Diferenciação catiônica de bentonitas por infravermelho: um estudo dos efeitos da hidratação dos cátions trocáveis

Abstract

In the bentonite industry, the most common procedure for quality control of the ore and the sodium activation process is the swelling method. However, this tool is restricted only to the differentiation of the sodium and non-sodium types, not considering the other cationic varieties. The analysis of the composition of exchangeable cations requires laborious procedures, with daily cationic exchanges (between 3 and 6 days) and chemical analysis Via Humid, which would be unfeasible for this type of industry. Despite this, knowledge of the cationic type is of paramount importance, as it would help in the implementation of a technological route of better quality and efficiency of sodium activation. In this context, he sought in this work to establish cationic differentiation parameters for bentonites based on near and medium infrared spectroscopy for the investigation of hydration of exchangeable cations. Particle size distribution (DTP) and N2 BET adsorption-desorption isotherms were also used. Eleven smectites were studied, including one Mg-montmorillonite and two from the Clay Minerals Society repository: SWy-2 (Na-montmorillonite) and SAz-1 (Ca-montmorillonite). The clay fraction obtained by granulometric separation was characterized by FRX, DRX, CTC and PCZ. Previous heat treatment by drying at 105 ºC for 24 h and dehydration at 400 ºC for 2 h. Exchangeable cations and hydration influenced the absorption bands of water molecules in the near and medium spectral region, showing that they are strongly influenced by the size and charge of the ions (monovalent and divalent). The cationic differentiation was observed by the intensity of these bands. Absorptions close to 3620 cm-1 were attributed to water directly linked to cations, however, differentiation was only possible in samples dried at 105 ºC, because at this temperature they still remain hydrated. The reduction in the intensity of this band is due to the decrease in the water content, due to dehydration of the interlayer after heating to 400 ºC, which does not favor differentiation. The absorptions close to 3430 cm-1 were attributed to the adsorbed water molecules, as well as the complex band in 7072 cm-1, obtaining a spectrum, in descending order, Ca, Mg and Na. DRIFT spectroscopy in the nearby region was considered a simple, fast and low-cost analysis technique that allowed to distinguish different types of bentonites.