Thermal decomposition behaviour of polyacrylamidomethyltrimethyl ammonium chloride in red mud separation process

Abstract

In order to provide references for selecting highly efficient red mud flocculants, the behaviour of polyacrylamidomethyltrimethyl ammonium chloride (PATAC) in red mud separation process was investigated. PATAC was employed as a flocculant for red mud separation from the caustic aluminate liquor at 95 °C. The used red mud was generated from Chinese diaspore bauxite in Bayer process of alumina production. And the changes of PATAC before or after being treated in caustic solution at 95 °C were studied by thermogravimetry (TG) and Fourier transform infrared (FTIR) spectral analysis. The results show that PATAC fails in effectively flocculating red mud and PATAC is readily converted to a quaternary ammonium hydroxide (PATAH) in caustic solution. PATAH can be decomposed to a new polymer (HPATAH) even at 95 °C. Furthermore, there is an intramolecular hydrogen bond formed in the HPATAH polymer chain with two functional groups of -CH2-OH and -CONH2. Therefore, the poor flocculation property of PATAC for red mud separation can be attributed to the thermal decomposition of PATAC in the caustic red mud slurry at 95 °C and the formation of intramolecular hydrogen bond in the polymer chain of HPATAH during the thermal decomposition, which causes the absorbable functional groups of PATAC to decrease greatly.