GB1038773A - Improvements relating to the production of chromic oxide - Google Patents

Abstract

<PICT:1038773/C1/1> In a process for the production of Cr2O3, an aqueous solution of a thermally decomposable chromium compound is dispersed in a stream of hot combustion gas. The heat required for the thermal decomposition is generated by combustion of liquid or gaseous fuel in the gas stream. Alternatively, the gas stream may be incompletely burnt to obtain reducing conditions and further oxygen or air may be introduced after the Cr2O3 has been formed. Further combustion material may also be introduced into and burnt in the gas stream after formation of Cr2O3. A minor proportion of a colour modifying compound may be included in the make solution of chromium compound. The Cr2O3 formed may be recovered by scrubbing with H2O. Using the apparatus of Fig. 1, a 60% aqueous solution of chromic acid in vessel 1 and paraffin in vessel 2 were mixed in vessel 7, to obtain 80% by weight of chromic acid solution and 20% paraffin. The mixture was injected into the spray head 10 at 0.2 litres per min. and 40 p.s.i., air being introduced via line 12. The spray passes through the burner 16 where thermal decomposition occurs. Reducing conditions were obtained by restricting the air supply by valve 13 so that the paraffin was not fully burnt. The flame temperature was about 900 DEG C. The combustion was completed by air drawn in post burners 19 and 20. The Cr2O3 which collected in vessel 23 was scrubbed with water introduced by spray nozzles 26 and withdrawn as an aqueous slurry at 27. It was fine enough to use as a pigment without grinding.