Graphite resources around the world have been the focus of
intensive exploration over the past seven years to help meet
projected growth in demand for the carbon mineral from
fast-expanding technologies such as lithium-ion batteries.
Projects under development range from greenfield sites in
northern Canada to mothballed mines in South Australia,
presenting a variety of ore types that require customized
processing methods to produce the most lucrative high-grade
The claims of environmental friendliness made by several of
the end-markets that are driving the rise in battery-grade
graphite consumption, such as electric vehicles and renewable
energy storage, have attracted increased scrutiny on the supply
chains of raw materials.
This has put graphite companies under pressure to
demonstrate environmental sensitivity in the way they add value
Currently, graphite ore is mostly beneficiated using
flotation separation techniques, followed by acid leaching and
According to Dr Saeed Chehreh Chelgani, adjunct professor at
the University of Michigan in the United States, who has
studied the effectiveness and environmental impact of
different graphite processing methods, refining graphite
through roasting and leaching is both costly and potentially
polluting due to energy inefficiency and the production of
"There are different projects looking at ways to reduce the
environmental problems of leaching and caustic roasting,"
Chelgani told Industrial Minerals.
"Microwave pre-treatment, as well as liquid-liquid flotation
and bioleaching, are some examples of studies which have had
successful results. But these trials are continuing, to meet
the specific needs of industry," he said.
|SEMs are used to analyses the effectiveness of
graphite beneficiation methods.
Penn State, via Flickr
Benefits of microwave irradiation
Microwave irradiation has many advantages over roasting. It
allows for rapid and selective heating, fast switch-on and
-off, flexible modular design of treatment units and high
It is also relatively benign in environmental terms.
Microwave pre-treatment makes the graphite more receptive to
subsequent chemical treatment, meaning that smaller amounts of
chemicals can be used to increase the mineral’s
The capacity of microwaves to selectively heat graphite ore
means that this technique is especially effective in targeting
"The organic component of graphite is a relatively weak
absorber of microwave energy, whereas some minerals, such as
pyrite, and water in their structures, readily heat within an
applied electric field. Other minerals, such as quartz, appear
transparent to the radiation," Chelgani explained.
"By applying various microwave energies, pyrite may be
selectively heated and decomposed as pyrrhotite or iron
sulfate," he added. "Furthermore, in response to the effects
of microwave irradiation, the bonds of sulfur-carbon in
organic sulfur compounds contained in the graphite ore are
broken and the sulfur is released in gaseous form."
Leaching experiments with hydrochloric acid (Cl) and nitric
acid (HNO3) and microwave radiation showed increases in the
grade of the graphite tested to 99.43% C from 95%.
Scanning electron microscope (SEM) and X-ray power
diffraction (XRD) analysis of the resulting products
indicated that the shape of the graphite flakes remained
unchanged during this process. This is especially important
for applications such as batteries, where large flake
material is currently essential.
Microwave treatment of graphite dates back at least to
around 1984, with many studies also performed on coal, but the
technology has so far not been widely adopted in place of
"Microwave irradiation was not considered a promising method
of upgrading natural graphite until quite recently. I have not
heard of its industrial application in graphite processing
yet," Chelgani said.
Chelgani is skeptical about claims from graphite producers
that there is a looming shortage of large flake graphite,
arguing that recycling and using artificial graphite can
cover part of the anticipated future demand.
"For sure, natural graphite is performs better [than
synthetic graphite] because it has been structured over a
million years under geological conditions which created some
specific properties in its structure," he said.
But ultimately, as Chelgani pointed out, commercial graphite
users choose their raw material according to a cost-performance
balance. Until new processing techniques can be shown to
contribute positively to industry margins, incumbent methods
will be difficult to dislodge.
MLA: Liberate to accumulate
Since size and grade are among the most important
determinants of graphite’s sale value, high-grade
ores with a large fraction of naturally occurring large flakes
need to be processed in ways that do not crush these prized
Liberating these flakes within the ore is key to maximizing
their recovery, studies have found.
Mineral liberation analysis (MLA) by automated SEM-based
image analysis can be used to determine which beneficiation
techniques are the most effective in liberating large
MLA can also be used to gather useful data on impurities,
grain size distribution and composition of mineral
association of any given graphite sample, which cannot be
obtained by other analytical tools that are currently
But MLA is a relatively expensive technique and the machines
needed to perform the analysis are scarce, meaning that
graphite samples must usually be shipped hundreds or even
thousands of miles to research laboratories to be
While increasing use of MLA technology could potentially
boost adoption of new methods of graphite processing, this
will depend on commercial factors such as cost, perceived
shortages of supply and the selling price of graphite