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 heap leach processes can be used to extract lithium and boron at high recovery rates into a Pregnant Leach Solution (“PLS”).
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.
This metallurgical testwork was conducted by Kappes Cassiday & Associates (Reno) and Hazen Research (Denver) laboratories.
Heap 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, filtration and 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 heap leach has been demonstrated to be an effective processing route.
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.
A heap leach operation at Rhyolite Ridge would likely involve the following:
- Run-of-mine ore is crushed to between 50mm and 150mm
- The crushed ore is placed on a lined pad
- The ore is irrigated with sulphuric acid/water solution via drip feeder pipes
- The metals are dissolved into solution, forming a pregnant leach solution (“PLS”)
- The PLS is collected in a pond or tank
- Boron and lithium are recovered from the PLS and converted into boric acid and lithium carbonate by a combination of crystallisation and purification process steps
The infographic below provides an overview of the proposed mining and processing steps.