magnetite and maghemite, and wet high-intensity magnetic separation (WHIMS) then produces the REE concentrate. The concentrate is shipped in bulk carriers during the eight-month open water season. At the Hydrometallurgical Processing Plant, the concentrate is acid baked and water leached. Iron, thorium and aluminium are removed by precipitation, and the REE are precipitated as an intermediate. That intermediate is re-leached and purified by ion exchange, solvent extraction and further precipitation steps before final carbonate precipitation.

Key Process Stages

Crushing and grinding. Ore is loaded by front-end loader into a 100 t live ROM bin, about 66 minutes of surge. A vibrating grizzly feeds the jaw crusher, which runs about 19.4 h/d. A belt magnet protects the SAG mill feed conveyor, and the ball mill cyclones classify to P80 53 µm.

Magnetic separation and concentrate handling. A LIMS rougher-cleaner circuit makes a ferromagnetic concentrate that may be saleable, though this is not considered in the PEA. LIMS tails go to WHIMS. WHIMS concentrate is thickened and filtered and stored in a 100,000 t shed, which holds 202 days of production. It is shipped in carriers of up to 15,000 t. Tailings are thickened, filtered and trucked to a TSF next to the plant.

Acid bake. Concentrate is mixed with 256 kg/t sulphuric acid in a pug mill, with a standby unit because of the high wear. It is then baked at 215°C for 150 minutes in an indirectly diesel-fired kiln. Kiln off-gas is scrubbed with magnesium carbonate slurry. About 93% of the Pr, Nd and other light REE, and of Tb and Dy, are made water soluble. Heavy REE sulphation is lower, about 65% for Lu.

Water leach and impurity removal. Six leach tanks at about 20% solids and 90°C give 24 hours, with residual acid controlled to 8 g/L. Four impurity removal tanks at 90°C give two hours, with magnesium carbonate raising the pH to 3.9. This precipitates 100% of the Fe, 92% of the Th, 60% of the Al and 16% of the U, with about 2% of the key REE. The residue is thickened and washed on a horizontal belt filter.

First REE precipitation and releach. Sodium carbonate at pH 6.5 and 50°C precipitates nearly all REE, Al and Fe. The precipitate is re-leached with sulphuric acid at pH 1.0. Magnesium carbonate at pH 3.5 then removes residual silica and iron.

Purification. A continuous counter-current ion exchange (CCIX) system with amine-functionalized resin removes uranium. A pulsed-column SX circuit with 1% Primene JMT removes 99.7% of the thorium. Zinc and lead are precipitated at pH 3 with hydrogen sulphide at 45°C. Aluminium is precipitated at pH 5.0 to 5.2, and that precipitate is recycled to the water leach because REE co-precipitate with it.

REE carbonate. Sodium carbonate at pH 6.0 and 30°C precipitates the hydrated REE carbonate. It is thickened, filtered, dried, bagged and containerized for shipment to a refiner.

Tailings. Uranium and thorium strip liquors are combined with the leach residue. Phosphate and lime are added to precipitate and stabilize dissolved species, and the solids go to a dry-stack tailings system.

Additional Interesting Data and Summary

The report states that further testwork is needed on flocculant types for low-pH duties, on uranium and thorium removal conditions, and on ways to limit aluminium extraction and REE co-precipitation. The Labrador concentrator assumes an upgraded existing dock at Fox Harbour (St. Lewis), while port alternatives were being assessed.

In summary, the 2022 Deep Fox and Foxtrot report splits processing between a small magnetic separation concentrator in Labrador and a sulphuric acid bake and water leach refinery in Newfoundland. The refinery produces a purified mixed rare earth carbonate.

Key Processes

• Jaw crushing, SAG and ball milling to P80 53 µm
• LIMS removal of magnetite and WHIMS concentration of REE minerals
• Filtered tailings to a TSF
• Sulphuric acid bake in a kiln and water leaching
• Impurity removal with magnesium carbonate
• REE precipitation and re-leaching
• Uranium ion exchange and thorium solvent extraction
• Zinc sulphide and aluminium precipitation
• Mixed REE carbonate precipitation and drying

Source: Technical Report on the Deep Fox and Foxtrot Project, Newfoundland and Labrador, Canada, prepared by SLR Consulting (Canada) Ltd. for Search Minerals Inc., effective date December 31, 2021.