Sulfur-Impregnated Nanoscale Fe ⁰ via Ball Milling and Desulfurization of Commercial Microscale Pyrite for Groundwater Remediation

Sulfidized nanoscale zerovalent iron (SNZVI) has shown great potential in groundwater remediation. However, the high production cost of bottom-up synthesizing of SNZVI with borohydride limits its scalability and applicability. Here, SNZVI with a controllable structure and good performance was successfully synthesized from commercial and brittle microscale pyrite through ball milling and desulfurization. SNZVI_pyrite particles with evenly impregnated S possessed a nanosized morphology (median particle size 290 ± 58 nm). The addition of Fe³⁺ during the synthesis facilitated efficient pyrite decomposition through redox reactions, thereby. This process showed a linear correlation with the resulting Fe⁰ and S contents and achieved a conversion of over 95% of pyrite to Fe⁰. These tunable structures and physicochemical properties characterized at particle, crystal, and atomic levels well explained the materials' performance. The dechlorination reactivity and selectivity of SNZVI_pyrite were 4.1-11.6 and 3.2-28.7 times higher than those of NZVI, respectively, comparable to borohydride-reduced SNZVI. The scalability (up to 1 kg) and production cost of SNZVI_pyrite were assessed via batch synthesis and techno-economic analysis, which could be 11.5-fold cheaper than borohydride-reduced SNZVI. These results indicate a scalable top-down synthesis approach of SNZVI via ball milling and desulfurizing cheap microscale pyrite for efficient and selective dechlorination, making this emerged groundwater remediation agent promising toward real applications.