152/154Eu(III) Ions Sorption on Stannic Silicate Granules: A Radiotracer Study
Chemical Science Transactions
Silicates and related porous materials are solids able to interact with guest molecules, ions and atoms not only at their surfaces but also within the bulk. With the objective of producing materials showing better sorption properties, a laboratory prepared stannic silicate in mixed SnO 2 @SiO 2 form was investigated as potential sorbent for retention of long lived radionuclides 152+154 Eu 3+ from aqueous solution containing 134 Cs + and 60 Co 2+ . Sorption of Eu 3+ has been reported as a
... n of contact time, initial ion concentration and temperatureat a constant pH equal to 4. The uptake of Eu 3+ was found to be favored at high ion concentration, high temperature and no significant sorption took place after the first 4 h. A pseudo second order kinetic pattern fitted the sorption data well, while equilibrium was positively verified with Freundlich-type equation. Further, in attempt to enhance the separation efficiency of the studied radionuclides from aqueous medium, results showed that the sorption on SnSi was found strongly temperature-dependent. Ions equilibrium was found exothermic in case of 134 Cs + however it endothermic in case of both 60 Co and 134 Cs ions. Based on this contradict uptake, selectivity of ions has been estimated and separation of Eu 3+ from other competing ions was achieved.The thermodynamic parameters (∆G•, ∆H• and ∆S•) showed that the adsorption process is spontaneous and exothermic in case of 134 Cs + but it endothermic in case of the later studied ions. Chem Sci Trans., 2019, 8(2),  134 Cs + and 60 Co 2+ isotopes are commonly present in radioactive wastes beside 152+154 Eu 3+ and owing to their relatively long half-lives (2.06, 5.27, 8.59 and 13.54y for 134 Cs + , 60 Co 2+ , 154 Eu 3+ and 152 Eu 3+ , respectively) as well as their radio-toxicity, these nuclides must be removed from wastes for safe discharge 3,4 . Europium as one metal belongs to the REEs is only stable in Eu 3+ in aqueous solutionand has used mainly in the manufacture of cathode ray tubes, fluorescent lamp and screen for x-rays. In nuclear industry europiumhas used as neutrons absorbent for the extinction and control rods of the reactors.Efficient separation of trace concentration fission products and other spent fuel constituents is necessary to enable various disposals or recycle options. Thus, the study of sorption kinetics in wastewater treatment is important in providing valuable insights into the reaction pathways and into the mechanism of adsorption reaction. Recently, adsorption as process for treating contaminated water has been object of several investigations because this method allows removal of a great amount of water polluting agents on several types of adsorbent materials; moreover, this method has shown to be economic and highly effective 5 . Adsorption can be defined as the accumulation of ions at the solid-liquid interface due to different types of forces.The sorption of 152+154 Eu(III) on clay minerals, metal oxides and nanomaterials had been extensively studied in the last decade 6-11 . The results suggested that the sorption of Eu(III) was strongly dependent on ionic strength and pH 6-11 . The sorption was mainly dominated by outer-sphere surface complexation and/or ion exchange at low pH, and by inner-sphere surface complexation and/or surface co precipitation at high pH values 6-11 . The removal of radioactive europium from nuclear waste solutions is important from the point of view of their toxicity and therefore has been of interest 12,13 . Among various types of inorganic ion exchangers available, silicates appears to be quite promising in the treatment of low-and high-level radioactive wastes 14-17 . Silicates have been reported to be important ion exchange materials as they are irradiation and temperature resistant 14-16 . The ion exchange properties of the H + form of crystalline stannic silicate, referred to as H-CSi indicate high ion selectivity 12,13,18 for 152+154 Eu 3+ . Adsorption isotherms developed from theoretical and/or empirical considerations are used to quantify such processes. This can be made by relating the solute concentration on liquid and solid phase at equilibrium condition.There are also many kinds of oxygen-containing functional groups such as Fe-OH, Al-OH, Si-OH and -OH groups on silicate surfaces, which can form strong surface complexes with metal ions and thereby can remove heavy metal ions from aqueous solutions efficiently. Fan et al 19, 20 ., studied sorption of Ni(II) and 152+154 Eu(III) on humic acid-bound attapulgte and found that humic acid could act as a "bridge" between metal ions and attapulgite. Ali et al., reported the synthesis and sorption mechanism of 22 Na, 134 Cs and 60 Co on stannic silicate(SnSi) 21 . In this paper, we evaluated the sorption behaviour of 152+154 Eu 3+ from aqueous nitratesolution onto SnSi granules as a function of concentration, time and temperature using radiotracer technique. Kinetic, sorption isotherm, thermodynamic and selectivity of Eu 3+ have been analyzed and discussed.