The importance of cenospheres can be summed up in a not-so-recent quote by an anonymous chemical trader from India, who wrote on the Go4worldbusiness trading platform, “We require Cenospheres immediately.”
It is unknown whether the request was successful or not, for the post had no positive feedback listed. Instead, the request was met with a further 8 postings of chemical traders also hoping to buy. Clearly there is a demand for cenospheres, but what is less clear is exactly what they are.
With this in mind, here is a brief outline of the what, the where, the when, and perhaps most importantly, the how much of cenospheres.
What are Cenospheres?
Named from the Greek words kenos (hollow) and sphaera (sphere), cenospheres are balls of aluminium silicate, a material similar to glass, that are filled with a mix of oxygen, nitrogen and carbon dioxide. They measure between 10 and 600 micrometers, and so appear dust like to the human eye.
They can be extracted from underground deposits laid down 65 million years ago (when the meteor that killed the dinosaurs impacted Earth), or more commonly, they are taken from the fly ash that is created as a by-product from coal-fired power stations. As a result, many power plants adjust their combustion parameters so as to obtain desired quantities and qualities of recoverable cenospheres.
Although they are a product of a fossil fuel resource, they are often seen as a more ecologically friendly chemical feedstock, as they find a use for a waste product. Even though cenospheres constitute only 1%-3% of fly ash, this waste would normally be buried, or taken away on the wind where it pollutes the air.
Tackling even a small part of the waste from power stations is environmentally helpful, as the amount of waste created by power generation is huge. According to National Geographic, “Fly ash and the other residuals of burned coal add up to one of the largest waste streams in the United States: More than 136 million tons per year. In Europe, coal waste totals 100 million tons per year by some estimates. Similar figures aren’t available for China, but since it is now burning more coal than the United States, the waste generation is significant. Scientists at the China Building Materials Academy and the Institute of Technical Information for Building Materials Industry calculate that their country has accumulated 2.5 billion tons of coal ash.”
How Much are Cenospheres Worth?
This is a very difficult question to answer, as due to cenospheres relative low weight and high volume they are often used as fillers for more expensive plastics, construction materials and composites. So the value of cenospheres is largely set by the value of the raw material they are replacing.
However, Karen Wood in the industry journal Composites World notes that, “The cost of microspheres varies considerably depending on a variety of factors, including material, density, strength and volume. Expancel microspheres, for example, range in price from $5/lb to $30/lb [$12/kg to $70/kg], depending on grade and volume. The manufacturing process employed in the production of the microsphere also affects cost.” While plastics consultant Paul A. Tres, former president of ETS Inc. points out that, “In general, high-strength, glass microspheres cost two to three times more than chopped glass fiber.”
However, the French industry journal, Industrie & Technologies, states that, “[While the price of cenospheres is] difficult to assess, the market is certainly growing. One good indicator, [is that] the price of a ton has doubled in the past two years.”
Where are Cenospheres From?
In general, where ever there is fly ash, there are cenospheres, which means that the world’s largest producers are based in China, Russia, the U.S. and India. Although, there is plenty of fly ash to go around, with the journal, Industrie & Technologies estimating that, “[The] More than 50,000 [coal-fired power] plants worldwide produce more than 1 billion tons of fly ash every year.”
The journal continues to explain how, “The main method of recovering cenospheres is a wet method, as due to their low density and hollow nature, cenospheres float. They are then collected on the surface of settling ponds, either by suction or mechanically, and then dried. Triboelectric [separation by use of electrical charge] or centrifugal systems are also in use, depending on the quantities to be treated, [which] then allows them to be separated from heavier particles containing carbon and iron.”
A cenosphere settling pool in the Netherlands, courtesy of cenosphere supplier PMS.
What are the Technical Specifications of Cenospheres?
As a rough guide, the ceramic particles in fly ash have three types of structure. The first type are hollow and are called cenospheres. The second are solid and called precipitator, while the third type of particles are called plerospheres [from the Greek pleres meaning filled], and are hollow particles with a larger diameter that contain smaller precipitators and cenospheres.
They vary in colour, from white to dark grey, depending on the raw material used, their size, the burning process used, their wall thickness, and the materials that they are made from. So, to quote Industrie & Technologies, “The smaller cenospheres have a higher content of silica (SiO2) and aluminum oxide (Al2O3) with a perfectly empty internal structure, while the larger ones have a lower SiO2 and Al2O3 content, but a more resilient inner structure.” Their chemical make-up also gives them their alternative name of alumosilicate microspheres.
The journal continues by outlining that, “The thickness of the wall also varies greatly according to their size, [which is] between 2.5% and 10.5% of the diameter of the cenosphere. Also, their magnetic properties may vary according to their composition. The structure of the cenospheres defines their density (apparent 0.3-0.5g/cm3, actual 0.6-0.7g/cm3), their thermal conductivity (0.1-0.2 W/mK), their mechanical strength (210-350kg /cm2), their thermal stability (sintering between 1000-1450°C), and their resistance to acids. They are also chemically inert.”
Who Trades Cenospheres?
What is key, is that the specifications of cenospheres differ greatly from place to place and plant to plant, and this can make for a number of niche markets which smart chemical traders are able to exploit.
Buyers must therefore spend time either nurturing relationships between existing suppliers, or by doing the leg work in finding a new cenosphere supplier whose product meets the necessary standards.
Recommended contacts include the Expancel wing of AkzoNobel, which is one of the world’s largest suppliers of cenospheres, and Alibaba of course, who seems to sell everything. Cenosphere buyers who prefer a more trustworthy source are also advised to contact AG Chemi group (who pay for this blog), as all traders working through them are certified as genuine.
Overall, the cenosphere market can be described as expanding, with the number of applications available to these small balls of alumosilicate microspheres growing. New markets have been established among battery manufacturers, plastics producers, in paints and industrial coatings, as well as in the construction industry. While developers of modern composites are finding new uses all the time, including in the automobile industry as a lightweight alternative to aluminium.
You can read more about the growing number of applications for cenospheres in part two of this blog here.