Impact of dissolved silica on arsenite removal by nano-particulate FeS and FeS-coated sand

► Arsenite retention by the FeS was not significantly affected by dissolved silica. ► Arsenic-sulfur solid phase associations implicated in lack of dissolved silica impact. ► FeS-based sorbents may have advantage over Fe oxyhydroxides for arsenite retention. This work evaluated the inhibitory effect of dissolved silica on arsenite adsorption to nanoparticulate FeS (NP-FeS) or mackinawite and FeS-coated sand (CS-FeS) sorbents. Arsenite retention by the NP-FeS solid was not affected by dissolved silicate over a wide range in pH, in contrast to the known inhibitory effect of dissolved silica on As(III) uptake by Fe-(hydr)oxide systems. However, some inhibition was observed in CS-FeS system at pH 9. This latter result is attributed to the co-existence of both FeS and small amounts of Fe-(hydr)oxide phases on the sand surface. Given the ubiquitous presence of dissolved Si in groundwater, FeS-based sorbents may have an advantage for As retention compared to those based on Fe-(hydr)oxides in reducing subsurface environments.