Radioactivity/Radionuclide (U-232 and Am-241) Removal from Waters by Polyurea-Crosslinked Alginate Aerogels in the Sub-Picomolar Concentration Range

Abstract

The removal of radionuclide/radioactivity from laboratory and environmental water samples under ambient conditions was investigated via batch-type experiments using polyurea-crosslinked calcium alginate (X-alginate) aerogels. Water samples were contaminated with traces of U-232 and Am-241. The removal efficiency of the material depends strongly on the solution pH; it is above 80% for both radionuclides in acidic solutions (pH 4), while it decreases at about 40% for Am-241 and 25% for U-232 in alkaline solutions (pH 9). This is directly associated with the presence of the radionuclide species in each case; the cationic species UO22+ and Am3+ prevail at pH 4, and the anionic species UO2(CO3)34– and Am(CO3)2− prevail at pH 9. Adsorption on X-alginate aerogels is realized by coordination of cationic species on carboxylate groups (replacing Ca2+) or other functional groups, i.e., –NH and/or –OH. In environmental water samples, i.e., ground water, wastewater and seawater, which are alkaline (pH around 8), the removal efficiency for Am-241 is significantly higher (45–60%) compared to that for U-232 (25–30%). The distribution coefficients (Kd) obtained for the sorption of Am-241 and U-232 by X-alginate aerogels are around 105 L/kg, even in environmental water samples, indicating a strong sorption affinity of the aerogel material for the radionuclides. The latter, along with their stability in aqueous environments, make X-alginate aerogels attractive candidates for the treatment of radioactive contaminated waters. To the best of our knowledge, this is the first study on the removal of americium from waters using aerogels and the first investigation of adsorption efficiency of an aerogel material at the sub-picomolar concentration range.

The Interaction of Two Emerging Pollutants, Radionuclides and Microplastics: In-Depth Thermodynamic Studies in Water, Seawater, and Wastewater

“…The higher Kd values associated with the oxidized biochar can be ascribed to the higher chemical affinity of the carboxylic groups, which are present on the biochar's surface towards the hard Lewis acids (e.g., Am 3+ and UO2 2+ ). In addition, high Kd values have been determined also for the adsorption of the Am(III) and U(VI) isotopes by X-alginate aerogels [44]. The Kd values determined in the present study are closer to corresponding Kd values determined for the adsorption of the same radionuclides by PN6 and PE microplastics.…”

Actinide Ion (Americium-241 and Uranium-232) Interaction with Hybrid Silica–Hyperbranched Poly(ethylene imine) Nanoparticles and Xerogels

“…In the neutral and alkaline pH region (due to the extremely low actinide concentration), the actinide complexation may occur directly with the partially de-protonated amino groups [ 67 ]. In the case of uranium (e.g., uranyl moiety), interaction of the uranyl oxygens and ammonium protons is also possible, favoring surface binding of U(VI) ( Figure 2 ) [ 6 , 7 ].…”

“…Specifically, the % relative removal decreases with increasing pH, and at pH 9 the values of the relative removal are below 50%. To understand this behavior, we must take into account the predominant radionuclide species at each pH and their charges in conjunction with those of the adsorbents [ 7 ]. At low pH levels, the predominant ion species (Am 3+ , UO 2 2+ ) are positively charged and electrostatically rappelled by the homonymous charges of both adsorbents.…”

“…Moreover, the data indicate that both materials present a higher affinity for U(VI) compared to Am(III). Compared to alginate aerogels, the xerogels present significantly higher removal efficiency for both uranium and americium [ 7 ]. Similarly, the nanoparticles show higher relative removal efficiencies, except for pH 9, where the relative removal declines to values below 50%.…”

“…This effect is similar to and has been observed also in laboratory/de-ionized water solutions. Nevertheless, despite the relatively low K d values, both materials present far higher removal efficiency of americium and uranium from seawater than oxidized biochar [ 72 ] or even X-alginate aerogels [ 7 ]. Xerogels could remove both actinide isotopes from seawater by almost 90%, whereas nanoparticles could remove uranium by 80% and americium by 70%.…”