Graphite is a mineral that owing to its unique structure and conductivity is widely used in a variety of industries. There are impurities found in the natural graphite ore composition which varies from one graphite mine to another. Graphite purification is the process of purifying the natural graphite of its impurity components to source the usable purified graphite.
Graphite is a form of crystalline carbon that occurs naturally and is found in igneous and metamorphic rocks. The value of graphite depends on it carbon content and flake size. As a mineral graphite is extremely resistant to heat and nearly inert when it comes into contact with almost all other materials. It has a very low specific gravity and is extremely soft. It is thanks to these varying qualities that graphite is popular in a range of manufacturing industries.
When carbon is subjected to pressure and heat along Earth’s crust it forms the mineral graphite, which is why it is most often found as crystalline layers or flakes in metamorphic rocks. It is sometimes found in coal beds and organic rich shales.
A graphite source is considered as high purity when it has more than 99.9% graphite content. The composition of each graphite ore is unique when it comes to impurity components, though the impurities are generally similar. Graphite purification rids natural graphite of these impurities.
Fastmarkets has forecast that the consumption of natural graphite in the ion battery sector to rise on par with the consumption in the refractories sector this year. It is predicted that the consumption will exceed refectories in 2024. Basically the high demand in the industries of carbon fibre, reinforced plastics, conductors and graphite electrodes amongst a host of others, continues to drive the market growth.
For natural graphite to be used it needs to undergo purification to remove impurities which vary from batch to batch. Before purification, it is important to first find out the content of impurities in the graphite ore composition. The composition changes according to the location of the mine. Pure graphite material has many purposes such as the core of nuclear reactors, batteries, lubricants, pencils, crucibles, foundry facings, polishes and brushes for electric motors to name a few.
When natural graphite is mined its carbon content is generally low except in the case of vein graphite. To be used graphite has to undergo a purification process. The purification process helps remove impurities and enrich the graphite to create the refined product needed for many industries. High purity graphite mines require less purification processes to achieve the required carbon ratio. Common impurities found in graphite mainly include potassium, sodium, aluminium, calcium, magnesium and other silicate minerals. Natural flake graphite is purified to improve the carbon content to about 99.68–99.72%.
There are a few purification methods used which include the use of hydrofluoric acid, alkali acid, flotation, chlorination roasting and high temperature – which is the method of physical purification. The other methods are categorised as chemical purification methods. High temperature or thermal purification is done at temperatures over 2500 °C and does produce a higher purity graphite. However this process involves the need for expensive temperature furnaces to be built and operated, has a high energy consumption and adds to environmental pollution.
The initial purification process includes the process of crushing which releases the graphite flakes from the mineral parent rock. This helps improve the beneficiation efficiency. The size of the flakes and the carbon content of the sourced graphite are the most important factors in determining the final grade of the graphite. The method of crushing is decided based on the type of graphite ore. Next comes the grinding and screening to ensure maximum recovery of the graphite flakes which leads to the final stage which is the actual purification process using the methods mentioned above.
Chemical purification further removes hydrophobic impurities with acid washing being one of the most commonly used methods. It creates a chemical reaction between the varies acids used and impurity substances. It not only purifies graphite but also acts as a pre-treatment before the flotation process. Chemical purification can help obtain graphite with a purity level of about 99.5% and has a relatively low cost compared to other methods. Further it has less impact on the environment and waste liquid can be filtered easily.
Purified graphite is the wonder material of many modern industries which is why the demand for graphite is ever increasing.
Pencils- Starting with its simple yet very important role as the lead for pencils. Being resistant to moisture, most chemicals, ultraviolet with natural ageing qualities, the mark left by graphite on paper can actually be removed or erased with rubber. Graphite is a safe alternative to the actual lead used previously.
Batteries – This is where the demand for graphite is ever increasing as the modern world pulses around the portable source of energy provided by batteries. Graphite serves as a lithium ion host for negative electrodes and protects batteries when overheated. It is the preferred and most cost effective material for ion batteries thanks to its high conductivity and why it is used in fast charging batteries. These batteries are commonly used in phones, electric cars, in emergency power backups or UPS and solar power storage to name a few.
Bio medical and sports industries – Graphite plays a pivotal role in the bio medical, bio sensing and membrane technology. It is also used in the production of sports material to the outer layers as it adds a layer of ultra-strength, agility and durability.
Electrical industry – Graphite in its crystalline form is used in the electrical industry because it has a high electric conductivity and the ability to transfer heat away from critical components.
Steel industry – Graphite powder is used as a carbon raiser which gives steel is immense strength and is used as a protective agent for steel ingots, while graphite electrodes and connecting pins are used in electric arc furnace steel production.
Nuclear reactors/refractories – Thanks to its ability to withstand intense high temperatures and pressure in its pure form, graphite plays an important role in nuclear reactors. Again, due to its high thermal resistance and mechanical stability to such high temperatures it is used as a counter-electrode in furnaces for refractories.
Playing such a pivotal role in numerous industries it is no wonder that pure graphite is in such high demand, which is why graphite purification has an integral part to play in providing this pure graphite for industry use.