Magnetic iron oxide and manganese-doped iron oxide nanoparticles for the collection of alpha-emitting radionuclides from aqueous solutions

Abstract

Magnetic nanoparticles are well known to possess chemically active surfaces and large surface areas that can be employed to extract a range of ions from aqueous solutions. Additionally, their superparamagnetic properties provide a convenient means for bulk collection of the material from solution after the targeted ions have been adsorbed. Herein, two nanoscale amphoteric metal oxides, each possessing useful magnetic attributes, were evaluated for their ability to collect trace levels of a chemically diverse range of alpha emitting radioactive isotopes (polonium (Po), radium (Ra), uranium (U), and americium (Am)) from a wide range of aqueous solutions. The nanomaterials include commercially available magnetite (Fe3O4) and magnetite modified to incorporate manganese (Mn) into the crystal structure. The chemical stability of these nanomaterials was evaluated in Hanford Site, WA ground water between the natural pH (~8) and pH 1. Whereas the magnetite was observed to have good stability over the pH range, the Mn-doped material was observed to leach Mn at low pH. The materials were evaluated in parallel to characterize their uptake performance of the alpha-emitting radionuclide spikes from ground water across a range of pH (from ~8 down to 2). In addition, radiotracer uptake experiments were performed on Columbia River water, seawater, and human urine at their natural pH and at pH 2. Despite the observed leaching of Mn from the Mn-doped nanomaterial in the lower pH range, it exhibited generally superior analyte extraction performance compared to the magnetite, and analyte uptake was observed across a broader pH range. We show that the uptake behavior of the various radiotracers on these two materials at different pH levels can generally be explained by the amphoteric nature of the nanoparticle surfaces. Finally, the rate of sorption of the radiotracers on the two materials in unacidified ground water was evaluated. The uptake curves generally indicate that equilibrium is obtained within a few minutes, which is attributed to the high surface areas of the nanomaterials and the high level of dispersion in the liquids. Overall, the results indicate that these nanomaterials may have the potential to be employed for a range of applications to extract radionuclides from aqueous solutions.

Magnetic iron oxide nanoparticles for the collection and direct measurement of adsorbed alpha-emitting radionuclides from environmental waters by liquid scintillation analysis

“…Chemical properties such as pH, conductivity, and alkalinity were previously reported for the two water samples. 40…”

“…Analyte capture mechanisms on the Fe 3 O 4 surface include simple adsorption on the charged polar surface, ion exchange, and redox reactions. 37–40 There have been a number of studies showing the efficacy of the metal hydroxyl surface as a sorbent for heavy metal 41,42 and radioactive analyte species. 40,43,44 Additionally, Feraheme®, a magnetite nanomaterial coated with polyglucose sorbitol carboxymethylether, has been used as a carrier for the diagnostic radionuclides 64 Cu, 89 Zr, and 111 In for in vivo imaging applications ( e.g.…”

“…47–54 Iron oxide nanoparticles (NPs) composed of these or similar mineral phases have been shown to have significant chemical affinity toward the relevant species in even the most complex sample matrixes such as sea water and urine. 40,44…”

“…The use of magnetic nanoparticles (MNPs) to capture a range of radionuclides from naturally occurring water matrices was recently presented by the authors. 40 The study demonstrated that naturally occurring and man-made α-emitting radionuclides (Po, Ra, U, and Am) could be sorbed onto MNPs in river, ground, and sea water, as well as human urine, across a range of pH. In addition to Fe 3 O 4 NPs, the authors evaluated Mn-doped Fe 3 O 4 , which exhibited enhanced analyte extraction properties for these radionuclides while maintaining the useful magnetic attributes.…”

“…While it has been previously demonstrated that 210 Po has virtually quantitative uptake on Fe 3 O 4 NPs between pH ~ 1–8 solutions, 241 Am affinity begins to drop below pH ~ 5. 40 Therefore, the method demonstration was performed with unaltered river water pH for 241 Am, while the 210 Po demonstration was performed at both pH 2 and ~8 in ground water. The resulting analyte-sorbed MNPs are then used to form a suspension in the liquid scintillation cocktail so as to demonstrate LS analyzer performance and limitations.…”