Fast Debromination of Decabromodiphenyl Ether by Low-Cost Ball Milled Pyrite: Kinetics, Mechanisms, and Pathways

Abstract

The large-scale remediation of polybrominated diphenyl ethers (PBDEs) is often limited by the high manufacturing costs of conventional reductants. We developed a cost-effective method to synthesize submicron pyrite (FeS₂^bm) through simple ball milling of inexpensive pyrite. The mass-normalized removal rate constant of FeS₂^bm for BDE-209 reached 1.6 mg min^–1 g^–1, surpassing previously reported reductants. Ball milling reduced the particle size to 13% of pristine pyrite and increased the specific surface area by 17-fold while removing the oxide layer without altering the crystal structure. The electron transfer capacity of pyrite improved, and kinetic studies showed a positive correlation between the rate constants for BDE-209 removal and milling time, with strong correlations (R² > 0.97) observed among rate constant, pH, debromination rate, and iron-dissolution rate. Mechanistic investigations indicated that degradation occurred primarily via adsorbed Fe(II) and dissolved Fe²⁺. Analysis of degradation products indicated a maximum debromination depth of hexa-BDEs, with predominant products distributed in the hepta-BDE to octa-BDE range, possibly exhibiting higher toxicity. Comparative cost analysis showed that the manufacturing cost of FeS₂^bm is only 1/303 of that of nanoscale zerovalent iron (nZVI). High removal efficiencies of BDE-209 by FeS₂^bm were achieved in groundwater matrices. Consequently, FeS₂^bm emerges as a promising reductant for the cost-effective degradation of BDE-209, showcasing significant potential for practical applications.