Synergistic Interaction between Electricigens and Natural Pyrrhotite to Produce Active Oxygen Radicals

Abstract

In this work we demonstrated that the active oxygen radicals could be produced by the synergistic interaction between electricigens and natural pyrrhotite. The identification of such an interactive pathway was conducted by using a fuel cell-type design, in which the electricigen-attached carbon felt electrode was used as the anode and the pyrrhotite-coated graphite electrode was used as the corresponding cathode. Current density, polarization and power density curves obtained at different treatments demonstrated the synergistic effects of electricigens and pyrrhotite improved the electrons transfer rate between them. Cyclic voltammetry (CV) analysis showed the reductive peaks of O₂/H₂O₂ at 0.88 V (vs. SCE, saturated calomel electrode) and ionic and structural Fe(III)/Fe(II) at 0.31 V (vs. SCE) and 0 V (vs. SCE), respectively. The electrochemical results indicated the electricigen-assisted pyrrhotite photoelectrochemical reactions gave rise to Fenton's reagents: Fe²⁺ and H₂O₂, which underwent a further reaction to generate active oxygen radical ·OH. By using N, N-dimethyl-p-nitrosoaniline discoloration as a model reaction, the ·OH production rate at the pyrrhotite-cathode was found to follow the first-order kinetics. Practical application of the synergistic interaction between the electricigen and natural pyrrhotite to a real old-aged landfill leachate degradation resulted in 78% chemical oxygen demand (COD) removal and 77% decolourization efficiency. The current generation lasted more than 45 days verified the validity of such system in long-term operation. The proposed interactive pathway would be expected as an alternative cost-effective technology for future wastewater treatment.

Keywords:

• pyrrhotite
• electricigen
• fuel cell
• synergistic interaction
• electrochemical
• Fenton

Acknowledgments

This work was supported by the National Basic Research Program of China (973 Program, Program No. 2007CB815602), the Special Project Funding of Beijing Municipal Education Commission and the National Program of Control and Treatment of Water Pollution (2009ZX07424-002). We’d like to thank Beijing Synchrotron Radiation Facility for giving us the beam time for the XANES measurement.