Separation and characterisation of montmorillonite from a low‐grade natural bentonite: using a non‐destructive method

Abstract

Bentonite clays containing mostly montmorillonite as a nanostructure group of smectite have been used as industrial raw material in many applications. The presence of the other impurities in bentonite clays reduces the value of bentonite. Therefore, the bentonite purification is necessary. In this research, the purification and separation of montmorillonite from a low-grade natural bentonite were considered on the regular and comprehensive plan. For this purpose, a set of methods including dispersion, sodium-activation, sedimentation, sonication and centrifugation were used. In contrast to many methods, there were often complex, expensive and non-effective; this purification method was found to be effective for removing almost all quartz, carbonates and clinoptilolite as the major impurities. In this purification method, the montmorillonite content was increased from 15 to 84% with the separation yield of 80%. The influence of centrifugal force and the type of ultrasonication indicated the most critical parameters in the purification yield, the physical properties and the crystalline structure of the final products. The laser particle size distribution analysis, X-ray diffraction, semi-quantitative analysis and Fourier-transform infrared spectroscopy results showed the decrease of impure phase without any structural changes or damages in clay framework.