Maracás Menchen Project — 2021 Technical Report

This section describes the vanadium recovery methods at the Maracás plant, including historical operating data, current process design, and planned expansions.

Report context

The Maracás vanadium recovery plant was commissioned in 2014 and achieved its nameplate capacity in 2018. An expansion project implemented in 2019 increased process capacity to 1,900,000 t/year of ROM and V₂O₅ production capacity to 12,000 t/year. In 2020, the plant produced 11,825 t of V₂O₅ with 81.5% overall recovery. Improvements in the roasting/burning system in 2021 increased production capacity to 13,200 t/year V₂O₅. At the time of writing, the plant produces up to 1,087 t of V₂O₅ equivalent per month with a trend approaching design capacity of 13,200 per year.

Processing route

Crushing and dry magnetic separation

Ore is processed through a three-stage crushing circuit comprising a primary jaw crusher, two cone crushers, and two vibrating sizing screens. The fine crushed product is fed to dry magnetic separation. Vanadium is contained within the magnetite fraction of the resource and is recovered using low intensity magnetic separators (LIMS) of 1,500 Gauss. Two roll magnetic separators, each with 150 t/h capacity, operate in parallel. The pre-magnetic concentrate is blended with the massive ore and sent to the grinding circuit.

Milling

The dry magnetic separation product is fed to a stockpile that supplies the grinding circuit, with the objective of feeding the mill at a magnetic grade of 42%. The milling stage uses two ball mills in series, each 13×26 ft with 2,275 KWh (3,000 HP). The primary mill operates in closed circuit with a hydrocyclone battery containing six hydrocyclones Krebs GMax 20 (three operating, three standby). The secondary mill operates in an indirect closed circuit with a secondary hydrocyclone battery of ten hydrocyclones Krebs GMax 20 (six operating, four standby). Primary mill uses maximum ball size of 80 mm with consumption of 250 g/t; secondary mill uses maximum ball size of 60 mm with consumption of 200 g/t. The product P80 is 106 µm.

Wet magnetic separation and concentrate filtering

Milled material is fed to low intensity magnetic separation consisting of one rougher and two cleaner stages, using four wet magnetic separators. The final magnetic concentrate is filtered using a 20 m² filter. Filtered concentrate is stockpiled to feed the roasting section. The non-magnetic concentrate fraction is thickened and pumped to the non-magnetic tailings pond.

Ilmenite flotation and filtering

Following planned expansion, the non-magnetic concentrate from the milling plant will be pumped to desliming hydrocyclones to separate slimes from coarse particles. Coarse particles will be sent to a flotation circuit with six rougher cells, one cleaner cell, and one recleaner cell, producing an ilmenite concentrate and tailings. The ilmenite concentrate will be filtered using a horizontal filter to 10% moisture and stockpiled.

Roasting

The filtered magnetic concentrate, containing approximately 3% V₂O₅, is roasted at high temperature above 1,100 °C in a rotary kiln with diameter 4.2 m and length 90 m at 1 rpm rotation. Kiln capacity is 88 t/h. Sodium carbonate (Na₂CO₃) is added at 65 kg/t of concentrate. Magnetite (Fe₃O₄) is oxidised to hematite (Fe₂O₃) after 3 hours, losing magnetic characteristics. Vanadium is extracted from magnetite structure as sodium vanadate. Fuel consumption (HFO + diesel) is 34 kg/t of concentrate. An off-gas control system with 13 t/h capacity and an electrostatic precipitator remove particulates to meet environmental regulations. The calcined material is cooled to 400 °C in a rotary cooler with diameter 4 m and length 34 m at 2 rpm.

Leaching

Calcined material is ground in a ball mill to liberate sodium vanadate. Ground material is leached for one hour and twenty minutes in each of two agitated tanks of 120 m³ capacity installed in series. The leach discharge is sent to a thickener with 14 m diameter, then filtered and washed using a vacuum belt filter. The solution containing approximately 110 g/L V₂O₅ is pumped to the chemical plant for desilication. The filter cake has 10% moisture, 60% Fe, 2.9% SiO₂, and 6.8% TiO₂ and is stockpiled.

Desilication uses 398 kg/t H₂SO₄ to reduce pH from 11 to 8 in three agitated tanks, with 111 kg/t of aluminium sulphate and sulphuric acid. After desilication, the solution is pumped to a filter where solids are removed. The filtrate, called pregnant leach solution (PLS), is pumped to precipitation.

Precipitation, evaporation, and drying

The dirty preg solution is pumped at 17 m³/h to a heat exchanger to reduce temperature below 40 °C. Vanadium is precipitated as ammonium meta-vanadate (AMV) in agitated tanks (75 m³) with addition of ammonium sulphate after 6 hours residence. The precipitate is filtered, washed, and dried prior to calcining.

A crystallisation circuit recovers sodium sulphate salt, ammonium sulphate solution, and water from barren leach liquor. The liquor is concentrated by evaporation to a predetermined ammonium sulphate concentration. At approximately 250 g/L Na₂SO₄, salt precipitates. The pulp (20% solids) is pumped to a cyclone feeding a centrifuge, producing salt sulphate solid with 5% moisture. Overflow (ammonium sulphate) is returned to precipitation.

Wet AMV (15% solids) is dried in a flash dryer with 6 t/h air capacity.

Ammonia removal and melting

Dried AMV is calcined under oxidising conditions at 600 °C in an electric kiln (Drytech, 1.5 t/h capacity). The reaction produces V₂O₅ powder. This powder can be sent to melting at 900 °C to produce fused flakes, or to screening to produce powder. Flakes are crushed and stored in silos, packed in 1-tonne bags or 250 kg drums.

V₂O₃ reactor

After start-up of the V₂O₃ plant, wet AMV from precipitation will be divided into two flows: one to the current flash dryer and one to the new V₂O₃ reaction plant comprising a flash dryer and a rotary kiln. The kiln has capacity of 942 kg AMV per hour, operating at reduced conditions at 800 °C. V₂O₃ powder is packed in 1-tonne bags or 200 kg drums.

Titanium pigment processes (proposed)

Largo intends to implement a TiO₂ pigment sulphate process in Camaçari industrial complex using ilmenite concentrate from the Maracás plant. The process includes ore storage, drying and milling, digestion with sulphuric acid to transform metal oxides to sulphates, black liquor filtration, FeSO₄ crystallisation (producing copperas for fertiliser), hydrolysis with seeding and temperature control, calcination at 900-1,000 °C to produce TiO₂ rutile, surface treatment with inorganic coatings, and micronisation using high-pressure steam. An acid regeneration plant will concentrate waste acid for recycling.

Key reported parameters

Technical qualifications

This information is derived from the section titled “17 Recovery Methods” in the Independent NI 43-101 Technical Report, Maracás Menchen Project, Bahia Brazil, titled “An Updated LOMP for Campbell Pit and Pre-Feasibility Study for GAN and NAN Deposits,” dated December 16, 2021. The process description, key design criteria, and operating data presented are as reported in that technical report. The report distinguishes between historical operating data (2020 production), current plant design parameters, and proposed testwork or planned expansions. No information on project economics, ownership, or current operational status beyond the report date is included. The V₂O₃ reactor, ilmenite plant, TiO₂ pigment plant, and future expansions at GAN and NAN deposits are described as planned or anticipated developments as of the report date.