Chrome chemicals are commercially produced by the alkali roasting of chromite ores with sodium carbonate. Results of tests conducted in a laboratory furnace indicated that the sodium carbonate reacted rapidly with part of the gangue material to form a metastable intermediate that later reacted further with the chromite. For the conditions used, the recovery of water-soluble sodium chromate was able to be described empirically as yield % =_x000D_
tn with_x000D_
= 0.24 T - 241.3; n = 3.90 - 3.12_x000D_
10-3 T and t is the reaction time in hours.The major rate limiting step in the overall reaction sequence appears to be the rate at which oxygen can get to the reaction sites across the liquid film coating the solid reactants.Sodium sulfate alone was found to be an unsatisfactory source of alkali for reaction with chromite. However when limestone also was added in quantities sufficient to allow the reaction CaCO3 + Na2SO4 + H20_x000D_
Ca SO4 + 2NaOH + CO2 to take place, the results obtained were comparable to those found when sodium car-bonate was used.For chromite particles in the size range -124 + 105 m, the use of stoichiometric excess of sodium carbonate did not appear to increase the yield or the reaction rate significantly. However, with smaller sized particles, - 53 m, increased yields of water-soluble chromate were obtained when roasted with more than the theoretical quantity of sodium carbonate.