Electrochemical removal of nitrate from the spent regenerant solution of the ion exchange

The electrochemical reduction of nitrate on tin and bismuth was studied under steady-state electrolytic experiments by galvanostatic polarization of the electrodes. The experiments were carried out in a 0.8 M NaHCO3 + 0.015 M NaNO3 medium which represents the resulting solution from the regeneration of the nitrate selective ion exchange resins. The obtained experimental results showed that the yields to nitrogen and nitrous oxide are higher on tin, whereas the rate of the reduction was higher on bismuth. The yield to nitrogen increases as the current density increases on tin while the corresponding yield to ammonia follows the opposite trend. On the contrary, on bismuth, the distribution of the products does not depend strongly on the applied current density. The percentage of Faradaic efficiency (% FE) was similar on both cathodes. The main problems of the process are the low % FE and the high energy cost. Possible ways for the optimization of the process are also included.