FYI
Reply from supplier:
Thanks for your enquiry re Bentonite, from my understanding Alkaline Bentonites are used in brewing/wine industry however we do not currently sell into these markets/industries (at least locally) as our Trugel 100 is a sodium activated Bentonite normally used in civil applications, so I would suggest not suitable, I have attached tech data sheets for two products that are not Sodium activated but we cannot confirm or guarantee suitability for use in brewing/winery requirements or if food safe as we do not sell into these markets.I would suggest that this was a "protecting our backsides" response as the MSDS certainly implies it would be suitable, however my experiment indicates it is only marginally effective (100 gms of Bentonite with ~1 litre boiling water left to hydrate for 18 hours or so):
IMG_20180106_093722.jpg
IMG_20180106_093730.jpg
IMG_20180106_093911.jpg
IMG_20180107_113900[1].jpg
I expected the bentonite to settle out of the water but as you can see it remained in suspension.
I have no idea if I was doing things correctly though.
Later I poured off the cleared part of the wash and placed it into the fridge, it continued to clear and the bentonite "goobies" settled out even more but I find the merest of disturbances causes them to rise again and I have no reason to think this wouldn't happen at full scale as well.
Certainly, this experiment indicates that this particular bentonite is less effective than refrigerating - alas my refrigerator is not large enough for full scale use.
Back to the drawing board.
PS: the wash shown in the photos had already been left to settle in the fermenter for a week, then racked, then left for a further week - it still has loads of yeast in it.