Selective immobilization of iodide onto a novel bismuth-impregnated layered mixed metal oxide: Batch and EXAFS studies

A novel Mg/Al/Bi ternary mixed metal oxide (MMO) was successfully prepared by a simple coprecipitation and calcination process. The Mg/Al/Bi MMO (molar ratio = 3:0.4:0.6) presented synergistically enhanced adsorption efficiency for iodide in water with porous structure. Kinetic adsorption results indicated good agreement with pseudo first-order-kinetic model (R = 0.998) and the maximum adsorption capacity calculated by Langmuir isotherm of Mg/Al/Bi MMO was 202.2 mg/g, which is higher than that of Mg/Al layered double oxide (LDO) (161.0 mg/g) and bismuth oxide (57.5 mg/g). In addition, the Mg/Al/Bi MMO showed good adsorption efficiency under neutral condition (pH 7), by which the material exhibits relatively strong resistance to the presence of co-existing anions in water due to the ion selectivity. Extended X-ray absorption fine structure (EXAFS) spectra revealed that the enhanced adsorption of iodide by Mg/Al/Bi MMO can be induced by selective Bi-O-IBformation, which is stable waste form for its treatment. Consequently, it is clear that the novel Mg/Al/Bi MMO is a potentially attractive material in terms of selective uptake of iodide with forming stable chemical complex in radioactive contaminants.

Enhanced removal of iodide ions by nano Cu2O/Cu modified activated carbon from simulated wastewater with improved countercurrent two-stage adsorption

A newly developed adsorbent nano Cu₂O/Cu-modified activated carbon composite (nano Cu₂O/Cu-C) was used to remove radioactive iodide ions (I^-) from simulated wastewater. The emphasis of this research is to improve adsorption performance and obtain higher I^- removal efficiency compared with the single-stage adsorption. To fully develop the amount of adsorption by nano Cu₂O/Cu-C, and to increase the decontamination factor (DF) of I^-, an improved countercurrent two-stage adsorption (ICTA) process was introduced. In the ICTA process, measures dealing with desorption of loaded adsorbent in the stage-two adsorption were taken and more extensive application of countercurrent two-stage adsorption (CTA) process could be made after the improvement to ICTA process in this study. Furthermore, in order to analyze the process and determine the I^- concentration in the effluent, a calculation method was devised based on the Langmuir isotherm equations and adsorption accumulation principle. The mean DFs were 177, 166, and 89.7, respectively, when the initial I^- concentrations were 5.00, 10.0, and 20.0 mg/L; and the adsorbent dosage was 1.25 g/L. These results were approximately 8.76, 8.97, and 6.79 times higher, respectively, than with conventional single-stage adsorption. The experimental values of the I^- concentration were higher than the calculated ones, which could be ascribed to desorption of the residual loaded adsorbent and formation of CuI in the adsorption at stage 1. Formation of CuI in the adsorption at stage 1 was considered to be the predominant reason.

Silver-Loaded Aluminosilicate Aerogels As Iodine Sorbents

In this paper, aluminosilicate aerogels were used as scaffolds for silver nanoparticles to capture I₂(g). The starting materials for these scaffolds included Na-Al-Si-O and Al-Si-O aerogels, both synthesized from metal alkoxides. The Ag⁰ particles were added by soaking the aerogels in aqueous AgNO₃ solutions followed by drying and Ag⁺ reduction under H₂/Ar to form Ag⁰ crystallites within the aerogel matrix. In some cases, aerogels were thiolated with 3-(mercaptopropyl)trimethoxysilane as an alternative method for binding Ag⁺. During the Ag⁺-impregnation steps, for the Na-Al-Si-O aerogels, Na was replaced with Ag, and for the Al-Si-O aerogels, Si was replaced with Ag. The Ag-loading of thiolated versus nonthiolated Na-Al-Si-O aerogels was comparable at ∼35 atomic %, whereas the Ag-loading in unthiolated Al-Si-O aerogels was significantly lower at ∼7 atomic % after identical treatment. Iodine loadings in both thiolated and unthiolated Ag⁰-functionalized Na-Al-Si-O aerogels were >0.5 m_I m_s^-1 (denoting the mass of iodine captured per starting mass of the sorbent) showing almost complete utilization of the Ag through chemisorption to form AgI. Iodine loading in the thiolated and Ag⁰-functionalized Al-Si-O aerogel was 0.31 m_I m_s^-1. The control of Ag uptake over solution residence time and [Ag] demonstrates the ability to customize the Ag-loading in the base sorbent to regulate the loading capacity of iodine.

Sorption and desorption studies of radioiodine onto silver chloride via batch equilibration with its aqueous media

The uncontrolled spread out of radioiodine (especially (1)(3)(1)I) produced from nuclear activities or accidents, due to its high volatility, to the biosphere represents an environmental impact because of its concentration in the thyroid gland and accumulation on soil surface. This work represents a simple method for isolation of radioiodine from aqueous solution in the form of insoluble solid compound and further recovery of it in aqueous phase for any further controlled use. Crystalline silver chloride was prepared and characterized. Batch sorption of (131)I onto the prepared AgCl was studied from different aqueous media (H2O and NaOH of different concentrations) and at different I(-):Ag molar ratios (from alkaline media) for different times at 25 °C. It was found that the sorption yield of (131)I from 2.5 M NaOH solution (at I(-):Ag and S2O3(2-):I(-) molar ratios of 0.025 and 2, respectively) reached 97.7% after 6 h and only slightly increased to 98.6% after 16 h of contact time. The presence of H2O2 adversely affected the batch sorption process. The included REDOX and precipitation reactions were discussed. Batch desorption of the sorbed (131)I from AgCl into aqueous phase was studied with NaOCl solutions of different concentrations and different contact times at 25 °C. Desorption yield of (131)I was found to be 94.5% with 10 mL of 0.5 M NaOCl solution after contact time of 16 h. Kinetic analysis has been performed for both batch sorption and desorption processes.