Quantitative methods for quantification of montmorillonite content in bentonite clays

Abstract

This article is devoted to the comparison of various methods for the quantitative determination of montmorillonite content in bentonite clays based on the adsorption of organic molecules and cations. The studies were conducted on samples of natural bentonite clays of the main Russian industrial deposits and the CIS: 10th Khutor (Republic of Khakassia), Zyryanskoe (Kurgan region), Dash-Salakhlinskoe (Republic of Azerbaijan), Dinozavrovoe (Republic of Kazakhstan). All samples selected for the study are characterized by a high content of montmorillonite (more than 70 %). As reference values ​​for the contents of montmorillonite, we used the data of X-ray diffraction analysis according to the Rietveld method. As the tested methods, the most common approaches were used both in the research and industrial sectors of Russia, based on the adsorption of a mixture of rhodamine 6zh and chrysoidine dyes (GOST 28177-89), adsorption of methylene blue dye and adsorption of copper (II) complex with triethylenetetramine (Cu-trien), as well as thermal characteristics after saturation with organic compounds. The best convergence of the montmorillonite content values ​​was shown by modified techniques based on the adsorption of methylene blue dye and the adsorption of the Cu-trien complex. Other methods are characterized by a large measurement error. A common problem with these methods is overs equivalent adsorption on highly charged alkaline bentonites and reduced adsorption on alkaline earth bentonites, as well as the presence of impurity minerals and amorphous phases capable of sorption in the composition of bentonite. The research results can be used to compare the results of the content of montmorillonite, cited by various authors in scientific publications and used in production.