Reduction of perchlorate using zero-valent titanium (ZVT) anode: reaction mechanism

Here we show that perchlorate reduction during pitting corrosion of zero-valent titanium (ZVT) is likely caused by dissolved titanium species, especially Ti(II). Several possible mechanisms were suggested based on the literature and were evaluated based on experimental observations. Direct reduction of perchlorate on the bare metal of the ZVT electrode was thermodynamically infeasible due to the high anodic potential that was applied. Other potential mechanisms were considered such as reduction by small ZVT metal particles released from the electrode and direct reduction on the oxide layer of the electrode where potential was sufficiently reduced by a high ohmic potential drop. However, these mechanisms were not supported by experimental results. The most likely mechanism for perchlorate reduction was that during pitting corrosion, in which ZVT is partially oxidized to form dissolved ions such as Ti(II), which diffuse from the electrode surface and react with perchlorate in solution. This mechanism is supported by measurements of the dissolution valence and the molar ratio of ZVT consumed to perchlorate reduced (∆Ti(0)/∆ClO4 ). The results shown in this study demonstrate that ZVT undergoing pitting corrosion has the capability to chemically reduce perchlorate by producing dissolved Ti(II) and therefore, it has the potential to be applied in treatment systems. On the other hand, the results of this research imply that the application of ZVT undergoing pitting corrosion in treatment systems may not be feasible now due to several factors, including material and electricity costs and possible chloride oxidation.