Session: Applications & Implications of Nanomaterials in the Environment:

Lead contamination in soils poses a hazard to human health. Phosphate is commonly used to immobilize lead due to the formation of lead phosphate particles with low solubility. However, the effectiveness of this lead remediation strategy can be diminished if particle transport occurs. This study investigated the effects of various aqueous parameters on deposition behaviors of lead phosphate particles in porous media by conducting column experiments. Derjaguin–Landau–Verwey–Overbeek (DLVO) theory was employed to estimate interaction energies and predict the particle deposition behavior in clean bed filtration models (accounting for only particle-clean sand collector interactions). While clean bed filtration theory was applicable at low ionic strength, it failed to predict the transport of particulate lead across a range of possible porewater chemistries. Notably, for both fresh and aged (24 hrs) suspensions, ripening occurred at high ionic strength (e.g., 12.5-20 mM NaNO₃). Furthermore, straining took place in addition to ripening for aged suspensions that were highly aggregated. The observed phenomena were consistent with homoaggregation results showing the increasing significance of particle-particle attachment at these ionic strengths. Hence, the results suggest that homoaggregation experiments can potentially provide the necessary data to predict when ripening and straining become important and to parameterize such models. In the presence of Ca²⁺(0.2 and 1 mM), particles were much less negatively charged, leading to enhanced aggregation and deposition; however, natural organic matter (NOM) was found to suppress the deposition of lead phosphate particles via steric repulsion. Given the observed importance of NOM on the particle stability, further investigation of the influence of different types of NOM on the particle aggregation will be discussed. In summary, this study reveals controlling mechanisms of deposition behaviors of lead phosphate particles under several conditions relevant to soil environments and provides useful information to predict transport of lead phosphate particles in soils.

Daniel Giammar

Washington University

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