Use of Fe and Al Containing Electrocoagulation Sludge as an Adsorbent and a Catalyst in Water Treatment

In this study, three different electrocoagulation (EC) sludges were studied as an adsorbent (removal of humic acids) and as a catalyst [catalytic wet peroxide oxidation (CWPO) of bisphenol A (BPA)]. The sludges originated from electrocoagulation process in which aluminum (Al) and iron (Fe) electrodes were used for the treatment of mining industry wastewater. All the materials were used as dried sludge and calcined material. The stability of these materials was studied in neutral and alkaline conditions with analysis of the leached iron content in solution. Based on the EC sludge characterization with X-ray fluorescence (XRF), X-ray diffractometer (XRD), and diffuse-reflectance infrared Fourier transform (DRIFT) spectroscopy different forms of Fe occurring in EC sludges were found. The Brunauer–Emmett–Teller (BET) method showed reduced surface area after calcination process. Stability of the sludges was studied in neutral conditions, and the amount of iron leaching was low (<1.4 ppm). Adsorption experiments showed that the removal of humic acids (measured as total organic carbon) was over 50% in all tested materials in the pH range of 3–9, and over 92% with the S3 calcined material in all studied pH range. The calcined samples were catalytically more active than raw material in CWPO of BPA. The highest removal of BPA was 85% over calcined sludge. Therefore, calcined EC sludges are suitable materials for catalyst and adsorbent use. The main novelty of this paper was the finding of sludge modification in the EC process of water treatment through different electrode material and current density. This modification can be made in EC water treatment process, and it may provide low-cost materials to different utilization of EC sludge.