Experimental Study of Montmorillonite Structure and Transformation of Its Properties under Treatment with Inorganic Acid Solutions

Victoria Krupskaya,Petr Belousov,Ekaterina Tyupina,Anatoliy Zhukhlistov,Maria Timofeeva,Sergey Zakusin,Olga Dorzhieva

doi:10.3390/min7040049

Abstract

This paper discusses the mechanism of montmorillonite structural alteration and modification of bentonites’ properties (based on samples from clay deposits Taganskoye, Kazakhstan and Mukhortala, Buriatia) under thermochemical treatment (treatment with inorganic acid solutions at different temperatures, concentrations and reaction times). Treatment conditions were chosen according to those accepted in chemical industry for obtaining acid modified clays as catalysts or sorbents. Also, more intense treatment was carried out to simulate possible influence at the liquid radioactive site repositories. A series of methods was used: XRD, FTIR, ICP-AES, TEM, nitrogen adsorption, and particle size analysis. It allowed revealing certain processes: transformation of montmorillonite structure which appears in the leaching of interlayer and octahedral cations and protonation of the interlayer and –OH groups at octahedral sheets. In turn, changes in the structure of the 2:1 layer of montmorillonite and its interlayer result in significant alterations in the properties: reduction of cation exchange capacity and an increase of specific surface area. Acid treatment also leads to a redistribution of particle sizes and changes the pore system. The results of the work showed that bentonite clays retain a significant portion of their adsorption properties even after a prolonged and intense thermochemical treatment (1 M HNO3, 60 °C, 108 h).

Highlights

Clay minerals are widely used in various industries including radioactive waste management as a component of barrier systems for waste disposal
These particularities of montmorillonite structure determine specific properties of bentonite clays, especially high adsorption capacity towards heavy metals such as cesium, plutonium etc., which are commonly found in radioactive wastes
A variety of processes that modified structure and properties montmorillonite particlesparticles were observed during during the treatment with inorganic acid solutions: dissolution of montmorillonite were observed the treatment with inorganic acid solutions: of carbonates and feldspars,and destruction the mostofdefective phases phases (e.g., nanosized dissolution of carbonates feldspars, of destruction the most phyllosilicate defective phyllosilicate, removal of cations from the interlayer spacing, substitution of interlayer smectites), removal of cations from the interlayer spacing, substitution of interlayer cations with cations with oxonium leaching of the octahedral cations, the andcomplete thedestruction complete destruction of oxonium ion, leaching of ion, the octahedral cations, and of the structure

Summary

Introduction

Clay minerals are widely used in various industries including radioactive waste management as a component of barrier systems for waste disposal. Layer charge is compensated by the introduction of exchangeable interlayer cations (Na+ , Ca2+ , Mg2+ , etc.) usually in hydrated form [4,5,6,7,8] which in turn provides adsorption sites on the inner and outer surface of the crystal. These particularities of montmorillonite structure determine specific properties of bentonite clays, especially high adsorption capacity towards heavy metals such as cesium, plutonium etc., which are commonly found in radioactive wastes

Objectives

Methods

Results

Conclusion