Effects of common groundwater ions on the transformation and reactivity of sulfidized nanoscale zerovalent iron

Sulfidized nanoscale zerovalent iron (S-nZVI) is an Fe-based reactant widely studied for its potential use for groundwater remediation. S-nZVI reactivity has been widely investigated testing various contaminants in various water matrices, but studies on S-nZVI corrosion behaviour and reactivity upon exposure to complex groundwater chemistries are limited. Here, we show that anoxic aging of S-nZVI for 7 days in the absence and presence of key groundwater solutes (i.e., Cl⁻, SO₄²⁻, Mg²⁺, Ca²⁺, HCO₃⁻, CO₃²⁻, NO₃⁻, or HPO₄²⁻) impacts Fe⁰ corrosion extent, corrosion product and reduction rates with trichloroethene (TCE). White rust was the dominant corrosion product in ultrapure water and in SO₄²⁻, Cl⁻, Mg²⁺ or Ca²⁺ solutions; green rust and/or chukanovite formed in HCO₃⁻ and CO₃²⁻ solutions; magnetite, formed in NO₃⁻ solutions and vivianite in HPO₄²⁻ solutions. The aged S-nZVI materials expectedly showed lower reactivities with TCE compared to unaged S-nZVI, with reaction rates mainly controlled by ion concentration, Fe⁰ corrosion extent, type(s) of corrosion product, and solution pH. Comparison of these results to observations in two types of groundwaters, one from a carbonate-rich aquifer and one from a marine intruded aquifer, showed that S-nZVI corrosion products are likely controlled by the dominant GW solutes, while reactivity with TCE is generally lower than expected, due to the multitude of ion effects. Overall, these results highlight that S-nZVI corrosion behaviour in GW can be manifold, with varied impact on its reactivity. Thus, testing of S-nZVI stability and reactivity under expected field conditions is key to understand its longevity in remediation applications.