Emerging Graphene Technology Company
Hydrothermal Graphite Deposit Ammenable for Commercial Graphene Applications
Message: Flake chasing high purity spherical graphite is very difficult.
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From your post RR:
GIN: I’ve been told by geologists that graphite can be easily purified using acid leaching. Is that not true?
AE: Yes. You can upgrade flake thermally and with acid. It’s a little more expensive. When somebody says that they can do that I would simply ask, “what is the cost?” We know from our processing that we can do it with a caustic bake fairly cheaply.
AE: Yes. You can upgrade flake thermally and with acid. It’s a little more expensive. When somebody says that they can do that I would simply ask, “what is the cost?” We know from our processing that we can do it with a caustic bake fairly cheaply.
There certainly is a higher financial cost to purify flake graphite to these ultra high purities both from high processing costs as well as about 60-70% of the feed is lost during the process.
From NGC:
Almost all natural spherical graphite is currently produced in China and purified using strong acids which results in large volumes of acidic and toxic waste. Thermal purification at temperatures as high as 2,400 C can be used but it is expensive in terms of capital and operating costs. The proprietary purification technology developed by Northern and its metallurgical research partners is much more environmentally friendly than the Chinese approach and operates at significantly lower temperatures than traditional thermal methods. It also involves relatively low retention times in the furnace and will likely be a continuous rather than a batch process. As a result, costs should be significantly lower.
Again from NGC:
Northern has achieved spherical graphite yields of up to 70 per cent on rounding when starting with its large flake. Almost all non-synthetic spherical graphite is made from small minus-100 mesh flake in China, and yields are only about 30 per cent. Different size fractions were produced for testing and they were purified both by Northern's proprietary process and by a commercial industry process.
So only when NGC starts with large flake size do they get a 70% yield, said another way, they only lose 30% of their feed when they start with large flake size. My next question would be, how much of their deposit is large flake size? What happens to the rest of the graphite?
Another key consideration is the quality of this finished spherical graphite. Here is a quote from a research paper:
Further examamination of the flakes led to the discovery of flakes with clearly damaged edge structures, as shown in Figure 4-7 and Figure 4-8. The edges of these flakes are curled back towards the centre of the flake and the edge is severely roughened. Initially, these flakes were sonicated in a water bath for 5 min while being contained in a test tube with ethanol. This was to ensure separation of the agglomerates. Clearly, the flakes are highly malleable and damage easily.
The whole article is available here: http://upetd.up.ac.za/thesis/available/etd-04172012-190006/unrestricted/03chapter4.pdf
So while the NGC info and this research paper are not linked, there is enough supporting evidence to make a reasonable assumption that purifying flake graphite to ultra high purity is both costly and results in a lower quality end product.
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