Synergistic activation of persulfate by manganese sulfide and Fe2+: Roles of Fe and enhancement mechanisms

Manganese sulfide (MnS) has been considered as a persulfate (PS) activator due to the presence of manganese and sulfur elements. Manganese sulfide (MnS) has been considered as a persulfate (PS) activator due to the presence of manganese and sulfur elements. However, the water solubility and hydrophobicity of MnS result in inefficient PS activation. Herein, we demonstrated that the MnS/PS system was significantly efficient for the degradation of phenol in the presence of Fe2+. Within the MnS/PS system, the Fe2+/Fe3+ cycle could act as a station to facilitate the transfer of electrons from Mn2+ and S2- to PS, thereby enhancing electron transfer efficiency. As a result, the degradation efficiency of phenol reached 91.38% within 30 min in the Fe2+/ MnS/PS system, but the MnS/PS system without Fe2+ was only 61.63%, and the reaction rate of the former was 2.52 times that of the latter. In addition, the effects of different conditions on phenol degradation were investigated, including MnS, Fe2+, PS, phenol, initial solution pH, inorganic anions. Quenching experiment and electron paramagnetic resonance (EPR) confirmed that sulfate radical, hydroxyl radical and singlet oxygen were the main active substances in the degradation of phenol. This study provides a promising idea for application in the advanced treatment of groundwater and wastewater at the end of flocculation treatment with high background iron ions.