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

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 NaCrO from EPS using an integrated bipolar membrane electrodialysis (BMED)-HO oxidation technology. During the treatment process, Cr(III) was oxidised to Cr(VI) using HO in an alkaline environment, BMED was used to separate and recover Cr(VI). Experimental results showed that HO dosage and pH affected Cr(III) oxidation-the highest Cr(III) oxidation ratio of 68.4% was observed when HO 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/cm, 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 NaCrO 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.