Volcanic Ash Leachate as a Low-Cost Catalyst for Fenton-Like Reactions

Abstract

This work deals with the reduction of operating costs of the Fenton-like oxidation of the azo dye Orange II (OII) using volcanic ash leachate as the catalyst. The effect of the volcanic ash concentration and temperature on the total iron concentration of the leachate was studied. Results demonstrated that Fe(II) represented 83 ± 6% of the leachate total iron. Using the obtained leachate as the catalyst for the oxidation of OII, different temperatures (35 to 65 °C), and oxidant feed strategies (batch, pulse feed, or fed-batch) were studied. Hydrogen peroxide (H2O2), total organic carbon concentration (TOC), and UV?Vis spectrum of the reaction mixture were measured as a function of time, while oxidation-reduction potential (ORP)measurements were recorded continuously. Depending on the tested conditions, maximum TOC conversions ranged from 40 to 70%, and H2O2 efficiencies ranged between 3 and 4.6 mgC/mmol H2O2. In addition, ORP measurement allows determining operative conditions that minimize oxidant consumption. Although ORP-based control strategies of fed-batch reactors require more sophisticated equipment in comparison with a batch reactor, they offered more variables to control the process, and therefore, to optimize operating costs.