Field Application of Iron and Iron–Nickel Nanoparticles for the Ex Situ Remediation of a Uranium-Bearing Mine Water Effluent

In this work, sodium borohydride reduced nanoscale zero-valent iron (nZVI–BR), sodium borohydride reduced nanoscale zero-valent iron–nickel (nZVIN–BR), nanoscale zero-valent iron sourced from NanoIron, s.r.o. (nZVI–Star), and nanoscale zero-valent iron sourced from Toda Kogyo Corporation (nZVI–RNIP) have been tested for the ex situ removal of aqueous uranium (U) from a bicarbonate-rich mine water effluent. Laboratory scale (2 L) batch treatment systems containing the mine water and comparator uranyl solutions were tested to compare U removal efficacy and aqueous corrosion behavior of the different nanopowders. The two commercially sourced nanopowders were also tested for the removal of U from 2,500 L batch systems to determine the nature of any differential behavior exhibited by the nanopowders when deployed at commercial scale. Analysis of aqueous samples taken at periodic intervals throughout the 96 h reaction period using inductively coupled plasma mass spectroscopy recorded >95%>95% aqueous U removal within 15 min by the sodium borohydride reduced nanopowders in all systems studied. Similar behavior was exhibited by the commercially sourced nanopowders for the uranyl-only solutions; however, a maximum of only 30.0 and 43.2% removal was recorded for the 2 L mine water effluent by nZVI–Star and nZVI–RNIP, respectively. Similar U uptake behavior was exhibited by the commercially sourced nanopowders for the 2,500 L batch treatment systems; however, a redox and U removal gradient as a function of depth was recorded, compared to a homogenous distribution recorded for the 2 L experiments. Analysis of reacted nanoparticulate solids using X-ray diffraction determined only minor aqueous corrosion of the two commercial nanopowders whereas near-total conversion to iron (hydr)oxides was recorded for the sodium borohydride reduced nanopowders. Results therefore demonstrate that in order for effective U removal from waters containing appreciable concentrations of complexing agents, highly reactive forms of iron and iron–nickel nanoparticles are required. In addition, the performance of such materials in commercial scale applications is likely to be lower than in laboratory-scale experiments due to the significant technical challenge of homogenous mixing/dispersion of the nanopowder with the aqueous phase.