The Gibellini Vanadium Project in Eureka County, Nevada, proposes to recover vanadium pentoxide (V₂O₅) from open pit mines using an acid heap leach and solvent extraction process, a novel application of established technology.
The Gibellini Vanadium Project, located in Eureka County, Nevada, is a Preliminary Economic Assessment (PEA) focused on extracting vanadium from the Gibellini and Louie Hill open pit mines. The process plant design applies heap-leach technology and standard proven equipment to vanadium recovery, a combination not previously implemented commercially. While heap leaching and solvent extraction are common in the mining industry, notably in copper operations where acid leach solution mobilizes the metal followed by solvent extraction and electro-winning, the Gibellini process instead employs an acid strip followed by precipitation to yield a final product. The design is based on metallurgical test work and is intended to match the crush and recovery characteristics of the different oxidation states of the mineralization. The project is currently in the development stage based on the PEA status.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Heap leach stack height | 15 | ft | Agglomerated leach feed material |
| Leach solution application rate | 0.0025 | gal/min/ft² | Applied to stacked material |
| Feed size to crusher (upper) | 4 | in | Material greater than 4 in sent to stockpile |
| Feed size to crusher (lower) | 1/3 | in | Material between 1/3 in and 4 in sent to cone crusher |
| Feed size to agglomerator | Minus 1/2 | in | Crushed material fed to agglomerator |
| Strip solution strength | 225 to 250 | g/L | Sulfuric acid strip solution |
| Process water flow to raffinate tank | 300 | gal/min | Gravity feed from make-up pond |
| Water truck capacity | 10,000 | gal | Filled on average 12.5 times per day |
| Make-up water usage | 125,000 | gal/day | 10,000 gal tanker × 12.5 loads |
| Total V₂O₅ production | 210,000,000 | lb | From Gibellini leaching operations |
| Average recovery | 62 | % | Oxide: 60%, transition: 70%, reduced: 52% |
Overview
The Gibellini Vanadium Project is designed around a heap leach operation treating mineralized material from two open pit sources, the Gibellini and Louie Hill deposits. The process route uses sulfuric acid heap leaching to mobilize vanadium into solution, followed by solvent extraction to concentrate and purify the pregnant solution, and precipitation to produce ammonium metavanadate (AMV). The AMV is then dried, calcined, and melted in a multi-hearth furnace to produce the final vanadium pentoxide product. Approximately 210 million pounds of V₂O₅ will be produced at an average recovery of 62%, with oxidation state-specific recoveries of 60% for oxide material, 70% for transition material, and 52% for reduced material.
Key Process Stages
Mineralized material from the open pit mines is fed via loader to a hopper feeding the screening and crushing plant. The screen sends material greater than one-third inch and less than four inches to a cone crusher, while material over four inches is sent to stockpile for further treatment. Crushed material recycles to the screen feed belt, forming a closed crushing circuit.
The minus half-inch mineralized material is fed to the agglomerator where sulfuric acid, flocculant (agglomeration aid), and water are added to achieve proper agglomeration. The agglomerated leach feed is transported to a stacker on the leach pad, which stacks the material to a height of 15 feet. Once sufficient material is accumulated to permit sprinkler distribution, solution is added at a rate of 0.0025 gal/min/ft². The solution percolates through the heap and is collected in a pond as pregnant leach solution (PLS) and sent to the process building for metal recovery.
PLS is pumped from the collection pond to a reduction tank where milk of lime modifies the pH and sulfur dioxide solution modifies the oxidation-reduction potential (ORP). The solution passes through a plate and frame filter press to remove gypsum sludge, with clear solution sent to solvent extraction and sludge sent to the agglomerator.
The PLS is treated with iron to convert vanadium from the vanadate (VO₃⁻) form to the vanadyl (VO²⁺) form, which is preferentially loaded onto the organic phase in the extraction circuit. A set of solvent extraction mixer-settlers recovers vanadium onto the organic phase, producing a vanadium-depleted aqueous solution (raffinate) that is returned to the leach pad to continue leaching.
The loaded organic phase advances to the strip circuit, a separate set of mixer-settlers where vanadium is pulled from the organic phase into a new aqueous phase using a 225 to 250 g/L sulfuric acid strip solution. The stripped organic returns to the extraction circuit for re-loading. Periodic washing of the organic with HCl may be necessary to remove ferric iron; this could be done periodically or through a continuously processed partial sidestream.
The pregnant strip solution advances to a tank where sodium chlorate oxidizes all vanadyl ion (blue) to vanadate (yellow). Anhydrous ammonia is then added to precipitate ammonium metavanadate (AMV). The precipitate slurry overflows into a thickener where it is mixed with flocculant in the center well. Thickener underflow is sent to a centrifuge for additional dewatering before being fed to a multi-hearth furnace for drying, calcining, and melting. The melt flows from the bottom of the furnace to a casting wheel where the V₂O₅ cools to a crystalline form. As the solid is removed from the casting wheel, it is crushed and packaged in one-ton supersacks.
Thickener overflow is acidified with 225 to 250 g/L sulfuric acid and returned to the strip circuit as barren strip solution for re-loading with vanadium.
Additional Interesting Data and Summary
Process water will gravity feed from the make-up pond to the raffinate tank at a flow rate of 300 gal/min. Water will also be pumped from the make-up pond to a 10,000-gallon water truck on average 12.5 times per day, providing an additional 125,000 gallons per day of water. During construction, water will be supplied to construction trucks.
Reagents required during processing operations include sulfuric acid, polymer, kerosene, diethyl-hexa phosphoric acid (DEHPA), tri-octyl phosphorous oxide (TOPO), ammonia, sodium chlorate, sulfur dioxide and/or powdered iron, electrical power, diesel, and propane. Process water requirements have been appropriately considered in the design, with water assumed to be sourced from wells. Power for the process route is assumed to be supplied from a new distribution line to be constructed to the Project, with requirements incorporated in capital and operating cost allocations. Reagent requirements have been established for the operational throughput.
The majority of the metal production occurs within the same reporting period as material is placed on the leach pad. Following Year 5, the overall deposit grade drops.
Key Processes
- Crushing and screening of mineralized material to minus 1/2 inch
- Agglomeration with sulfuric acid, flocculant, and water
- Heap leaching with sulfuric acid solution at a rate of 0.0025 gal/min/ft²
- Solvent extraction using mixer-settlers with DEHPA/TOPO organic phase
- Stripping with 225 to 250 g/L sulfuric acid
- Oxidation with sodium chlorate and precipitation with ammonia to form AMV
- Centrifugal dewatering, drying, calcining, and melting in a multi-hearth furnace
- Casting, crushing, and packaging of V₂O₅ in one-ton supersacks
Source: Gibellini Vanadium Project , 2018 Technical Report, Section 17.0 Recovery Methods, June 2018.
Project website: Gibellini Vanadium Project, 2018 Technical Report
