Overview
The Rhyolite Ridge Lithium-Boron Project, located in Esmeralda County, Nevada, stands as one of the most significant strategic mineral developments in North America. Owned and operated by Ioneer Ltd, this project represents a unique geological occurrence: a large-scale, shallow sedimentary deposit containing both lithium and boron. Unlike typical lithium-bearing pegmatites or continental brines, Rhyolite Ridge is characterized by the presence of searlesite—a sodium borosilicate mineral—interbedded with lithium-rich smectite and illite clays. This mineralogical combination allows for a co-product revenue stream that significantly offsets the cost of lithium production, positioning the facility at the bottom of the global lithium cost curve.
Situated approximately 65 kilometers west of Tonopah, the project is nestled within the Basin and Range province of the United States. Its strategic importance cannot be overstated, as it provides a critical domestic source of lithium carbonate for the burgeoning electric vehicle (EV) battery supply chain and boric acid for a wide array of industrial applications, including glass, ceramics, and agriculture. The project is designed to be a high-output, long-life operation, with a mine life exceeding 26 years. By utilizing an innovative on-site processing circuit that integrates sulfuric acid vat leaching with advanced crystallization and purification stages, Rhyolite Ridge is set to become a cornerstone of the “Green Energy” revolution in the Western Hemisphere. The facility’s development involves rigorous environmental oversight, particularly regarding the protection of the endemic Tiehm’s buckwheat, ensuring that industrial advancement is balanced with ecological stewardship.
Key Process Stages
The processing circuit at Rhyolite Ridge is a sophisticated multi-stage facility designed to handle approximately 2.5 million tonnes of ore per year. The circuit is engineered to maximize the recovery of both lithium and boron through a series of chemical and mechanical separation steps. The primary stages of the processing circuit are outlined below:
- Ore Preparation and Blending: Run-of-mine (ROM) ore is delivered to a crushing circuit where it is reduced to a specific particle size distribution (P80) optimized for leaching. Blending is critical here to ensure a consistent feed grade of both lithium and boron, which stabilizes downstream chemical consumption.
- Vat Leaching: The crushed ore is loaded into large vats where it is subjected to a dilute sulfuric acid leach at controlled temperatures (approximately 60°C). This stage is highly efficient for searlesite-rich ore, as it dissolves the lithium and boron into a Pregnant Leach Solution (PLS) while leaving much of the gangue material as a solid residue.
- Primary Impurity Removal: The PLS contains various impurities such as iron, aluminum, and magnesium. Through a series of pH adjustments and precipitation stages, these elements are removed to prevent interference with the crystallization of final products.
- Boric Acid Crystallization: The purified PLS is cooled to approximately 15°C. Because boric acid has a temperature-dependent solubility, this cooling process causes boric acid to crystallize out of the solution. The crystals are then filtered, washed, and dried for sale.
- Secondary Purification and Magnesium Removal: Following boron recovery, the solution undergoes further purification using ion exchange (IX) or chemical precipitation to remove remaining divalent cations (calcium and magnesium), ensuring the lithium stream is of the highest possible purity.
- Lithium Carbonate Precipitation: The concentrated lithium solution is reacted with sodium carbonate (soda ash). This triggers the precipitation of lithium carbonate. For battery-grade specifications, a bicarbonate purification stage is often employed to re-dissolve and re-precipitate the lithium, further eliminating trace contaminants.
- Zero Liquid Discharge (ZLD) and Tailings Management: The remaining barren solution is processed through an evaporator/crystallizer circuit to recover water and produce sulfate-based byproducts. The solid leach residue is washed, filtered, and moved to a dry-stack tailings storage facility (TSF).
Critical Data
The following table summarizes the projected technical and operational parameters for the Rhyolite Ridge processing facility based on technical feasibility studies.
| Parameter | Value | Unit |
|---|---|---|
| Annual Ore Throughput | 2,500,000 | Tonnes per Annum (tpa) |
| Lithium Carbonate Production | 22,000 | Tonnes per Annum (tpa) |
| Boric Acid Production | 174,000 | Tonnes per Annum (tpa) |
| Lithium Recovery Rate | 85.0 | % |
| Boron Recovery Rate | 88.0 | % |
| Acid Plant Capacity (Sulfuric Acid) | 3,500 | Tonnes per Day (tpd) |
| On-site Power Generation (Cogeneration) | 35 | Megawatts (MW) |
| Mine Life | 26+ | Years |
Technical Details and Sustainability
The technical sophistication of the Rhyolite Ridge project extends beyond its primary recovery circuits into its utility and environmental management systems. A defining feature of the site is the integration of a 3,500 tonne-per-day sulfuric acid plant. The production of sulfuric acid is an exothermic process, generating a significant amount of waste heat. Ioneer utilizes this heat through a state-of-the-art cogeneration plant to produce approximately 35 MW of carbon-free electricity. This power is sufficient to run the entire processing facility and mine, making the project virtually self-sufficient regarding energy and significantly reducing its carbon footprint compared to mines that rely on grid-tie power or diesel generators.
Furthermore, the choice of vat leaching over traditional stirred-tank leaching offers several technical advantages. Vat leaching typically requires less energy for agitation and allows for the processing of coarser material, which simplifies the solid-liquid separation stages. In the context of the Rhyolite Ridge searlesite ore, vat leaching achieves high extraction rates (up to 95% for boron) while minimizing the dissolution of silicate minerals that would otherwise complicate the downstream purification of lithium. The use of a “closed-loop” water system is another critical technical detail. By utilizing mechanical vapor recompression (MVR) and multi-effect evaporators, the facility recovers up to 75% of the water used in the process, which is then recycled back to the leach vats. This is particularly vital given the project’s location in the arid environment of Nevada.
From a sustainability perspective, the project has pioneered new methods for tailings management. Rather than traditional wet tailings ponds, which pose risks of leakage and require vast amounts of water, Rhyolite Ridge utilizes dry-stack tailings. The neutralized leach residue is filtered to a low moisture content and compacted in a stable, lined facility. This method improves geotechnical stability and facilitates concurrent reclamation. Environmental protection also extends to the local flora. The project has undergone extensive redesigns to avoid the habitat of Tiehm’s buckwheat (Eriogonum tiehmii), including the establishment of a buffer zone and the funding of botanical research to ensure the plant’s long-term viability. This proactive approach to ESG (Environmental, Social, and Governance) factors is essential for securing the social license to operate in the modern mining landscape.
As the global demand for high-purity lithium carbonate continues to surge, the Rhyolite Ridge project’s ability to produce two high-value products from a single domestic source provides a massive competitive advantage. The integration of chemical processing with renewable energy generation and advanced water recycling serves as a blueprint for the future of sustainable mineral extraction. By bridging the gap between traditional mining and advanced chemical manufacturing, Ioneer is positioning Rhyolite Ridge as a critical node in the global transition to a low-carbon economy.
Source: Rhyolite
Source: NI 43-101 Technical Report
This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.
