This feasibility study report details the proposed processing route for the Elk Creek Project, covering comminution, hydrometallurgical separation, and pyrometallurgical conversion to produce ferroniobium.
Report context
This NI 43-101 technical report presents the feasibility study for the Elk Creek Project, dated 2019. The report describes proposed process plant design criteria for three main processing areas: surface crushing, ore storage and mineral processing; hydrometallurgical processing; and pyrometallurgical processing. The design criteria are supported by bench and pilot scale test work conducted by SGS, Hazen, and KPM, as well as thermodynamic calculations and standard industry practices.
Processing route
Surface crushing and mineral processing
The comminution circuit is designed for dry processing of ore to avoid an expensive drying operation prior to acid leaching. The process design receives a primary crusher product with a characteristic particle size (P80) of 115 mm at the comminution circuit feed bin and produces feed material for downstream hydrometallurgical processing at a P80 of 1.1 mm.
The primary crusher product is fed to a secondary cone crusher system, operating in closed circuit with a double deck screen. The screen undersize from the cone crusher system is fed to an HPGR unit, operating in closed circuit with another double deck screen. The HPGR screen undersize becomes the comminution product that reports to the hydrometallurgical process.
The HPGR circuit consists of a single HPGR crusher with a separate double-deck vibrating screen with top and bottom deck aperture sizes of 6 mm and 3 mm, respectively. The recirculating load of the HPGR circuit is expected to be in the range of 30 to 40% of the circuit new feed. The HPGR screen undersize has a design P80 of 1.1 mm and is stored in a fine ore bin with 48 hours storage time and 6,000 tonnes live capacity, then reclaimed by vibrating feeders for the acid leach circuit.
Hydrometallurgical plant
The hydrometallurgical plant is designed to extract pay metals (niobium, titanium, and scandium) while separating them from impurities through a series of successive leach and purification steps. The process design criteria were established based on bench and pilot scale test work by SGS, Hazen, and KPM, as well as similar projects and standard industry practices.
The plant consists of 15 unit processes: Hydrochloric Acid Leach (605), Sulphuric Acid Bake (610), Water Leach (615), Iron Reduction (620), Niobium Precipitation and Phosphorus Removal (625), Scandium Precipitation (628), Sulphate Calcining and Mixed Oxides Handling (630), Titanium Precipitation (635), Scandium Solvent Extraction (640), Scandium Refining (645), Product Handling and Packaging (650), Sulphuric Acid Plant (655), Hydrochloric Acid Regeneration (660), Tailings Neutralization (665), and Tailings Filtration (670).
The Hydrochloric Acid Leach unit leaches the majority of impurities and scandium from the feed material. Feed at 2,764 t/d (115 t/h) is fed to two parallel trains, each with one primary and two secondary HCl leach tanks. Discharge slurries at 9 wt% solids are dewatered through a thickener and four parallel filter presses with counter-current washing. The filter cake proceeds to the Acid Bake unit, while filtrate and wash liquor are sent to PLS Aging ahead of scandium solvent extraction and HCl regeneration.
The Sulphuric Acid Bake unit converts unleached metal content into sulphate compounds. HCl leach cake is combined with pre-heated sulphuric acid, mixed in pug mills, and fed to a hollow flight screw maintained at reaction temperature of 300°C. The Water Leach unit solubilizes soluble sulphates through three cascading agitated tanks discharging to centrifuges. The Iron Reduction unit reduces Fe2(SO4)3 to FeSO4 and TiOSO4 to Ti2O(SO4)2 using iron solids at room temperature.
Niobium Precipitation uses water dilution to selectively hydrolyze niobium sulphate and precipitate it as niobium oxyhydroxide at 90-100°C with 4 hours residence time. The precipitate is calcined at 950°C to convert to Nb2O5, then leached with 35 wt% sodium hydroxide at 105°C for phosphorus removal. Titanium Precipitation is achieved through hydrolysis at 100°C with 2 hours residence time, followed by calcination at 950°C to produce TiO2.
Scandium recovery uses a four-stage D2EHPA solvent extraction circuit with wash, scrubbing, and stripping stages. Scandium is precipitated as oxalate and calcined to Sc2O3 at 1050°C.
The acid regeneration circuits recover 99% of HCl and 85% of H2SO4. The sulphuric acid plant regenerates SO2 from calciner off-gas, with a design conversion rate of 99.7% producing 96 wt% H2SO4. The plant can operate at 50% of design capacity and has a minimum SO2 concentration of 5 vol% for autothermal operation.
Pyrometallurgical plant
The pyrometallurgical plant reduces niobium pentoxide to ferroniobium metal using aluminothermic reduction. The process design criteria were established based on thermodynamic calculations inspired by KPM test results and supported by literature on aluminothermic reduction and niobium pyrometallurgy.
The dry Nb2O5 precipitate pellets (2.94 t/h dry basis, 64.7 t/d, with 30.5% Nb2O5 and 63.5% TiO2) are fed with aluminum shots (0.52 t/h) and hematite Fe2O3 pellets (0.48 t/h) as iron units, plus fluxes (limestone and sodium oxide), into a single electrical arc furnace operating at 1900°C. The furnace has a design power of 1,000 kW with 60% thermal efficiency. The exothermic chemical reduction produces FeNb metal alloy with a designed composition of 63.3% Nb, 33.2% Fe, 0.9% Ti, 0.3% P, and 1.4% Al. Niobium recovery to metal is 96%.
The FeNb metal is tapped 4 times per day (2 taps per 12-hour shift) at 5.5 tonnes per tap. The molten metal is pelletized in a cold-water basin to form particles of approximately 6-15 mm, dried, and screened. Slag is tapped 36 times per day at 3.94 tonnes per tap, crushed, and processed by gravity separation to recover FeNb particles before disposal.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Comminution feed P80 | 115 | mm | Design |
| HPGR product P80 | 1.1 | mm | Design |
| HPGR fresh feed throughput | 139 | t/h | Design |
| HPGR specific energy consumption | 4.18 | kWh/t | Design |
| HPGR screen top deck opening | 6 | mm | Design |
| HPGR screen bottom deck opening | 3 | mm | Design |
| Fine ore bin live capacity | 6,000 | t | Design |
| Fine ore bin storage time | 48 | h | Design |
| Hydromet feed rate | 2,764 | dmt/d | Design |
| Hydromet feed Nb2O5 grade | 0.81 | %w/w | Mine plan |
| Hydromet feed Sc2O3 grade | 100.75 | ppm | Mine plan |
| HCl leach residence time | 3.3 | h | Test work |
| HCl leach temperature | 40 | °C | Test work |
| Acid bake temperature | 220 (pug mill) / 300 (hollow flight) | °C | Test work |
| Acid addition rate (acid bake) | 925 | kg/mt | Design |
| Nb precipitation temperature | 90-100 | °C | Test work |
| Nb precipitation residence time | 4 | h | Test work |
| Nb calcination temperature | 950 | °C | Test work |
| Nb caustic leach temperature | 105 | °C | Test work |
| Nb caustic solution strength | 35 | wt% | Test work |
| Ti precipitation temperature | 100 | °C | Test work |
| Ti precipitation residence time | 2 | h | Test work |
| Ti calcination temperature | 950 | °C | Test work |
| Sc solvent extraction O:A ratio | 1:8 | – | Mass balance |
| Sc calcination temperature | 1050 | °C | Test work |
| HCl recovery | 99 | % | Design |
| H2SO4 recovery | 85 | % | Design |
| Pyromet Nb2O5 precipitate feed | 2.94 | t/h | Design |
| Pyromet Nb2O5 precipitate grade | 30.5 | %w/w | Design |
| Furnace operating temperature | 1900 | °C | Design |
| Furnace design power | 1,000 | kW | Design |
| Furnace thermal efficiency | 60 | % | Design |
| Nb recovery to metal | 96 | % | Design |
| FeNb alloy Nb grade | 63.3 | %w/w | Design |
| FeNb alloy Fe grade | 33.2 | %w/w | Design |
| FeNb production rate | 19.4 | t/d | Design |
| Slag production rate | 61.6 | t/d | Design |
| Acid plant SO2 conversion | 99.7 | % | Design |
| Acid plant product concentration | 96 | wt% H2SO4 | Design |
| Acid plant annual production | 1,038,425 | t/a | Design |
| Mineral processing installed power | 4,000 | kVA | Design |
| Hydromet installed power | 25,546 | kVA | Design |
| Pyromet installed power | 5,200 | kVA | Design |
Project website: https://www.niocorp.com/elk-creek-project/
Technical qualifications
The report notes that the majority of the unit processes selected for the hydrometallurgical flowsheet have been extensively reported on in literature and are predominately proven and existing processes. The pyrometallurgical process design criteria were established based on thermodynamic calculations inspired by test results and supported by literature. The FeNb furnace partition coefficients were estimated based on KPM test work, slag and alloy chemistry, and data from other FeNb alloy industry operations. The power requirement for the pyrometallurgical plant was estimated based on scoping test work and calculations from previous FeNb test work (XPS, KPM, and Hazen), with furnace equipment vendors confirming the estimated power requirement.
Source: NI 43-101 Technical Report Feasibility Study – Elk Creek Project, NioCorp Developments Ltd., 2019, Section 17: Recovery Methods
