QUATERNARY AMINES AS SODIUM OXALATE SEED STABILIZERS IN BAYER LIQUOR
Sipos, G. Shaw, M. Seydel, U. Parkinson, G. Smith, P. Kildea, J.
Sodium oxalate is one of the many organics present in Bayer liquor. Due to its limited solubility, sodium oxalate can co-precipitate with alumina trihydrate during precipitation. This can have detrimental effects on the final product quality especially if it occurs in the initial stages of precipitation.
Quaternary amine type cationic surfactants can prevent sodium oxalate co-precipitation and increase the tolerable concentration of sodium oxalate in Bayer liquor. Their action is via the inhibition of nucleation or/and the inhibition of crystal growth. This paper presents work detailing the effect of quaternary amines on sodium oxalate crystal growth in Bayer liquor.
The results show that while quaternary amines inhibit crystal growth in Bayer process liquors, they have no effect on crystallization in synthetic liquor. It is postulated that the presence of certain organic molecules in the process liquor are required for quaternary amines to inhibit crystallization and therefore stabilize the liquor. Humic material obtained from Bayer liquor has been shown to be effective in this role. Commercial humic acids have been tested and compared with plant humates.
Adsorption isotherms of octyltrimethylammonium bromide (OTAB) and plant humates have been successfully measured in Bayer liquor. Investigations with OTAB and plant humates reveal a synergy between the two. From a mixture of quaternary amine and plant humates, an enhanced adsorption of both components was observed. Confocal laser scanning microscope (CLSM) images of plant humates adsorbed on sodium oxalate crystals are also presented.