In a recent news release, ZEN said this:  A preliminary assessment of results, including several diagnostic leach tests, indicates that achieving a purity of 99.9% Cg may be impractical and that ZHL is the most promising of the three alternatives. The process operates at 50 degrees C, will require relatively simple equipment and also has a low reagent and energy consumption. While the caustic bake/leach process yields a marginally better purity, its use as a second stage purification would suffer from the same deficiencies identified in previous work including a loss of approximately 11% of the feed graphite, difficulty in recycling leach solutions along with high energy and reagent consumption."  http://www.zenyatta.ca/article/press-release-4539.asp

In athe Investorintel story, they said this: "The Zenyatta graphite deposit can be upgraded without the use of aggressive acids and high temperature thermal treatment. Zenyatta has discovered an easy and environmentally friendly process that consist of grinding, floating and caustic treatment using sodium hydroxide. The Company has been able to achieve an ‘extraordinary’ carbon purity result of  >99.9 percent in bench-scale tests, using this proprietary and environmentally safe method of purification."  https://investorintel.com/sectors/technology-metals/technology-metals-intel/zenyatta-ventures-is-developing-a-unique-graphite-resource-to-serve-growing-global-needs/

In the latest article on mining.com, they said this:  "With the help of tech companies and researchers, the plan is to upgrade hydrothermal graphite with very good crystallinity using an environmentally friendly process that consists of grinding, floating and caustic treatment using sodium hydroxide instead of aggressive acids. This purification method has produced a carbon purity of >99.9 per cent in bench-scale tests."   http://www.mining.com/canadian-miner-first-nation-work-together-new-wonder-material-project/

They have said the most likely method they'll use for purification is the ZHL process, which involves hydrofluoric acid. But they tout the caustic method in their promotional articles, going as far as stating they won't use aggressive acids. Surely that's going to come back to bite them in the butt.