Degradation of ferrate species produced electrochemically for use in drinking water treatment applications

Stability of ferrate species, produced electrochemically for on-site treatment of drinking water, has been thoroughly studied for a number of important conditions including: pH, temperature, initial concentration effects, and the presence of impurities, in order to assess the degradation process quantitatively. The limited number of ferrate degradation studies reported to this date have all focused on the chemically-produced ferrate species and have examined conditions which are unsuitable for drinking water treatment. Degradation of electrochemical ferrates over a wide temperature range of 5 degrees C to 80 degrees C shows an Arrhenius-type reaction behaviour with an activation energy of 27.3 +/- 0.6kJmol(-1). Initial rate analysis of ferrate degradation reveals a reaction order of about 1. The impacts of potential water impurities, such as salts and natural organic matter, and the source water (e.g. tap, deionized, and natural lake) have been studied and are presented. Degradation of ferrates in the pH range of 5 to 13 appears to have a first-order kinetic behaviour with rate constants ranging from 1.02x10(-3)s(-1) to 6.67x10(-5)s(-1). Understanding the stability properties is important for further development and deployment of on-site generated ferrates for the purposes of drinking water treatment.