Production of low-sulfur chromium (III) oxide pigment

Abstract

In the continuous production of low-sulfur chromium(III)oxide pigment comprising the steps of reducing a finely divided alkali metal chromate in a heated hydrogen-containing reaction zone at a temperature of about 900.degree. to 1600.degree. C, and precipitating the resulting chromium(III)oxide in the form of an aqueous dispersion, the improvement which comprises passing the reduction products from the reaction zone to a dwell zone and generating heat within said dwell zone to maintain the temperature therein in the range of about 900.degree. to 1600.degree. C. Preferably the dwell zone temperature is within 200.degree. C of that in the reaction zone and is maintained by introducing excess hydrogen into the reaction zone and consuming it in the dwell zone by introduction of oxygen. The resulting pigments exhibit a fuller green color.

Dependencies are inferred from the claim text.