Composite modification mechanism of cationic modifier to amphoteric modified kaolin and its effects on surface characteristics

In this study, the changes of S DC curves (sum amount of dodecyl trimethyl ammonium cation and Ca 2+ /2 adsorbed on dodecyl dimethyl betaine-modified kaolin under different dodecyl trimethyl ammonium cation molar fractions) were analyzed to reveal the modification mechanism of cationic modifier (dodecyl trimethyl ammonium bromide) on amphoteric modified kaolin (kaolin modified by dodecyl dimethyl betaine). In addition, total organic carbon content and surface characteristics of different modified kaolins were analyzed using X-ray diffraction, specific surface area calculation, Fourier transform infrared spectroscopy, thermogravimetry, and scanning electron microscope. Results showed that: (1) “ S DC ” curves of compositely modified kaolin with dodecyl dimethyl betaine-modified ratios of 15, 30 and 60 % started to rise (appeared hydrophobic binding) at dodecyl trimethyl ammonium bromide-modified ratios of 16.80, 7.63, and 0.68 % (the critical point for different modification mechanisms), respectively. (2) Total organic carbon content of modified kaolins under different modification mechanisms showed hydrophobic modification mode > ion exchange and hydrophobic binding coexisting mode > ion exchange mode. Interlayer spacing showed no significant change under different modification modes. Specific surface area decreased slowly with enhanced hydrophobic modification mode. Fourier transform infrared spectroscopy and thermogravimetry results showed the modification effects of both dodecyl dimethyl betaine and dodecyl trimethyl ammonium bromide modification on kaolin surfaces. Scanning electron microscope results presented that the number of lamellar structures increased on clay surfaces with enhanced hydrophobic modification mode.