Kinetic studies of the electrochemical treatment of nitrate and nitrite ions on iridium-modified carbon fiber

Electrochemical reductions of nitrate and nitrite ions in neutral solution were studied using an Ir-deposited carbon fiber electrode. The objective of the study was to set up a process to remove nitrate and nitrite ions from industrial and municipal wastes as well as from the nitrate and nitrite ion enriched water supplies. Since nitrate and nitrite ion reduction kinetics is very slow on plain carbon, the iridium-modified fibers showed a significant reduction of nitrate and nitrite ions. Nitrogen and ammonia were identified as the two major gaseous products of the reduction process. A first-order inhibition kinetics model is proposed and was used to analyze the nitrate and nitrite ion reduction kinetics. The reduction rates of nitrate and nitrite ions were favored at higher cathode potential (cf. -950 mV and -850 mV) in a solution of pH = 7.0 with hydrogen evolution efficiency increasing with cathodic potential. A simple model for the batch re-circulation process was developed for the reduction of nitrate ion at surface-modified fiber electrode. There was a good agreement between the model predictions and experimental results.