THERMAL IMMOBILIZATION OF Cr(VI) AND Co(II) FROM SPENT NANOCOMPOSITE SORBENTS IN A HYDROMICA CERAMIC MATRIX

Abstract

The issue of safe management of spent adsorbents saturated with toxic ions remains one of the most complex challenges in modern environmental protection technologies. This study investigates the patterns of thermal transformation of a spent multicomponent sorbent based on organo-modified montmorillonite with surface-deposited nanoscale zero-valent iron (nZVI) after the removal of chromium (Cr(VI)) and cobalt (Co(II)) ions from aqueous solutions. To ensure reliable localization and prevent secondary migration of toxic species, a high-temperature ceramic immobilization technology is proposed. The spent sorbent was introduced into a natural hydromica matrix at 20 %, acting as an effective plasticizer and a source of alkali fluxes, followed by plastic shaping and heat treatment across the 700-1000 ºC temperature range. Using a comprehensive combination of X-ray diffraction (XRD) and thermal analyses, the character of structural and phase transformations was established. It was proven that optimal liquid-phase sintering conditions are achieved at a temperature of 900 ºC, yielding a dense ceramic structure with a maximum compressive strength of 34.5 MPa and a minimum open porosity of 0.8. The primary mechanisms of micro-encapsulation and fixation of heavy metals involve the migration of pollutant ions into the subsurface layers of the aluminosilicate matrix with incorporation into vacant polyhedra of the framework, as well as high-temperature spinel formation. Leaching kinetics studies on pelletized samples in aqueous and aggressive media confirmed the high chemical stability of the obtained matrices and the reliable blocking of secondary pollutant migration. These results demonstrate the high efficiency and ecological feasibility of using hydromica-based ceramic technology for the ultimate disposal of hazardous water treatment wastes.