Processing Facilities
Processing
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 utilise 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.
Take a virtual tour of the Rhyolite Ridge Lithium-Boron Project plant – Engineering Model Rendering (Narrated by Bernard Rowe during 2022 AGM):
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.
Testing and Pilot Plant
The Company’s pilot plant established all process input / output parameters for the process facility, including but not limited to phase chemistry, throughputs, recovery results, reagent consumption, process equipment forecast efficiencies.
- Invested over $10 million in metallurgical test work and piloting
- Conducted two- five- and seven- meter lithium-boron ore column leaching tests at Kappes, Cassiday & Associates in Reno, Nevada
- Operated pilot plant over 2 years at Kemetco Research
- Simulation of process flowsheet in a continuous cycle processed over 30 tonnes of Rhyolite Ridge ore
- Developed data from test work required for detailed design and engineering of process plant with integrated support from Fluor, Veolia, FLSmidth, RMS, Woodgrove, and Kemetco Research
- Production of high-quality boric acid, lithium hydroxide and lithium carbonate to support off-take and marketing activities