The overall site plan for the Rhyolite Ridge Project is shown below. The compact project site extends from the mine quarry in the west to the processing facilities and spent ore storage facility (SOSF) in the east. The processing facilities are approximately 1.8 miles northwest of the quarry and 1 mile north of the spent ore storage facility.
Overall Site Plan
The mining operations will consist of a conventional drill-and-blast, load-and-haul operation. Ore will be trucked from the mine quarry to the nearby ore processing stockpile over a new heavy haul road. The ore will be reclaimed by a loader and fed to the crushing plant.
Development of the Rhyolite Ridge quarry will occur in two stages:
- Quarry Stage 1 - Starter Pit. An initial starter pit will be developed in the southwestern part of the ore body to supply ore for the first 4.5 years of the Project. In this area, lithium grades are 15% higher than the average grade for the deposit and the ore is more exposed at surface.
- Quarry Stage 2. Development of the greater pit will start once the environmental permits for this development have been granted. The Stage 2 pit design will facilitate a larger mining area to be maintained, aiding the efficiency of the operation for another 21 years. Stage 2 will involve expansion to the south and east. Finally, mining will progress to the north of the deposit. The Stage 2 pit requires prestripping to begin in year 4.
Pit Development Stage 1 (Starter Pit) and Stage 2
Owner mining is planned to be undertaken utilising a highly automated equipment fleet which will provide a lower operating and capital cost, while minimizing injury and safety related incidents. In order to optimize operations, the mining fleet will be equipped with high precision GPS and real time analytics, allowing excavator and wheel loader operators to know what type of material is being loaded.
ioneer will capitalize on current mining advances to enhance project performance including:
- Haul Truck Automation. ioneer will become the first greenfield site in the U.S to use automated haul trucks in the initial operation. This has shown to have several advantages in operating and capital costs in addition to minimizing safety incidents.
- Mining Selectivity. To minimize the effects of loss and dilution in the mining operation, an accurate geologic model, high-precision GPS, competent operators, and a fleet management system (FMS) will be used. These packages will allow excavator and wheel loader operators to know in real time what type of material is being loaded.
The Rhyolite Ridge lithium-boron ore zone is increasing in grade and shallowing to the south, meaning the delineation of additional ore to the south, outside of the current Mineral Resource, is likely and would be expected to have a significant positive impact on the mine plan and project economics. Access to the southern extension of the deposit for drilling was not possible during the previous drilling campaign due to statutory limits on surface disturbance during the exploration phase. This area is scheduled for drilling once the necessary permits are in place, expected in 2Q 2021.
ioneer’s lithium and boron products will be produced using an energy-neutral process with zero carbon dioxide (CO2) emissions from electricity generation, resulting in a process plant with low emissions of greenhouse gases and minimal hazardous air pollutants. Water usage associated with ioneer’s mineral extraction process is a fraction of that of other lithium producers that utilize a more conventional brine extraction and solar evaporation methodology
The final processing design was derived after thousands of hours of bench and pilot plant test work conducted by Fluor, Kemetco Research, Kappes Cassiday, with support from Veolia and FLSchmidt. Based on these efforts, the project’s engineering team (led by Fluor) designed the Project’s processing facilities using known and commercially proven technology to accommodate the unique Rhyolite Ridge ore. The test work produced a clear understanding of the processing chemistry, sequences, and understanding of the set points for optimal operations, and allowed ioneer to produce a complete mass balance based upon bench scale and pilot-level verification. This work was used as the basis to develop the plant’s engineering, cost estimates, and production forecasts in the Overall recoveries are estimated to be 85% for the lithium carbonate, 95% for lithium hydroxide, and 79% for the boric acid.
The Rhyolite Ridge process plant general layout is shown below and consists of the main unit operations described below:
Ore Processing Facilities and Sulphuric Acid Plant - General Layout
- Ore Sizing. Blended ore is transported by belt conveyor to the primary and secondary sizers where the coarse ore particles are crushed to less than ¾ inch. The crushed ore is conveyed and stacked directly into the leaching vats. A unique property of the Rhyolite Ridge ore is that large particles are readily leachable and do not require expensive size reduction and milling to achieve high lithium and boron extraction rates.
- Vat Leaching. The vat leaching process uses a series of 7 vats where crushed ore is sequentially leached for 3 days with diluted sulphuric acid. The vats operate in a counter-current configuration, made possible by the unique Rhyolite Ridge ore particles remaining largely intact and free-draining during the leach process. Counter-current leaching minimizes the overall leaching time and acid consumption. The spent ore undergoes a displacement wash to remove valuable interstitial lithium and boron in solution. The spent ore is free draining, allowing the vat to be emptied of solution and produces a residue material that is suitable for dry stacking. High lithium and boron recoveries in leaching are consistently achieved at low to moderate temperatures (60°C) and moderate free-acidity levels.
- Boric Acid Circuit. Crystallization of boric acid is achieved by cooling the vat leach solution (referred to as PLS – pregnant leach solution). Since the PLS is close to saturation in boric acid, the cooling effect in the crystallizer produces boric acid crystals. The boric acid crystals are separated using centrifuges and then undergo a second-stage recrystallization for purification. Most of the boric acid is recovered with minimal contamination from sulphate salts.
Evaporation and Crystallization Circuit. The main evaporation and crystallization circuit is designed to concentrate lithium and remove sulphate salts and other impurities. The solution (mother liquor) from the boric acid crystallization undergoes impurity removal of aluminum and other elements and is then pumped to a 4-stage evaporator circuit to remove 70% contained water and concentrate the lithium. Crystals of sulphate salts and boric acid are produced, the latter being recovered by flotation and recycled to the boric acid crystallization circuit. Sulphate salts are sent to the spent ore storage facility. Water vapor from the evaporators is condensed and reused throughout the process.
This evaporation and crystallization process is critical to the concentration of the lithium to a high-level suitable for the lithium carbonate circuit. This process replaces evaporation ponds required in brine operations.
Lithium carbonate circuit. The lithium carbonate circuit is designed to produce technical-grade lithium carbonate from the lithium brine mother liquor. The first step is to remove the remaining magnesium from solution by precipitation with lime slurry. Lithium carbonate is then precipitated from the magnesium free mother liquor using soda ash. The precipitated lithium carbonate is filtered, washed, and dried.
For the first 3 years, lithium carbonate will be sold as technical-grade product (99% purity). From year 4 onward, lithium carbonate will be converted into lithium hydroxide (99.5%) as described below.
Sulphuric acid plant. A 3,860 short tons per day (stpd) sulphuric acid plant will produce commercial-grade (98.5%) sulphuric acid for vat leaching the ore; steam to drive the evaporation and crystallization steps; and electricity to drive the entire process. The plant will generate 35 MW of electricity – sufficient to run the entire facility and will be separate from the Nevada state power grid.
The selection of the technology for the large sulphuric acid plant is based on a proven operating design and specialty technology provider (MECS-DuPont). The acid plant is a double conversion- double absorption system that has proven to be reliable and predictable. It includes a tail gas scrubber system that results in an ultra-low emissions plant (12 ppm SO2 and 15 ppm NOx).
Lithium hydroxide circuit (Year 3). The Rhyolite Ridge process flowsheet demonstrates a strong synergy for the installation of an onsite lithium hydroxide circuit. Installation of the circuit is planned for year 3, allowing the main plant to be operating smoothly before the addition. The conversion of Rhyolite Ridge technical-grade lithium carbonate to battery-grade lithium hydroxide by the liming method takes advantage of the following:
- Ideally suited technical-grade lithium carbonate produced in the plant
- Excess steam and power generated in the sulphuric acid plant
- Recycling of calcium carbonate formed during production of lithium hydroxide for use in the impurity removal process within the main plant, thereby reducing reagent cost and lithium losses
- Existing ancillary systems such as dryers and bagging equipment
ioneer’s design is directed toward recycling water, to the extent possible, which further reduces make-up water demands. Low-energy consumption, substantially reduced water needs, and relatively small surface footprint make Rhyolite Ridge a sustainable, environmentally sensitive operation.
The Rhyolite Ridge process is expected to produce quality products at an overall recovery of 85% for lithium carbonate, 95% for the lithium hydroxide circuit, and 79% for boric acid, excellent yields for these products, particularly lithium.