Tests find MRL graphite
suitable for lithium batteries
MRL Corporation (ASX: MRF) has received a significant boost in its strategy to become a lucrative graphite producer, with key metallurgical test work showing its graphite exceeds the grades required for use in lithium ion battery anodes.
Testing conducted at the Wuhan University of Technology (WUT) found graphite from MRL’s Aluketiya project in Sri Lanka contained 99.98% Total Graphitic Carbon (TGC).
Further test work will be conducted to refine the process flow sheet and provide more detail on the suitability of MRL’s graphite for premium-end product use.
Tests using an acid leaching process returned 99.66% TGC and those using acid roasting returned 99.96% TGC. Testing is ongoing with a view to simplifying the metallurgical flow sheet and achieving grade of at least 99.95% TGC though acid leaching techniques.
MRL believes the results were particularly pleasing because the graphite used was the lowest-grade unprocessed bulk sample material, which had an initial grade of 93.1% TGC.
The expected average grade of vein graphite to be mined by MRL is more than 95% TGC.
Typical high-grade Sri Lankan graphite achieves a greater recovery rate than most disseminated flake graphite deposits due to its reduced physical processing requirement and much higher starting TGC purity.
About MRL Corporation Ltd (ASX: MRF)
MRL is aiming to develop an underground mining operation to extract high-grade, crystalline vein graphite, which is unique to Sri Lanka. The Company holds exclusive rights to exploration licenses covering approximately 6,300 hectares in area, with historical workings located within nearly all license grids.
About Graphite
Natural graphite occurs in three forms: amorphous graphite, flake graphite and the most rare and highest quality form being crystalline vein graphite. Sri Lanka is famed for being the only commercial producer of crystalline vein graphite (lump or Ceylon graphite), the highest quality of naturally occurring material in the world.
The quality of vein graphite produced in the country has a purity level in excess of 90% TGC (Carbon as graphite) which means little upgrading and processing is required to make a high quality saleable product.
Amorphous (micro crystalline) graphite is the least pure form of naturally occurring graphite and commercial deposits usually have a carbon content of 70-85%, and are found as lenses or lumps with flat fracture cleavages.
It is normally formed by metamorphism of previously existing anthracite coal seams.
Flake (crystalline) graphite is the more common form of graphite and typically has carbon content in the range of 80-99%, and is usually formed in metamorphic rock in concentrations of 5%-12% of the ore body. Mining and processing of these deposits is similar to open pit gold or copper mines, requiring ‘large scale’ mining and processing to extract the graphite. Large-scale mining and processing plants typically equates to high capital expenditures and relatively high operating costs.
Vein (crystalline) graphite is the purest form of graphite with TGC grades typically >90%, with some grade as high as 99.5% TGC.
Mining vein graphite may be considered analogous to high-grade gold vein mining, requiring considerably less capital expenditure when compared to large-scale open pit mining. That is, development, mining equipment and processing plants will be of a significantly smaller scale. Operating unit costs will also be lower than those for typical large-scale open pit mining.
Nature of vein graphite
Sri Lankan graphite deposition model is best described from the ‘bottom up’: tension fractures formed in the metamorphic sediments, caused by the folding of the sediments, creating ‘conduits’ for the hydrothermal deposition of high quality vein graphite.
Historically, mining of these veins has found the veins generally increase in thickness and grade quality with increasing depth. Graphite veins generally dip steeply at –70° to near vertical, enabling ‘narrow vein’ extraction mining techniques similar to those used on narrow vein, high-grade gold deposits. The method commonly used is an overhead retreat stopping technique where the high-grade vein graphite is mined and hauled to surface without contamination.
The graphite selvages, in contact with the surrounding waste, is hauled to surface and stockpiled for upgrading. The balance of the waste is used to fill the floor of the stope.
Due to the nature of the vein graphite, it is anticipated vein widths of ~25cm, using narrow vein mining techniques can be economically extracted from underground operations.
