SYR SP Discussion, page-273

Perhaps impurities in the ore have a greater impact than the figures suggest.

Blackrock has proved that it can achieve 99.1% TGC by flotation alone. Reducing requirements for chemical processing is both financially and environmentally rewarding.

I have also read that some impurities such as sulphur, vanadium, molybdenum etc in graphite ore can be less attractive to different battery technologies as it can react unfavourably with chemicals used in those batteries.

So buyers might press for a lower price due to the chemical composition of the impurities (or use it as an excuse if it matters not).

Note that I am invested in blackrock so my views are biased.