Hematite as a natural mineral in activating persulfate to degrade chlorinated compounds: combined effects of soluble iron release and surface activation

In this study, six naturally occurring iron-containing minerals (pyrite (FeS₂), magnetite (Fe₃O₄), ilmenite (FeTiO₃), hematite (Fe₂O₃), limonite (FeO(OH)·nH₂O), siderite (FeCO₃)) were examined on activation of persulfate for degradation of 1,1,2-TCA in groundwater. Hematite was selected for further study due to its abundance in subsurface porous media, low persulfate consumption, and efficient 1,1,2-TCA removal. Through ferric ion-activated persulfate experiments and model simulations, we found that hematite activates persulfate through a combination of surface reactions (40%) and dissolved ferric ion activation (60%). High persulfate concentration and lower pH resulted in an increase in the degradation rate. Column experiments revealed a notable improvement in 1,1,2-TCA degradation when natural hematite was employed as the activator. Dissolution-advection-reaction model well described the dissolution process of hematite and degradation process of 1,1,2-TCA in the column. A decrease in efficiency of hematite activation was observed and model simulation showed that this was primarily due to a decrease in ferric ion release. This study underscores the potential of natural hematite minerals in activating persulfate for chlorinated solvent degradation, which should be considered in application of persulfate-based ISCO technologies to reduce cost.