Influence of the purity of montmorillonite on its surface modification with an alkyl-ammonium salt

Abstract Effect of the purity of montmorillonite (Mt) on its modification with hexadecyltrimethylammonium bromide (HDTMA) was evaluated. Montmorillonite with different grades of purity were prepared using two strategies: size fractionation (physical purification) and combination of chemical dissolution of some impurities and size fractionation (chemical–physical purification). It was found that the physical purification separated some impurities while chemical–physical purification separated almost all impurities from the montmorillonite. The cation exchange capacity (CEC) of the montmorillonite was increased after purification; this increase was much higher for samples that underwent chemical–physical purification, in comparison to those purified only with size fractionation. After modification of the montmorillonite with different grades of purity at the same ratio of HDTMA/CEC, different XRD patterns were obtained. For the modified raw and physically purified montmorillonite the 001 reflection of the XRD spectra were broad ranging between 15 and 18 Ǻ, and for the purer montmorillonite, after the modification with HDTMA the XRD spectra showed very much sharper diffraction peaks at d values of 14.7 and 17.4 Ǻ. The DTG results showed that the HDTMA was adsorbed in the interlayer spaces as HDTMA-Br molecules or HDTMA + cations. It was concluded that the form of adsorption of HDTMA either as HDTMA-Br molecules or HDTMA + cations is related to the arrangement of charges on the montmorillonite layers which can be altered during its chemical purification process.