The proposed Rhyolite Ridge processing flowsheet uses well-proven conventional processing technology and the mineralisation does not require roasting to liberate the lithium and boron.
Metallurgical testwork has demonstrated that simple, low-cost vat or heap leach processing can be used to extract lithium and boron at high recovery rates into a Pregnant Leach Solution (“PLS”). Vat leaching has been selected as the preferred processing technology for Rhyolite Ridge.
Lithium and boron can then be removed from the PLS through crystallisation and purification steps to produce lithium carbonate and boric acid at the mine.
The acid leaching metallurgical testwork has been conducted by Kappes Cassiday & Associates (Reno) and Hazen Research (Denver) laboratories.
Vat leach extraction of lithium and boron at modest acid consumption rates means significantly lower capital and operating costs are likely when compared to other forms of acid leaching such as agitation (tank) leaching that require crushing, grinding, flotation and agitation leach tanks. It also means substantially lower capital and operating costs when compared to hard-rock lithium deposits (spodumene, mica, clay) that require beneficiation and high temperature conversion or roasting to liberate the lithium prior to the lithium carbonate production process.
The Company believes Rhyolite Ridge is the first lithium project where both vat and heap leach have been demonstrated to be effective processing routes.
The key results from the vat leach testwork are:
- Coarse feed: crushed to minus 25mm
- Rapid leach times: < 7 days to achieve recoveries to PLS of >90% for lithium and boron
- Moderate net acid consumption: circa 400 kg per tonne of ore
- Provides the most concentrated PLS with consistent composition, thus simplifying downstream processing
The key results from the heap leach testwork were:
- Coarse feed: crushed to minus 38mm
- Rapid leach times: 15 days to achieve recoveries to PLS: 97% for lithium and 98% for boron
- Moderate net acid consumption: 413kg per tonne of ore
- High permeability and high percolation rates maintained throughout tests
- Excellent column integrity: low mass loss (21%) and low slumping (<5%)
- No agglomeration required
An overview of the heap leach flowsheet for Rhyolite Ridge is provided in the diagram below.
The infographic below provides an overview of the proposed mining and processing steps.