The work is devoted to the development on the basis of the evolution of physico - chemical ideas about the mechanism of sorption processes of the system approach to purposeful regulation of sorption properties of layer silicates at their modification for the purpose of removal of heavy metal compounds and radionuclides. The use of the obtained organophilized, pillared and modified by particles of nanosized iron layered silicates in the treatment of surface, groundwater and wastewater of various types contaminated water with heavy metals and radionuclides is proposed.
The determining role of surface chemistry of layer silicates (type and concentration of active sorption centers on basal and side faces) in the formation of the structure of the modifying surfactant layer has been established.
Peculiarities of selective sorption of anionic forms of uranium and chromium have been studied on the surface of siliceous material diatomite, layer silicates - montmorillonite and paligorskite, which are modified by cationic surfactant hexadecyltrimethylammonium bromide (HDTMA). The main stages of surface modification of layer silicates by cationic surfactants are determined. The relationship between the structure of the surfactant surface layer of organophilized silicates and the sorption values of cationic and anionic forms of heavy metals and radionuclides has been revealed. It is shown that a significant increase in the sorption values of uranium and chromium compounds from both mineralized and surface waters occurs with an increase in the surfactant content when modifying the surface of layered silicates.
The properties of layer silicates modified with cationic surfactants and organosilane 3-aminopropyltriethoxysilane (APTES) were compared and the influence of the type of modifier bond with the silicate matrix surface on the sorption values was shown.
Physico-chemical features of interaction of layered silicates with polynuclear and heteropolynuclear hydroxocomplexes of metals, which are intercalated in the interlayer space of minerals, are analyzed. It is shown that the structural characteristics of pillar montmorillonite depend on the composition of polyhydroxocomplexes in the interlayer space of the mineral.
It is shown that adsorption on such materials can be considered as on hydroxides or hydrated oxides of the corresponding metals, where the active (sorption) centers will be hydroxyl groups on the surface of the pillared clay minerals. The regularities of selective sorption of cobalt , chromium and uranium ions from aqueous solutions are established and the influence of pH and mineralization of initial solutions on the course of these processes is characterized. It has been established that pillared montmorillonite has mainly anion exchange properties, so the anionic forms of uranium , which predominate in mineralized waters, are selectively removed by samples of pilar bentonite. A series of sorption capacity of pilar clays in mineralized waters with respect to uranium compounds Ti> Fe> Zr> Al was obtained. The main ways to increase the selectivity of pilated swellable layer silicates of the smectite type in relation to the cationic forms of heavy metals and radionuclides are substantiated. High sorption characteristics of pillar montmorillonite Al-Fe, Ti-Fe, Al-Zr, Ti-Al determine the prospects of their use as adsorbents and catalysts.
At first time, an increase in the sorption properties of iron nanoparticles immobilized on the surface of dispersed minerals relative to heavy metals and radionuclides was established.
The role of the complex “core – shell”– structure of iron nanoparticles immobilized on the surface of layer silicates in the processes of sorption - reduction of chromium and uranium ions is analyzed. An assessment of the contribution of both components to the overall process of removal of these ions from solutions is given.
Dispersed zero-valent iron was used in the construction of an active reactive barrier to protect groundwater from contamination by uranium compounds in the center of the uranium industry of Ukraine – the Zhovti Vody city at the Eastern Mining and Processing Plant. The barrier was built on the way of polluted groundwater to the Zhovta River near the largest existing tailings pond with waste sulfuric acid processing of uranium ores at the hydrometallurgical plant. The effectiveness of the barrier to uranium compounds based on environmental monitoring for two years were established.
Purposeful regulation of surface properties of layer silicates which modified by various methods expands the area of application of new sorption materials for treatment of surface, groundwater and wastewater of various types contaminated with heavy metals and radionuclides.
Key words: sorption, uranium, heavy metals, selectivity, layer silicates, surface modification, zero valent iron, pillarding, surfactants, mineralized waters.
