In English

Abstract

Introduction shows the important of this scientific direction. 60 Co with half-life of 5.3 years is one of the few anthropogenic, gamma-emitting radionuclides, that can be detected in aquatic environments affected by liquid effluent discharged from nuclear facilities. The need for control of the content of 60 Co in the environment, determines the search for new adsorption materials with high adsorption capacity and chemical, thermal, and radiation resistance. The aim of present work is to investigate the adsorption of Co 2+ and 60 Co by mesoporous TiO 2 from aqueous solutions. Experimental techniques describes the adsorption studies in detail. The mesoporous TiO 2 with the initial pore size ratio (S meso /S = 58 %; V meso /V = 64 %) was selected as adsorbent. Synthesis of adsorbents was carried out by the method of liquid phase hydrolysis of aqua complex of TiCl 4 . The dependence of adsorption value on agitation time, solutions acidity, and equilibrium concentration of Co 2+ was investigated in butch mode. The presence of cobalt on the surface of mesoporous TiO 2 was confirmed using XRF-analysis. The initial and residual concentration of cobalt was controlled by complexonometric titration with xylenol orange as indicator. Four simplified kinetic models: pseudo-first order and pseudo-second order equations, firstly applied by Lagergren, intraparticle diffusion and Elovich (Roginsky-Zeldovich) kinetic models were applied to experimental data. Langmuir and Dubinin-Radushkevich adsorption theory applied for experimental equilibrium data of adsorption of cobalt cations by mesoporous TiO 2 . The adsorption energy was measured using Dubinin-Radushkevich equation. The results obtained have shown that the experimental data on the adsorption kinetics of Co 2+ by mesoporous TiO 2 fit well by Lagergren pseudo-second kinetic model. Applying of Elovich kinetic model gives also high correlation’s coefficients, close to unit (R 2 > 0.9). The equilibrium adsorption data are well approximated by Langmuir adsorption theory. Maximal adsorption value obtained experimentally (49±4 mg/g) is in good agreement with calculated by Langmuir adsorption theory (63.81 mg/g). The adsorption energy calculated using Dubinin-Radushkevich equation is 8.104±0.361 kJ/mol, which correspond to physical adsorption mechanism. However, for each values of Polanyi’s potential (ε) (which correspond to certain equilibrium concentration C e , mg/L) adsorption energy is different. It smooth decreases with increasing concentration of adsorbate in the solution. Although the experimental results are well describing by the Langmuir model, the adsorption energy of Co 2+ ions by mesoporous TiO 2 depends on the degree of surface filling, which means that the adsorption centers of this sample are not independent. At the low equilibrium concentration of Co 2+ (38 mg/L), the adsorption energy is much higher than the corresponding value for adsorption by the physical mechanism. To our opinion, that is why applying of Elovich kinetic model to experimental dada gives high R 2 . The adsorption of Co 2+ by mesoporous TiO 2 strongly depends on solutions acidity. To simulate conditions close to real, the adsorption of 60 Co by mesoporous TiO 2 was investigated. The percentage of 60 Co, adsorbed onto TiO 2 is more than 90 %. The main conclusion is that mesoporous TiO 2 could be useful as an adsorbent for water purification from Co 2+ and in decontaminating of radioactive waste containing 60 Co.