Activation of Persulfates Using Siderite as a Source of Ferrous Ions: Sulfate Radical Production, Stoichiometric Efficiency, and Implications

Ferrous ions (Fe2+) rapidly activate persulfates to produce sulfate radicals. However, the high reactivity of Fe2+ toward sulfate radicals means that they are easily scavenged, which reduces the stoichiometric efficiency of persulfates. To improve the stoichiometric efficiency, siderite was used to activate peroxydisulfate (PDS) and peroxymonosulfate (PMS), with phenol as a model contaminant. Near-100% degradation of phenol was achieved by siderite-activated PDS or PMS. In contrast, only 34% and 25% of the phenol was degraded by Fe2+- and nanoscale-magnetite-activated persulfates, respectively. The stoichiometric efficiencies of PMS and PDS activated by siderite were more than 4.4 and 3.6 times higher, respectively, than those activated by Fe2+. Electron paramagnetic resonance recorded both sulfate radicals and hydroxyl radicals. The effects of pH, iron dissolution, and scavenging were characterized, and the results indicated that siderite mainly activated persulfates by acting as a source of Fe2+ and that sulfate radicals were the major active species. The release of Fe2+ and the production of sulfate radicals were controllable via the pH of the solution. No deactivation occurred when the siderite was reused, because the acidic environment partially dissolved the surface. These findings may facilitate the application of iron bearing materials for sulfate radical production.