Aktivit Bentonite is a granuled calcium-sodium-bentonite for stabilization of fruit juices, grape juice and wine by adsorption of haze forming proteins and other colloids.
It is a fining product that can be added during fermentation or after fermentation. 
Holds a negative charge, so may be used in conjunction with a positive charge fining agent eg islinglass or sparkolloid.

Use 10g per 20litre / 5 gallon of homemade wine as finings for home winemaking.

Will not clear all hazes eg pectin hazes.

Highly absorbing, so protect from humidity & odours.

Before use, test odour in an aqueous (water) solution.

Rack your wine first.  Add & vigorously stir in a 15 times larger amount of cooled boiled water (ie for 10g use 150ml water). Leave to swell for 6 hours, stirring from time to time. Then add to must and shake or mix through. Once wine has cleared (may take anywhere from a few hours to 2 weeks), rack wine leaving behind the sediment.

See here for further info