ИСТИНА

Montmorillonite clays are characterized by a high sorption capacity and can be used as a component of engineered barrier systems for radioactive waste disposal. The aim of this research is to assess the mechanism of transformation affecting the montmorillonite structure and its adsorption properties in processes that imply longterm interaction with nitric acid solutions. The aim of this study is to describe features of structure and surface properties modification of different industrial Russian bentonite clays as a result of treatment with a nitric acid solution at an elevated temperature. Features of the composition and structure of natural and modified bentonite samples were studied with a set of methods (XRD, SEM, XRF, etc). Specific surface area and cation exchange capacity values were determined to characterize the adsorption properties. Staging transformation of the structure of montmorillonite under the influence of acid treatment was described. It was revealed that treatment with HNO3 solutions results in partial leaching of interlayer and octahedral cations, which leads to protonation of internal surfaces, as well as the increasing microporosity due to partial degradation of the structure caused by the protonation of octahedral OH-groups followed with changing of the octahedral Al coordination and overall leaching of octahedral cations. The result of exposure to acid solutions is the reduction of the layer charge and modification of interactions between layers and sheets, and as a consequence, partial destruction of particles, which leads to a significant increase of the specific surface area. Whereas in contrast, with an increasing treatment duration, cation exchange capacity values decrease due to reduction of the layer charge.