“…Explanations: 1 = Surface -OH stretching vibration of kaolinite, 2 = Surface -OH stretching vibration of kaolinite, 3 = Surface -OH stretching vibration of kaolinite, 4 = Inner surface -OH stretching vibration of kaolinite, 5 = H-O-H stretching vibrations of water within montmorillonite, 6 = Quartz, 7 = Quartz, and feldspar, 8 = Surface -OH bending vibration of kaolinite, 9 = Inner surface -OH bending vibration of kaolinite, 10 = Si-O-Si inter-tetrahedral bridging bonds of SiO2, 11 = Si-O-Si inter-tetrahedral bridging bonds of SiO2, 12 = Surface -OH bending vibration of kaolinite, 13 = -OH bending vibration of montmorillonite. Peaks are assigned following the works ofDjomgoue and Njopwouo (2013),Saikia and Parthasarathi (2010) andVarma et al (2018).…”