A Convenient Procedure for the Acidic Activation of Mineral Bentonite: An Environmentally Friendly Method for the Preparation of Bleaching Earths

Refluxing montmorillonite-containing raw bentonite ((Na,Ca)o.33(Al,Mg)2Si 4 O 10 (OH) 2 ) in aq HNO 3 , then neutralizing it with NH 3 produces NH 4 NO 3 -containing NH 4 -bentonite. The NH 4 NO 3 intercalated can be eliminated as a gaseous product (N 2 O and H 2 O) by heating at 400 °C, and the deammoniation and dehydroxylation process of the preactivated bentonite leads to formation of bleaching earth (H x (Al,Mg) 2 -ySi 4 O 10 -(OH) 2 ).