Speaker
Description
Aging and fragmentation processes of plastic debris favor the formation of reactive micro- and nano-plastic (NPs) particles, which behave as vectors of pollutants in porous media. One of the most common types of NPs is made of polystyrene polymer (PS) that has shown selective adsorption towards metals, e.g., lead (Pb$^{2+}$) and arsenic, under typical fresh-water and shallow aquifer conditions.
In this presentation, we will report the results from an experimental and modeling study where NP-facilitated transport of Pb$^{2+}$ through reactive porous media has been investigated. A system made of PS-NPs, Pb$^{2+}$, and sand was studied at ambient temperature and between $p$H 4 and 6.
A chromatographic column containing quartz sand and hydrous manganese oxide (HMO) coated sand was flooded with solutions and suspensions of known composition, and the effluent was continuously monitored inline with a $p$H probe, ion chromatography, and UV-Vis spectrophotometry.
A reactive transport model coupling conservation laws with geochemistry was developed to describe the measurements and gain insight into the dominant mechanism governing the transport.
Preliminary results show that regardless of the porous medium, $\mathrm{Pb}^{2+}$ and PS show increasing retardation and retention with increasing $p$H, respectively, due to $p$H-dependent surface interactions. Moreover, $\mathrm{Pb}^{2+}$ partitioning shifts toward PS-NP surfaces with increasing pH, resulting in reduced $\mathrm{Pb}^{2+}$ retardation and enhanced co-mobilization of the metal with NPS.
Breakthrough curves, well captured by the model, indicate that $\mathrm{Pb}^{2+}$ increasingly follow PS transport as pH approaches neutrality (pH 5.5-6), consistent with competitive desorption from sand and adsorption onto negatively charged PS surfaces.
Overall, the experimental and modeling results demonstrate that PS-NPs can act as carriers for $\mathrm{Pb}^{2+}$ in porous media, with negative implications for metal fate and transport in contaminated soils and aquifers.
| Country | Italy |
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