In situ stabilization of metal(loid)s-contaminated groundwater by iron sulfide: A reactive and efficient nano-coating

Iron sulfide nanoparticles (Nano-FeS) have shown great potential for in situ remediation of heavy metal and metalloid contamination from groundwater. However, limitations on mass transfer and efficacy of nano-FeS in the subsurface pose significant challenge. Herein, a reactive and efficient nano-FeS coating was developed in situ for the stabilization of metal(loid)s from groundwater. Alternate injection of FeSO 4 and Na 2 S can realize nano-FeS coating on sand grains with negligible changes in porosity, and the formation was dominated by growth and agglomeration process. Application scenarios for this nano-FeS coating include permeable reaction walls designed for preventive measures and in situ reaction zones that have experienced contamination. For the first scenario, the preformed nano-coating effectively sequesters As(III) through surface complexation and precipitation, and sequesters Cr(VI) through surface adsorption and reduction/precipitation. The retardation factor of As(III) and Cr(III) increased by 5.9 and 8.3 times, respectively, relative to the unamended sand. For the second scenario, we used alternate injection of FeSO 4  + heavy metal (Cd, Pb, and Cu) and Na 2 S to simulate the in situ immobilization of contaminants from real groundwater. The results showed that the alternating injection of Fe 2+ and HS − significantly enhanced the immobilization of heavy metals through both adsorption and direct interaction between heavy metals and HS − , with minimal detachment from the quartz sands. Overall, the findings highlight that in situ formation of nano-FeS coating as aquifer materials has significant potential as a cost-effective and straightforward groundwater remediation technology under environmentally relevant conditions.