Process for the manufacture of a fine white filler for industrial purposes

A process for preparing ettringite or calcium trisulfoaluminate (3 CaO .sup.. Al.sub.2 O.sub.3 .sup.. 3CaSO.sub.4 .sup.. 32 H.sub.2 O) according to a reaction depicted by at least one of the following reaction schemes:

• a. CaO.sup.. Al.sub.2 O.sub.3 + 2(CaO.sup.. H.sub.2 O) + 3(CaSO.sub.4.sup.. 2H.sub.2 O) + 24H.sub.2 O .fwdarw. ettringite
• b. (CaO).sub.3 Al.sub.2 O.sub.3 + 3(CaSO.sub.4.sup.. 2H.sub.2 O) + 26 H.sub.2 O .fwdarw. ettringite
• c. CaO(Al.sub.2 O.sub.3).sub.2 + 5(CaO.sup.. H.sub.2 O) + 6(CaSO.sub.4.sup.. 2H.sub.2 O) + 47H.sub.2 O .fwdarw. 2 ettringite
• d. 12 CaO.sup.. 7Al.sub.2 O.sub.3 + 9(CaO.sup.. H.sub.2 O) + 21(CaSO.sub.4.sup.. 2H.sub.2 O) + 173H.sub.2 O .fwdarw. 7 ettringite
• e. CaO.sup.. 6Al.sub.2 O.sub.3 + 17(CaO.sup.. H.sub.2 O) + 18(CaSO.sub.4.sup.. 2H.sub.2 O) + 139H.sub.2 O .fwdarw. 6 ettringite
• which comprises forming a substantially stoichiometric mixture of calcic aluminate and calcium sulfate in an amount of water which is at least a stoichiometric proportion and at most sufficient to yield a product containing 5 percent by weight of (dry) ettringite and 95 percent by weight of water, and effecting reaction at a temperature in the range of from 20.degree. to 90.degree. C;
• the calcium sulfate having as white a color as possible, and the stoichiometric mixture and the stoichiometric proportion being based on the reaction.