Silylation of clay minerals from Cherkasy deposit (Ukraine) montmorillonite (layer silicate) and palygorskite (fibrous silicate) was performed using organosilane (3-aminopropyl)triethoxysilane (APTES). Solvents with different polarity (ethanol, toluene) were used in synthesis. The structure of modified minerals was characterized by complex of methods (X-ray powder diffraction, Fourier transform infrared spectroscopy, nitrogen adsorption-desorption at −196 °C and thermal analysis). Studies of adsorption characteristics of APTES-modified clay minerals were carried out in relation to uranium (VI). The results indicated that modified montmorillonite and palygorskite were effective materials for water purification from UO₂²⁺.

Zhovty Vody city, located in south-central Ukraine, has long been an important center for the Ukrainian uranium and iron industries. Uranium and iron mining and processing activities during the Cold War resulted in poorly managed sources of radionuclides and heavy metals. Widespread groundwater and surface water contamination has occurred, which creates a significant risk to drinking water supplies. Hydrogeologic and geochemical conditions near large uranium mine tailings storage facility (TSF) were characterized to provide data to locate, design and install a permeable reactive barrier (PRB) to treat groundwater contaminated by leachate infiltrating from the TSF. The effectiveness of three different permeable reactive materials was investigated: zero-valent iron (ZVI) for reduction, sorption, and precipitation of redox-sensitive oxyanions; phosphate material to transform dissolved metals to less soluble phases; and organic carbon substrates to promote bioremediation processes. Batch and column experiments with Zhovty Vody site groundwater were conducted to evaluate reactivity of the materials. Reaction rates, residence time and comparison with site-specific clean-up standards were determined. Results of the study demonstrate the effectiveness of the use of the PRB for ground water protection near uranium mine TSF. The greatest decrease was obtained using ZVI-based reactive media and the combined media of ZVI/phosphate/organic carbon combinations.

Low-cost sorption materials based on the clay mineral of the smectite group—montmorillonite—were used for the removal of radionuclides uranium (VI) and strontium (II) from contaminated water. A wide range of industrial methods such as thermal treatment, acid activation, and mechanochemical activation were applied. Complex methods, such as SEM microscopy analysis, X-ray powder diffraction (XRD), thermal analysis, and nitrogen adsorption–desorption at −196 °C, were used to assess the characteristics of the structure of the obtained materials. The thermal treatment, acid activation, and mechanochemical activation resulted in changes in the surface properties of the clay minerals: specific surface area, porosity, and distribution of active sites. It was established that the mechanochemical activation of montmorillonite significantly increases the sorption characteristics of the material for U(VI) and Sr(II) and the acid activation of montmorillonite increases it for U(VI). The appropriateness of the experimental adsorption values for U(VI) and Sr(II) on modified montmorillonite to Langmuir and Freundlich models was found. Independently of the changes induced by acid attack, calcinations, or milling, the sorption of U(VI) and Sr(II) ions on treated montmorillonite occurs on a homogeneous surface through monolayer adsorption in a similar fashion to natural montmorillonite. Water purification technologies and modern environmental protection technologies may successfully use the obtained clay-based sorbents.

The peculiarities of sorption removal of uranium (VI) compounds from the surface and mineralized groundwater using clay-supported nanoscale zero-valent iron (nZVI) composite materials are studied. Representatives of the main structural types of clay minerals are taken as clays: kaolinite (Kt), montmorillonite (MMT) and palygorskite (Pg). It was found that the obtained samples of composite sorbents have much better sorption properties for the removal of uranium from surface and mineralized waters compared to natural clays and nZVI.It is shown that in mineralized waters uranium (VI) is mainly in anionic form, namely in the form of carbonate complexes, which are practically not extracted by pure clays. According to the efficiency of removal of uranium compounds from surface and mineralized waters, composite sorbents form a sequence: montmorillonite-nZVI > palygorskite-nZVI > kaolinite-nZVI, which corresponds to a decrease in the specific surface area of the pristine clay minerals.

Clay minerals are widely used to treat groundwater and surface water containing radionuclides. In our study, the method of mechanochemical activation for increasing the sorption capacity of the natural clay mineral montmorillonite was used. By adjusting the grinding time, the increasing sorption parameters of mechanochemically activated montmorillonite were determined. X-ray diffraction method, scanning electron microscopy, and the determination of the specific surface by low-temperature adsorption–desorption of nitrogen to characterize the natural and mechanochemical-activated montmorillonites were used. It was established that the maximal sorption of uranium, strontium, and cesium is found for montmorillonite after mechanochemical treatment for 2 h. It is shown that the filling of the surface of montmorillonite with ions of different natures occurs in various ways during different times of mechanochemical treatment. The appropriateness of the Langmuir and Freundlich models for the sorption parameters of uranium, strontium, and cesium ions on montmorillonite after its mechanochemical activation was established. The effect of natural organic substances—humic acids—on the efficiency of water purification from uranium on mechanoactivated montmorillonite was studied. The obtained sorbents can be effectively used for the removal of trace amounts of radionuclides of different chemical natures (uranium, cesium, and strontium) from polluted surface and ground waters.