Impact of particle size and oxide phase on microplastic transport through iron oxide-coated sand

The presence of microplastics in aquatic environments threatens the ecological system and human health. This study investigates the transport and retention of polystyrene microplastics (PSMPs) in clean sand, and hematite-, goethite-, and magnetite-coated iron oxide - sands as a function of size ratio and ionic strength. The breakthrough curves (BTCs), retention profiles, and hydraulic pressure were measured through soil-column experiments, and the retention of PSMPs was assessed from the observed BTCs, RPs and first-order attachment coefficients. In addition, the maximum attachment capacity was evaluated to assess the long-term retention of PSMPs. Experimental data showed that the retention of PSMPs increased in the order of goethite-, hematite-, and magnetite-coated sands in all size ratios, which is consistent with the order of attraction energy calculated by extended Derjaguin-Landau-Verwey-Overbeek theory. The findings demonstrated the feasibility of mitigating the transport of microplastic particles using naturally abundant iron-rich soils.