Recovering chromium from electroplating sludge using an integrated technology of bipolar membrane electrodialysis and H₂O₂ oxidation.

Abstract

Chromium electroplating produces Cr(III)-containing electroplating sludge (EPS) in large volumes, which is easily oxidised to Cr(Ⅵ) and is harmful to the environment and human health. This study recovered Cr(III) as Na₂CrO₄ from EPS using an integrated bipolar membrane electrodialysis (BMED)-H₂O₂ oxidation technology. During the treatment process, Cr(III) was oxidised to Cr(VI) using H₂O₂ in an alkaline environment, BMED was used to separate and recover Cr(VI). Experimental results showed that H₂O₂ dosage and pH affected Cr(III) oxidation-the highest Cr(III) oxidation ratio of 68.4% was observed when H₂O₂ dosage and pH were 5.5 mL and 12.0, respectively. The current density, solid/liquid ratio and sludge particle size affected Cr(III) recovery, energy consumption and current efficiency. Under a current density of 20.0 mA/cm², solid/liquid ratio of 1.0:45 and sludge particle size of 100 mesh, 58.2% of Cr(III) was recovered. When the number of the equipped EPS compartments was increased from one to two and three, the specific energy consumption decreased from 1.04 to 0.87 and 0.81 kW h/g, respectively, but the current efficiency remained almost constant. After EPS treatment, the Cr(III) remaining in the sludge was mainly in the residual state, which is less environmentally harmful. The obtained Na₂CrO₄ had similar properties according to X-ray diffraction analysis. Thus, the proposed integrated technology effectively recovers Cr(III) from EPS and other chromium-containing solid wastes.