Graphite is a crystalline form of carbon. It occurs naturally as flake, vein and amorphous graphite. These commercial forms vary in purity, crystal size and crystal shape.
Amorphous Graphite is very fine flake graphite. It has a soft black earthy appearance with crystal sizes of less than 40µm and a high ash content. Amorphous graphite is formed by the metamorphism of anthracite coal seams that may be hosted by quartzites, physllites, metagreywackes and metaconglomerates. It is primarily used for lubricant products. It is the least graphitic with the lowest carbon purity of the three graphite forms.
Vein Graphite (also known as Lump Graphite) occurs naturally in fissures or fractures. It forms as platy intergrowths of fibrous or needle-like crystals. It is believed to be of hydrothermal origin (heated by hot water moving through fissures in the earth) naturally occurring in gneiss, schist, quartzite and marble. Vein graphite is predominantly used in thermal and high-friction appliances, for example car brakes and clutches.
Flake Graphite is the least common form of graphite and the most expensive. Prices can be up to 4x higher than for amorphous graphite. Flake graphite has a very high purity of +85% carbon. Flake graphite is found in schists or gneisses derived from the metamorphism of carbonaceous sedimentary rocks ranging from Archean to Mesoproterozoic age. It occurs as discrete, platy crystals. High quality crystal flake graphite is required in the production of emerging technologies but is currently in limited supply.
Flake Graphite Concentrate from Hexagon Resources’ Emperor Deposit
GRAPHITE AND GRAPHENE
Graphite has a hexagonal crystal structure, is black to grey in colour and is opaque, lustrous, soft (hardness 1-2 Mohs) and greasy to the touch. It is a non-metallic mineral which is light, strong, non-corrosive, conductive and heat resistant. Its low frictional resistance makes it an excellent lubricant. Graphite resists attack from most acids and has extremely good refractory properties. The properties of graphite depend entirely on the purity and size of the graphite crystal.
Graphene is a layer of carbon atoms in a single layer bonded together in a hexagonal lattice. It is the thinnest compound known to man at one atom thick, the lightest, the strongest (200 times stronger than steel), the best conductor of heat at room temperature and the best conductor of electricity. Graphene was first isolated into individual sheets in 2004. It has the potential to make aircraft 70% lighter and charge batteries 10 times faster and store 10 times more power. The potential of graphene has earned it the title of ‘The world’s next wonder material’ by the American Chemical Society. Current research is targeting the ability to produce graphene on thin pieces of metal (tens of nanometers thick), using chemical vapours at low temperatures. Once this is achieved graphene will be more widely available for commercial uses.
PROCESSING FLAKE GRAPHITE
Processing graphite is a two-step process. First the flake graphite is milled and concentrated by liberation from the host rock. This involves using roller mills and cone crushers to liberate the graphite into difference size fractions. This process finely grinds granular contaminants (for example, quartz and feldspar) allowing the flake graphite to slip through relatively unaffected. Further separation is achieved through flotation which adds reagents to coat the graphite flakes and caustic soda to adjust the pH which improves selectivity.
The second beneficiation step examines the concentrate to see if the correct liberation size has been achieved and if the graphite has been completely freed from the host rock. If this is not the case, re-grinding to the next largest sieve size is necessary. The process of regrinding and microscopic examination is repeated until the optimum liberation size is achieved.
China is currently the leading graphite producer, producing 780,000 tonnes in 2014. India has increased production by over 1000% from just 15,000 tonnes in 2011 to 170,000 tonnes in 2014 to be the second highest graphite producer. Brazil produced 80,000 tonnes in 2014 and Canada, North Korea and Turkey produced 30,000 tonnes.
Total world production has been increasing annually, with an increase of almost 150% since 2000 taking production from 480,000 tonnes to 1,116,000 tonnes in 2014.
Major producers of graphite in 2014. SOURCE: USGS Mineral commodity Summaries 2014
There is no open market for graphite so prices are negotiated directly between the producer and customer. Graphite price is a function of flake size and purity. Large flake (180+µm or 80+ mesh) and high carbon (+94%) varieties achieve premium pricing.
New high-growth applications such as lithium-ion batteries and fuel cells have not yet had a substantial impact on demand and consumption. These applications are expected to make a significant impact on graphite prices over the longer term.
Graphite is primarily used for refractories, batteries, steelmaking, lubricants and automotive parts. The purity and flake size of graphite affects its end use.
Green energy applications such as lithium-ion batteries, fuel cells and nuclear power will increase demand for graphite in the future.
Lithium-ion batteries have a very high energy density which enables them to store large amounts of electricity. The battery anodes require 10-20 times more flake graphite than lithium carbonate. The average hybrid electric car uses more than 10kg of graphite in its battery and a fully electric car uses up to 70kg.
High end technological applications such as lithium-ion batteries require large flake, high purity (high carbon content) graphite. This is why flake graphite commands a premium pricing.
Fuel cells are energy conversion devices that convert fuel such as hydrogen into electrical energy. Within the fuel cell, the proton exchange membrane requires large quantities of graphite. Fuel cells of all sizes are currently emerging in the electronics and utility sectors where they can provide emergency power.
The increasing demand for graphite is highlighted by the company Tesla (an American automotive and energy storage company), who are currently building a Gigafactory in Nevada. Tesla is expected to begin cell production in 2017 and reach full capacity in 2020. Their planned production rate for electric cars is 500,000 per year. The Gigafactory will produce more lithium ion batteries annually than were produced worldwide in 2013. For more information see the Tesla website
Schematic for Tesla’s Gigafactory in Nevada from teslamotors.com
In the linked video, Dr. Ian Flint speaks of misconceptions about graphite and Teslas’s challenge to find enough graphite for its Gigafactory in the USA.
Pebble-bed nuclear energy generators are small, modular reactors that are becoming important in the energy sector. Pebble bed reactors use uranium fuel embedded in a golf ball-sized graphite-coated pebbles that act as moderators. These pebbles are supplied in a controlled flow to the reactor core where thousands of pebbles are amassed for the generation of heat. Spent fuel pebbles are tapped off at the base of the rector. A 100GW pebble-bed reactor requires 300 tonnes of graphite for start-up, and a further 60 – 100 tonnes per annum of graphite for continual operation (Pistilli, 2012).
Schematic of Pebble Bed Reactor
Fetherston, JM 2015. Graphite in Western Australia: Geological Survey of Western Australia, Mineral Resources Bulletin 26, 84p.
Pistilli, M 2012. Types of graphite: amorphous, flake and vein: Investing News, viewed 18 February 2014, <http;//graphiteinvestingnews.com/1337-types-graphite-amorphous-flake-lump-vein-energizer-focus-northern-syrah-northern>.