Simultaneous Cr(VI) reduction and non-ionic surfactant oxidation by peroxymonosulphate and iron powder

Some industrial wastewaters contain both hexavalent chromium and surfactants. In this work, their removal from aqueous solution by zero-valent iron (ZVI) and peroxymonosulphate (PMS) was studied using Brij 35 as a representative non-ionic surfactant. The performance of the ZVI/PMS system in the simultaneous removal of both pollutants was compared to that achieved with control solutions containing either Cr(VI) or Brij 35 separately. Reactions were carried out over 24 h at initial pH = 2.3 with variable initial amounts of Cr(VI) and Brij 35. The results showed that surfactant removal was enhanced in the system also containing Cr(VI). Surfactant degradation followed zero-order kinetics and produced formic acid as the main by-product, together with hydroxylated aldehydes, formates and alcohols that were identified by LC/MS. The presence of surfactant similarly enhanced Cr(VI) reduction, which also followed zero-order kinetics. Chromium removal was quantitative only when the initial chromium concentration was lower than 140 mg L−1. Reduced chromium was mainly in the solution phase together with dissolved iron. Precipitation with NaOH was therefore required to definitively remove dissolved metals from the investigated system.

► The redox system zero-valent iron/peroxymonosulfate (ZVI/PMS) was used for the first time. ► Reduction of Cr(VI) and oxidation of a non-ionic surfactant were simultaneously induced. ► Hexavalent chromium and surfactant were quantitatively removed from aqueous solution. ► The effectiveness of ZVI/PMS decreased if either Cr(VI) or surfactant solutions were treated separately. ► By-products of surfactant oxidation were identified.