Abstract
Nanoparticulate iron sulfides (nano-FeS) with high reactivity have shown tremendous potential as an effective environmentally friendly material for in situ soil and groundwater remediation. However, bare nano-FeS are susceptible to aggregation and oxidation aging, which limits their reactivity and engineering application because of limited mass transfer and formation of the passivation layer. Herein, nano-FeS were modified by surface functionalization using sodium hyaluronate (SoH), and the effect of modification on colloidal stability, sedimentation, oxidation resistance, mobility, and reactivity with Cr(VI) was investigated. The results demonstrated that SoH could stabilize FeS (SoH-FeS) using SoH-to-FeS molar ratios of ≥0.001, with the stabilizer effectively soldered onto the surfaces as bidentate bridging through the carboxylic group, providing electrostatic and steric repulsion that prevented particle aggregation. Compared with bare FeS, the sedimentation rates of modified FeS decreased and oxidation resistance and transport increased significantly. The improved transport performance of SoH-FeS was further achieved by decreasing the injection mass concentration and increasing the flow rate. SoH-FeS increased the Cr(VI) sequestration efficiency from 57.5% to 99.9% relative to pristine FeS, and the removal processes followed the pseudo-second-order kinetic model (R2 ≥ 0.998). The coexistence of reaction products (i.e., α-FeOOH, polysulfide, and Cr(OH)3) revealed by X-ray diffraction and X-ray photoelectron spectroscopy analysis with different Cr speciation concentrations in the aqueous phase suggested surface sorption (26.8%) and reduction/precipitation (73.2%) were the dominant removal mechanisms. Higher pH and humic acid concentrations modestly inhibited Cr(VI) removal efficiency. The results demonstrate an efficient method for enhancing nano-FeS mobility and reactivity for in situ remediation of contaminated soils and groundwater.
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