Investigation of the behaviour of zero-valent iron nanoparticles and their interactions with Cd2+ in wastewater by single particle ICP-MS

Zero-valent iron nanoparticles (nZVI) exhibit great potential for the removal of metal contaminants fromwastewater. After their use, there is a risk that nZVIwill remain dispersed in remediatedwater and represent potential nano-threats to the environment. Therefore, the behaviour of nZVI after remediation must be explored. To accomplish this, we optimised a novel method using single particle inductively coupled plasmamass spectrometry (SP-ICP-MS) for the sizing and quantification of nZVI inwastewater matrices. H2 reaction gaswas used inMS/MS mode for the sensitive and interference-free determination of low concentrations of nZVI with a lowsize limit of detection (36 nm). This method was applied to study the influence of different iron (Fe) loads (0.1, 0.25, 0.5 and 1.0 g L-1) and watermatrices (Milli-Q water, synthetic and effluent wastewater) on the behaviour of nZVI, their interactionswith Cd2+ and the efficiency of Cd2+ removal. The aggregation and sedimentation of nZVI increased with settling time. Sedimentation was slower in effluent wastewater than in Milli-Qwater or syntheticwastewater. Consequently, Cd2+ was more efficiently (86%) removed from effluent wastewater than from synthetic wastewater (73%), while its removal from Milli-Q water was inefficient (19%). The trace amounts of Cd2+ that remained in the remediated water were either dissolved or sorbed to residual nZVI. The results of the nanoremediation of effluent wastewater with varying Fe loads showed that sedimentation was faster at higher initial concentrations of nZVI. After seven days of settling, low concentrations of Fe remained in the effluent wastewater at Fe loads of 0.5 g L-1 or higher, which could indicate that the use of nZVI in nanoremediation under the described conditions may not represent an environmental nano-threat. However, further studies are needed to assess the ecotoxicological impact of Fe-related NPs used for the nanoremediation of wastewaters. (C) 2018 Elsevier B.V. All rights reserved.