Mixed Rare Earth Carbonate and Titanium Products from Anatase-Bearing Feed at the Tiros Project

A look at the process design in the preliminary economic assessment for Resouro Strategic Metals' Tiros rare earths and titanium project in Brazil, covering the two main processing routes for coarse and fine material.

The Tiros Rare Earths and Titanium Project is an advanced project located in Minas Gerais, Brazil, roughly at latitude -19.05° South and longitude -45.934° West. The project is owned by Resouro Strategic Metals Inc. and is focused on producing upgraded titanium products from anatase-bearing feed, along with a Mixed Rare Earth Carbonate (MREC). The proposed process recovers titanium into fine and coarse product streams, while rare earth elements are captured in the MREC. At the current preliminary economic assessment stage, the product specifications and market suitability remain subject to confirmation through further testwork and product qualification.

Critical Data

Overview

The Tiros processing flowsheet takes advantage of the deposit's shallow, soft, and highly weathered mineralization. Because the material is friable, conventional crushing and milling equipment used for hard rock is not needed. The design instead relies on disaggregation and size classification to prepare the feed for the downstream beneficiation stages.

Run of mine material arrives by truck and enters a Scrubber Inlet Screen for a first separation. It then moves to a trommel scrubber, which is a rotating cylindrical drum with an internal washing and disaggregation section followed by a perforated screening section at the discharge end. High-pressure process water disperses clays and detaches fine TiO₂ and REE particles from coarser fragments. Material that meets the size requirement passes through the perforations as slurry, while oversized lumps continue to the end of the drum and go to tailings.

The disaggregated slurry is pumped to a screen with a cut size of 300 µm. This produces two streams. Material over 300 µm goes to a Rod Mill to reduce particle size and liberate target minerals. The mill discharge has a perforated screening section that separates material smaller than 300 µm. That undersize is recirculated to the screen for subsequent processing, and oversized lumps go to tailings disposal.

Material under 300 µm continues to a screen with a cut size of 75 µm. The fraction between 75 µm and 300 µm goes to the coarse circuit and becomes the titanium product stream. Material below 75 µm is routed to the REE recovery circuit, which handles the fine titanium and rare earth elements processing stream.

Key Process Stages

Coarse Circuit Titanium Dioxide Route. The coarse circuit uses an HCl-based approach to selectively remove impurities from the titanium-bearing minerals. The feed material in the 75 µm to 300 µm range enters a Low Intensity Magnetic Separation unit operating at 1,000 Gauss. This stage reduces iron content from 42.3% to 17.4% in the non-magnetic fraction. The magnetic fraction goes to a thickener and filter, with the wet solid sent to tailings.

The non-magnetic fraction proceeds to gravimetric separation, where particles are separated by specific gravity. This lowers silicon content from 16.0% to 4.5% SiO₂ in the heavy fraction. The light fraction, rich in kaolinite and quartz, goes to a thickener and filter. The heavy fraction with high anatase content goes through solid-liquid separation before entering a rotary kiln.

The rotary kiln operates at 600°C with a residence time of 60 minutes under a controlled atmosphere. Carbon monoxide, generated externally from charcoal combustion, is introduced as a gas stream to reduce iron from Fe³⁺ to Fe²⁺. This increases the magnetic susceptibility of the iron-bearing phases. The discharge from the kiln cools through an air-cooling unit to about 100°C, then a water-cooling stage brings it down to around 50°C.

The cooled material enters a second LIMS operating at approximately 2,000 Gauss. This removes residual iron-bearing minerals and reduces iron content to about 5% Fe in the non-magnetic product. The magnetic fraction goes to tailings.

Electrostatic separation follows to further reduce silica. The feed must be dry because moisture affects electrical conductivity and separator performance. Anatase reports to the conductor fraction, and silica-bearing minerals go to the non-conductor fraction and then tailings. This stage reduces SiO₂ to less than 1.0% in the conductor material.

The conductive fraction undergoes hydrochloric acid leaching at 90 to 100°C for about 90 minutes. The leach solution contains approximately 16 wt% HCl. Consumption is about 0.056 tonnes of active HCl per tonne of ROM, equivalent to 0.164 tonnes of 34% HCl solution per tonne of ROM. The anatase-rich product reaches an anticipated TiO₂ grade exceeding 80% and is proposed as the final coarse titanium product.

Fines Circuit Fine Titanium Dioxide and MREC Route. Material passing 75 µm enters the REE recovery circuit. It first goes through a LIMS operating at 800 Gauss to remove metallic minerals, particularly iron-bearing phases. The magnetic fraction goes to a thickener and filter for tailings disposal.

The non-magnetic fraction enters a rotary kiln for drying and preheating. The kiln discharge at approximately 600°C cools through an air-cooling unit to about 100°C, then a water-cooling unit brings it to around 50°C. This cooled material goes through a dry magnetic separator, with the magnetic fraction sent to tailings.

Acid baking follows in a rotary kiln using concentrated sulfuric acid. The material mixes with H₂SO₄ to form a reactive paste and undergoes thermal treatment at 300°C for about one hour. This decomposes the mineral structure and converts REE to soluble sulfates. Iron, aluminum, and titanium also react, increasing acid consumption.

An acid-regeneration unit is assumed in the process design to reduce net acid consumption. The unit operates at approximately 600°C and produces an SO₃-bearing gas that gets captured and hydrated to regenerate concentrated H₂SO₄ for recycling. This is a conceptual and untested assumption at the PEA stage and requires validation in the next study phase.

The calcine from the baking stage cools through air and water coolers before going to agitated leaching reactors. Sequential washing with water dissolves the converted REE sulfates along with iron, aluminum, and titanium sulfates. Non-converted minerals, primarily SiO₂, remain undissolved and are removed by solid-liquid separation. The clarified liquor moves on, and the low-moisture solid residue goes to tailings.

Purification and REE Carbonation. Titanium removal from the clarified sulfate liquor uses controlled neutralization with 10 wt% NaOH in agitated reactors. This promotes hydrolysis and precipitation of hydrated titanium oxide. The titanium-bearing solids are recovered by filtration. The source notes this step has not been demonstrated for the Tiros process liquor, and sodium-rare earth double sulfates may precipitate and cause REE losses to the titanium-bearing solids.

Impurity removal uses controlled addition of Mg(OH)₂ in agitated reactors. The first reactor increases pH to promote precipitation of iron and aluminum. Subsequent additions adjust pH to favor precipitation of potassium, calcium, and other ions while keeping the rare earth elements in solution. Filtration produces a clarified liquor and a low-moisture filter cake for tailings.

The purified REE liquor goes to precipitation reactors where a sodium carbonate solution is added under controlled pH and temperature. This precipitates a Mixed Rare Earth Carbonate. The slurry goes through a filter, and the solid MREC transfers to a reslurry tank for washing to reduce residual impurities. A filter press dewaters the washed slurry, producing the MREC product.

Additional Interesting Data and Summary

The process design criteria are preliminary and based on a nominal capacity of 500,000 t/a. The average feed grades are 26.27% TiO₂ and 10,852 ppm TREO, though Table 17.2 lists 26.3% TiO₂. The mass balance comes from laboratory testwork by Resouro plus preliminary design assumptions and benchmarks from analogous operations.

Global recoveries of 68.7% for TiO₂ and 67.0% for TREO are adopted for producing the fine and coarse titanium products and an MREC. At the stated throughput and feed grade, the feed contains roughly 5,426 t/a TREO, with about 3,636 t/a estimated to report to the MREC. The MREC production rate, composition, and TREO grade remain subject to confirmation.

Water requirements total approximately 391 m³/h. The breakdown by area is 130 m³/h for the coarse area, 54.5 m³/h for the fine area, 154 m³/h for reagents, 1.89 m³/h for cooling water makeup, and 50.7 m³/h for others. Water comes from local catchments and supplies process water, demineralized water, and cooling water makeup. Demineralized water is used for reagent preparation and acid dilution to minimize dissolved contaminants.

A water treatment plant is considered to process liquid streams from the solid-liquid separation stages. These streams contain dissolved solids and must be treated before reuse. The design and development of the Water Recovery System will happen in the next PFS phase.

Air supply covers instrument and equipment needs through compressors, dryers, and filters distributed to plant areas. Cooling air uses forced-air equipment sized for projected thermal loads. Diesel is stored for backup electricity generation. LPG is stored and distributed for kiln equipment. A portion of freshwater from the local river goes to a fire system tank for emergency response.

Key Processes

• Scrubbing and size classification for feed preparation
• Rod mill for coarse material size reduction and mineral liberation
• Low intensity magnetic separation at various gauss levels for iron removal
• Gravimetric separation for silica reduction
• Rotary kiln calcination and reductive roasting at 600°C
• Electrostatic separation for silica removal
• Hydrochloric acid leaching for anatase purification
• Sulfuric acid baking at 300°C for REE conversion
• Water leaching of calcine to dissolve REE sulfates
• Selective neutralization for titanium, iron, and aluminum removal
• Sodium carbonate precipitation to produce MREC

Source: NI 43-101 Technical Report and Preliminary Economic Assessment for the Tiros Rare Earths and Titanium Project, July 28, 2026. Project website: Tiros Rare Earths and Titanium Project