Anthracite Applications in Today's World
Far from being burned as coal for heating or power generation, the modern uses of anthracite - the superior grade of coal - are numerous. African Pegmatite supplies high quality anthracite for a myriad of uses, milled to any specification, for any process use.
When looking through the type of coals available that can be used, anthracite coal is the type that is the highest quality because of its increased carbon content. Due to the fact that it has spent over 350 million years underground in the midst of intense heat and pressure, it is the purest form of coal that you can get, oftentimes in excess of 90% carbon by weight. As such, it also has the highest capacity to produce energy for an extended period of time.
There is no denying the importance and relevance of coal to this day. As one of the major sources of carbon, it is used in all types of industries ranging from power, construction, furnace, farming and more. The Industrial Revolution would never have happened without coal.
Another reason why anthracite is preferred over all other types of coal is because it is considered to be the cleanest. As far as coal goes, the burning of anthracite releases fewer toxic gases compared to other forms of coal, for example lignite.
In recognition of the vast utility that this material extends, many industries prefer its use over any others. As such, there has been a steady rise in the development of technology that allows for companies to properly harness the power of the coal so that it can be put to great use.
What are some of the uses of anthracite coal?
It can be used for a variety of purposes in all fields and industries. Some of the common uses of are as follows:
- Heating Systems
As one of the most brittle kinds of coal, anthracite is the perfect resource to use for the generation of heat for an extended amount of time. As the coal is burnt, it produces a hot blue flame that can generate enough heat to power the heating systems of entire buildings, homes and offices. Considering even the smallest amount of this material will last longer than wood, it is considered to be economical and efficient.
With a high carbon content, it is perfect for use in steel making industries. It is always ready for use in its natural form and does not need to go through the process of coking as other types of coal have to go through. Its long lasting nature makes it perfect for smelting, fabrication, furnace companies, briquetting charcoal, the production of iron ore pellets and so much more in the metal industry.
It was also called ‘Hard Coal’ because of its tough nature. It was considered to be the perfect source of fuel for trains by locomotive engineers. While not many trains are powered by coal anymore, there are still some out there that still utilise this form of coal. It is especially important to use cleaner burning coal to reduce localised pollution levels.
- Anthracite Water Filtration Systems
This material has a specific density and unique shape that is perfect for use in water filtration systems. When used with sand as a filter, anthracite water filtration is considered to be one of the most efficient ways to clean industrial, processed, pool, waste and municipal water and restore it for the purposes of drinking and using.
Most of this high grade coal, that is extracted, often has the lowest moisture, this means that when used for water filtration, it has the ability to deflect water absorption and facilitate nano-filtration. Additionally, their irregular shape ensures their efficacy as it does not pack down into the sand causing a free flow of water without any backwashing –due to the pre-filtration layer formed.
The sheer size is convenient for use in water filtration systems because they can be removed from the water system just as easily as they are put in.
Benefits of Anthracite
- Compared to sand, anthracite allows a higher flow of water
- When using anthracite, there is less pressure drop compared to sand filters
- Anthracite allows for a stronger and backwash than most filter media - meaning the filter is easier and faster to restore
Anthracite is often used as a filter alongside sand, with which it produces one of the most reliable and simple filtration pathways.
Reverse Osmosis Water Treatment For Desalination
As reverse osmosis desalination requires the use of a partially permeable membrane to be effective, there is a strong requirement to ensure that this membrane is physically not blocked. Because of the source of the water, any number of water carried debris can present at the membrane including small aquatic organisms, gravel, microplastics and plant matter.
Using anthracite as part of a pre-reverse osmosis filtration setup is common to help alleviate mechanical blockages(1). This crucial filtration phase is important as a blocked membrane cannot remove the salt from the water at all.
In RO systems, anthracite’s filtration target is the removal of dissolved or partially dissolved organic material (such as oils - anthracite is organophillic) and suspended solids(2). Additionally, anthracite provides general size exclusion filtration - partly powered by its well suited packing properties and desirable porosity - in addition to the removal of biological materials(3).
Modern RO plants equipped with dual media filters containing anthracite can treat on the order of 40 to 50 m3 of salt water per hour(4,5) producing WHO standards compliant drinking water, with the anthracite responsible for removing particle sizes in the 0.35 to 0.80 mm size range. ‘Spent’ anthracite is discarded after use.
RO systems are known for their high energy demands and poor water recovery. Anthracite equipped RO systems have been shown to achieve in excess of 35% water recovery over one year(6), which is an improvement on non-anthracite equipped systems.
It remains true to say that a desalination plant would be useless without effective filtration. Anthracite finds other applications as part of dual media filter set ups in solvent extraction systems, such as is used in electrowinning:
Anthracite Solvent Extraction
Besides water filtration systems, anthracite solvent extraction is also quite the rage these days. It is considered to be one of the most efficient ways to clean the flow of electrolytes in solvent extraction and electrowinning during the production of copper. When using dual media filters, the solvent extraction system will improve the quality of cathodes all the while minimising costs as much as possible.
Solvent extraction electrowinning is a widely used and robust technique that is used to isolate metals from their ores. As the process relies on sequential stages of solvent extraction before an electrolysis stage, filtration is important to remove undesirables and prevent them from reaching the electrolysis chamber. The latest generation solvent extraction electrowinning plants use sequential deionised beds containing anthracite and garnet dual media filter set ups. Charged with the removal of organic residues and as a general filter, anthracite’s coarse nature makes it an ideal choice at removing suspended solids, salts and other residues. Solvent extraction electrowinning is used extensively for the production of high grade copper, cobalt, zinc and nickel from their ores(7,8).
Redox Glass Carbon
By combining this with Sulphur and Iron salts, a new compound is produced that can allow for yellow or amber colored glass and darker shades. Additionally, these compounds can also improve the strength of the glass all the while removing all its venerable qualities.
The reason why anthracite is the perfect material to use for redox glass carbon is because it will reduce the prospects of molten glass formation. This is done through improving the chemistry and make of the glass and transforming it into a higher quality end product. Similarly, the addition of carbon also reduces the gaseous imperfections induced when sodium sulphate is added to the mix. The addition of anthracite has only a moderate impact on the batch redox number.
Anthracite As A Refractory Material
Perhaps counterintuitively, anthracite has certain refractory uses - despite the fact that at high temperatures it has a tendency to combust. Smelter linings are one of several uses in the modern foundry, where anthracite is used as part of the refractory lining of the bases (hearths) of blast furnaces. Refractory bricks, pastes and other vital parts of the foundry make extensive use of anthracite. Calcined and electrically calcined anthracite have yet more uses in the foundry; from electrodes to tundish linings to ramming pastes.
Anthracite In Metal Casting
Metal casting refers to the process by which molten metal is formed into a shape by being poured into a mould. Anthracite has become a vital tool in the modern foundryman’s arsenal and is responsible for critical processes such as preventing wetting and burn on:
Greensand castings: preventing burn on using anthracite
Surface defects are the scourge of the metal casting world and is a broad term for a variety of surface defects. In one instance, they refer to a process whereby the molten metal adheres to the sand and therefore penetration of the sand by the metal occurs - these metal burrs must be machined off the final product by hand. Historically, any source of carbon would do in an effort to prevent this. Bituminous coal would have been used as this combusts in situ and prevents penetration - but also emits hazardous pollutants such as toluene, benzene and xylene. Replacement of this with anthracite dramatically reduces hazardous gas release(9,10) with no detriment to performance.
A further type of surface defect is ‘burn on’ - which is where iron oxide is produced and deposited at the surface due to the reaction between the molten iron and the volatile organics given off by burning bituminous coal(11). Replacing the bituminous coal with anthracite reduces the volatile organic production, therefore preventing oxide formation.
Wetting in castables: prevention using anthracite
Properly, wetting can be considered as a cause of surface defect formation. Wetting creates surface defects and has traditionally been alleviated by using coal dust or anthracite throughout the sand (not necessarily greensand). Research suggests that wetting is prevented by the pyrolysis (not combustion) of carbonaceous material at high temperatures, whereupon a thin film of solid carbon is deposited at the sand metal interface(12). The formation of this layer is thought to prevent any penetration and therefore the formation of surface defects. Ideal coal candidates for this include anthracite, owing to its good coking capacity, low volatile content, low ash and low sulfur content.
A small pressure increase is to be expected due to the pyrolysis process. This is normal and moderate - it is easily tolerated by the sand and metal. Any hydrogen produced, however, can penetrate the metal as it has a small enough atomic radius(13).
In metals recycling, often compound mixtures of years before refined metals are combined in an arc furnace so they can be re-cast. Naturally, separation of mixed metals is crucial and typically a reducing agent such as charcoal or coke is used to effect zinc separation from iron. Research has shown that milled anthracite can be used for this process, with the ability to reduce and thus remove zinc oxides in efficiencies exceeding 80%(14).
- Black Oxide
African Pegmatite’s carbon based black oxide is used to incorporate pigment into ceramic glazes, polishing compounds, filler, construction material and even inks. Due to the fact that this organic natural black oxide is one of the best sources of pure carbon and supports high temperatures for a longer period of time, it is the perfect material for the process of black oxide. The carbon based black oxide layering will provide a strong and stable layer of coloring and that resists corrosion as well.
- Uses in battery and supercapacitor technology
As the world progresses away from fossil fuel usage for its power generation and transportation needs, new methods of electricity storage are required. Anthracite has long been used as an electrode material in various electrochemical cells for the purpose of metal treatment, but contemporary research shows potential promising use cases as electrodes in novel batteries. Such batteries revolve around alkali metal chemistries, with one example being where pyrolysed anthracite was used in a relatively standard sodium battery cell affording 267.7 mA h g−1 of reversible capacity, 5 A g-1 of long term cycling ability and in excess of 85% of storage retention after 2,000 cycles(15). Another example using a low temperature pyrolysed anthracite electrode employed it in a lithium/potassium ion cell, where storage capacities reached 384.5 mA h g−1 and excellent storage retention(16). The authors noted that anthracite was especially well suited as an anode for batteries owing to its abundance of micropores and surface defects being especially good performing active sites for metal cation (Li+/Na+/K+) storage. Anthracite could be a highly useful choice for electrode material - it is abundant and relatively inexpensive. At the scales required, using materials like graphite for the electrode will become prohibitively expensive.
In addition to being used as an electrode in its own right, anthracite has been shown to be an ideal source for the production of a synthetic graphite analogue used as an anode in batteries. Negating graphite’s ubiquity issue, residual iron oxide content in anthracite was found to regulate the production of ‘onion-like’ layers akin to naturally occurring graphite(17).
Anthracite is able to improve upon already successful anode/battery systems. Research has shown that the addition of anthracite to a red phosphorus anode increases its specific capacity to 810 mA h g−1 from 420 mA h g−1 for the pure phosphorus(18). Using anthracite in this way has benefits not only in performance increases, but also in lowering costs and increasing robustness.
As anthracite has already been established as a good conductor of electricity, it follows that research should proceed into whether or not it is a good supercapacitor. Anthracite based active carbon (ABAC) supercapacitors have been prepared and exhibited 288.52 and 260.30 F g-1 of capacitance (i.e. storage) in acidic and basic electrolyte solutions respectively. Especially encouraging is the ABAC’s excellent capacitance retention of 95.4% after 1,000 cycles(19).
Overall when considering applications in batteries, density is a critical factor. Batteries need to have lower weight densities. Typical battery densities are often in the region of 2.6 to 2.9 g cm3, whereas employing anthracite as either filler or anode can bring mass densities down to 1.3 to 1.8 g cm3(20). Combined with previous examples of high energy density (capacitance/storage), the choice of anthracite is a promising one.
- Anthracite is the highest quality coal available - prized for its high carbon content, it is the preferred choice if using coal as a fuel
- It has many uses beyond combustion however, including in water filtration, solvent extraction, as a refractory material and in metal casting
- Because of anthracite’s high carbon content, it burns cleaner than other types of coal (c.f. lignite) and therefore emits less toxic compounds upon combustion
- Contemporary uses for fine anthracite include as anodes for batteries and in supercapacitors
Anthracite is the superior choice of coal and is the ideal material as a carbon source, with applications from the foundry all the way to the desalination plant. African Pegmatite is a leading supplier and miller of the finest quality anthracite for every application.
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