Aluminophilicity of the Humic Degradation Product 5-Hydroxybenzene-1,3-dicarboxylic Acid

The humic substances in Bayer liquor (the sodium hydroxide soluble part of bauxite in alumina refinery plants) precipitated with the aluminum hydroxide cake at pH 7 have been studied. Five types of organic carbon were found by solid-state 13C nuclear magnetic resonance, corresponding to alkyl (24.9 ppm), alcoholic (81.1 ppm), aromatic (137.3 ppm), oxalate (164.8 ppm), and carboxylate (183.4 ppm) functionalities. Gas chromatography/mass spectrometry was also used to study the adsorbed organics. An interesting finding was the detection and prominence of 5-hydroxybenzene-1,3-dicarboxylic acid, yet it had no effect on sizing or alumina trihydrate yield. Thus, there appears to be no correlation of adsorbivity on aluminum hydroxide with inhibition of crystallization. The results assist in the understanding of the mechanism of activity of hydroxy organic compounds as aluminum hydroxide poisons in the Bayer precipitation process.