Separation and recovery of Cr(III) and Cr(VI) using electrodeionization as an efficient approach

Cr(VI) is carcinogenic while Cr(III) is considered to be less toxic. Cr species with combined oxidation states are often found in industrial effluent. It is thus critical to develop techniques that have the capacity for the removal of both Cr(VI) and Cr(III). Here we report, for the first time, the continuous separation and recovery of Cr(III) and Cr(VI) using electrodeionization (EDI) as an advanced and efficient approach. Firstly, we have developed a new analytical method, which integrates UV-Visible spectroscopy and Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), for determining the concentrations of both Cr(VI) and Cr(III) in a mixed solution, and for monitoring the EDI process. Secondly, we have determined the limiting current and systematically studied the effects of different applied currents on the removal of Cr(VI), as well as the recovery of Cr(III) and Cr(VI). Thirdly, the influence of the level of saturation of the ion-exchange resins was assessed in terms of both removal efficiency and energy consumption. It was revealed that the use of fresh ion exchange resins for the EDI process, initially exhibited the very effective removal of both Cr(VI) and Cr(III). Both resins became increasingly saturated subsequent to each cycle, resulting in a gradual lowering of the cell voltage. The continuous and highly efficacious removal of highly toxic Cr(VI) (>99%), and low energy consumption make the EDI process attractive for the separation and recovery of Cr(VI) and Cr(III).