Enhanced surface Fenton degradation of BPA in soil with a high pH

Although the heterogeneous Fenton process of iron-bearing minerals has been widely studied due to its potential use for the removal of organic pollutants, the transformation mediated by Fe species in soil particles remains poorly understood. Here, we compared the removal of bisphenol A (BPA) from soil using a Fenton system at low and high pH values. At low pH value, the BPA removal rate decreased with increasing pH value; this result was consistent with the amount of soluble Fe(II) and surface-bound Fe(II) observed in the soil systems. In contrast, an increased BPA degradation efficiency was observed at high pH, which is different from the traditional Fenton system. The electron spin resonance analysis verified that the high BPA degradation rate was attributed to enhanced ·OH generation. The binding environments of the Fe species in the soil for different reaction pH values were investigated by using Mössbauer spectroscopy combined with selective chemical extraction. A mixed-valence Fe(II) phase was observed at pH 12.0 and accounted for 12% of the total Fe content. The results indicate that in addition to the well-studied soluble Fe(II) and surface-bound Fe(II), structural Fe(II) located in the newly formed secondary precipitates may play a more important role in the generation of ·OH, especially at high pH values. These findings may provide insights into the utilization of Fe-bearing soil minerals as a renewable source for the degradation of organic pollutants over a wide pH range.