The by product is extremely fine and has only been around for a few years....purity is very low ~88% to 90% as the feed stock is normally 95% purity and during the spheroidisation process much of the gang material is released into the fines produced.
Depending on the signature source, the ash content could have high levels of SiO2 and Fe2O3 making the product very abrasive and susceptible to oxidation. Very limited on uses because difficult to purify due to the low purity...I have seen one product (D90 5 Micron) priced at US$ 1,000 MT EXW and used in some thread compounds and low grade open gear grease products. But with standard natural flake graphite either mesh sized or micronized, the quality and purity are much higher without the higher levels of SiO2 and Fe2O3, better QAQC...prices are much higher though.
Most SPG waste is PSD classified and bagged for sale with no post processing.
Because of the newness of the product, very limited information on SPG waste product. Most information comes from direct contact with customers that have used or sampled the product.
