Abstract: Process for preparing ammonium dichromate, comprising the steps of c) thermally decomposing an alkali metal ammonium chromate double salt, especially a sodium ammonium chromate double salt or hydrates thereof, at a temperature up to 200° C., especially of 75 to 190° C., to form ammonium dichromate and d) removing the ammonium dichromate from the decomposition product obtained after step c), by crystallization, characterized in that the alkali metal ammonium chromate double salt corresponds to the formula Mx(NH4)yCrO4 or hydrates thereof, in which M is Na or K, particular preference being given to Na, x is from 0.1 to 0.9, preferably from 0.4 to 0.7, y is from 1.1 to 1.9, preferably from 1.3 to 1.6, and the sum of x and y is 2.

Abstract: Process for preparing chromium(III) oxide, comprising the steps of: a) Decomposing an alkali metal ammonium chromate double salt at a temperature of 200 to 650° C., especially of 250 to 550° C., b) washing the decomposition product obtained after a) and c) calcining the product obtained after b) at a temperature of 700 to 1400° C., especially of 800 to 1300° C.