One-step electrochemical reduction and precipitation removal of Cr(VI) in acid wastewaters using amidoxime-functionalized carbon felt

Abstract

Traditional electrochemical methods to treat acidic chromium-containing wastewater are often faced with various challenges such as low efficiency, electrode corrosion, and sludge generation. This study proposed a novel method of electrochemical reduction coupled with in-situ precipitation to overcome these drawbacks, and utilized amidoxime-functionalized electrodes to enhance Cr(VI) removal efficiency. The influence of pH and current density and the electrode reusability were also investigated. The results showed that the electrochemical reduction ratio of Cr(VI) on carbon felt cathode increased from 39.5 % to 99.2 % after functionalization with amidoxime groups due to their hydrophilicity and positive electric effect. Concurrently, the generated Cr(III) was hydrolytically precipitated on the cathode even in an acidic bulk solution, resulting in a Cr(T) removal ratio of 87.4 %. Electrochemical H₂O-splitting and O₂ reduction created a local environment of alkaline solution, where Cr(OH)₃ became supersaturated. Increases in both the solution acidity (pH 1.75–3.00) and applied current density (0–12.5 A m⁻²) accelerated the reduction rate of Cr(VI), but first increased and then decreased the cathodic precipitation ratio of Cr(III). The electrodes could be repeatedly reused and regenerated through dissolving the insulated precipitates using diluted hydrochloric acid. This study provides a promising strategy to remove Cr(VI) from acidic wastewaters.