Process for the preparation of thermostable black and brown pigments and

Abstract

A process is disclosed for the preparation of black and brown thermostable pigments consisting essentially of mixed phases of iron and manganese oxides, characterized in that: (a). pyrolusite, in the form of particles having a mean diameter not exceeding 20 microns, is mixed and maintained in contact together with heptahydrated ferrous sulphate at a temperature between room temperature and 95.degree. C.; and (b). the mass thereby obtained is dried, crushed and screened, and then calcined in the presence of air in a fluidized bed reactor at a temperature between 800.degree. and 900.degree. C. The starting pyrolusite/heptahydrated ferrous sulphate mixture may be additioned with one or more compounds selected from the group consisting of FeCl.sub.2, SiO.sub.2, FeCl.sub.3, Na.sub.2 SiO.sub.3, Fe.sub.3 O.sub.4, NaAlO.sub.2, KAl(SO.sub.4).sub.2 and NaBO.sub.2. The total quantity of additives is between 0.5% and 5% by weight based on the final product. The starting pyrolusite/heptahydrated ferrous sulphate mixture may also be additioned with water in a quantity not exceeding 20% by weight. The residence time of the solids in the fluidized bed reactor is between 1 and 6 hours. The black and brown thermostable pigments obtained from the process are also claimed.