Interactions between specific organic compounds during catalytic wet oxidation of Bayer liquor

The catalytic wet oxidation (WO) mechanisms for the salts of organics, particularly carboxylic acids, in highly alkaline solution are of prime importance from the viewpoint of alumina producers because organic contaminants have adverse effects on the alumina refining process. Four organic compounds of interest, which are found in several worldwide alumina process liquors (Bayer liquor), are sodium acetate, oxalate, malonate, and succinate. CuO-catalyzed WO of the aforementioned organic salts was studied in an alumina process liquor (Bayer liquor) and synthetic Bayer liquor. CuO was found to catalyze the WO of only one of the organic salts, sodium malonate, in isolation in synthetic Bayer liquor at low temperature (165degreesC). In Bayer liquor, however, both sodium malonate and sodium succinate underwent CuO-catalyzed WO at 165degreesC. Sodium succinate was found to undergo CuO-catalyzed WO at 165degreesC in Bayer liquor via a co-oxidation mechanism. Sodium malonate was identified as a compound capable of co-oxidizing sodium succinate under Bayer-like (highly alkaline) conditions. Sodium malonate was also found to be capable of co-oxidizing sodium acetate under Bayer-like conditions, indicating that highly reactive free-radical intermediates are formed during CuO-catalyzed WO of sodium malonate.