I have been asked many times on what is the highest ash content in natural graphite that allows to purify it thermally via ETFB purification technology. So, today I am going to make another brief insight into ETFB applied for battery grade graphite > 99.95%.
First of all, why does it matter?
Commercial grades of flake graphite range between 94-97% and 45-850 µm in size. The lowest quality is related to smaller particles and worse purity. All mines are capable to supply much lower grades after floatation, because, in this case, they have higher yield. But only few of them can offer product of excellent grades > 97% at low processing costs. So the issue of second-stage purification methods and their initial conditions are sensitive for manufacturers and suppliers as well.
The technical side of the issue
Any processing technology requires feedstock of certain quality and ETFB furnaces are not an exclusion. Low-grade material may cause slag deposits on the inner lining, electrodes and waste-gas flue that, sooner or later, makes the unit inoperative. Another possible side-effect is that, at temperatures 2800-3200°C, inner graphite parts of the furnace become highly reactive and vulnerable to chemicals, because carbon is a powerful reducing agent. So, the high ash content in natural graphite and its chemical composition can dramatically affect the ETFB furnace.
What about the practice
As of now, there is no consensus about acceptable graphite grade, because processing engineers and developers familiar with the subject have a different point of view. In our labs we have investigated many carbon materials, simulating the process and conducting various stress-tests of the whole technology. So, from my experience, I can confidently say it is possible to process natural graphite of 5%, 8% and even 12% ash content. There is a set of available engineering solutions related to the furnace’s design and operating modes that ensures stabilized electric, thermal and fluidization performance. However, I have to admit, there is one setback that cannot be passed over too. Higher ash content negatively influences the furnace productivity and energy efficiency. But that is rather the subject of another discussion.
Hope this brief was useful.
All the best and have a nice day wherever you are.
February 14, 2019
by Serhii Fedorov / Thermal & Material Engineering Center – Graphite Purification Technologies
Link to follow the article: https://www.linkedin.com/pulse/what-limits-graphite-grade-before-advanced-thermal-bed-serhii-fedorov/