Photocatalytic removal of cyanide and Cr(IV) from wastewater in the presence of each other by using TiO2/UV

Cyanide (CN) and chromium (VI) are hazardous, toxic pollutants whose presence in water and wastewater can seriously affect human and its environment, hence the necessity of controlling these contaminants. In this work, by using TiO2/UV, the simultaneous photocatalytic reduction of Cr(VI) and oxidation of CN in aqueous suspensions were investigated. Variations of this study were pH, pollutant concentration, and reaction time. CN and total chromium were determined by Titrimetric method, and Colourimetric method, respectively. Maximum removal of chromium and CN occurs at pH 2.3 and 10, respectively. In the binary system, the electron-hole recombination is blocked and as a result, total efficiency increases. An increase in the initial concentrations of CN and Cr(VI) led to a rise in the reduction efficiency of Cr(VI) and CN up to an optimum amount, and then it went into decline as the concentration of the pollutants increased any further. The maximum quantum efficiency of Cr(VI) photoreduction with CN being present was calculated to be 23% at room temperature. Furthermore, the kinetic experimental was investigated and it became evident that the pseudo-first-order kinetic model is capable of defining Cr(VI) and CN both. Finally, based on the obtained results, a TiO2 system is proposed to remove both pollutants.