Influence of Silicates on the Stability and Reduction of Ferrous Sulfide in Water

In natural water environments, ferrous sulfide (FeS) is often influenced by silicates, the most abundant group of minerals in Earth's crust. The mechanism by which silicates affect pollutant removal by FeS, however, remains unclear. This study shows that silicates alter the surface charge of FeS, increasing electrostatic repulsion between particles, and forming a siloxane film through Fe-O-Si bonding, enhancing spatial resistance. These combined effects significantly improve the stability and antioxidant properties of FeS. In the presence of silicate, the hydrodynamic diameter of FeS is still about 200 nm after 24 h storage. However, silicates inhibit the release of divalent iron ions from FeS, forming complexes that reduce its efficiency in removing Cr(VI). Among the silicates tested, sodium disilicate had the strongest inhibitory effect, reducing removal efficiency by 44 %. Ca2+ and Mg2+ ions form calcium/magnesium silicate precipitates on the FeS surface, disrupting the stabilizing effects of sodium silicate and sodium disilicate, leading to FeS re-stabilization and agglomeration. Additionally, the presence of Ca2+ and Mg2+ reduced the inhibitory effect of these silicates on FeS's ability to remove contaminants. Under this influence, the removal efficiency of Cr(VI) by FeS was improved (5-15 %). Notably, hydrophobic methyl silicates effectively resisted interference from Ca2+ and Mg2+. This study not only reveals the mechanisms by which different silicates interact with FeS but also provides guidance for developing silicate-stabilized ironsulfur-based materials for environmental applications.