Electrosorption-Driven Nickel Recovery from Real Industrial Effluents Using Capacitive Deionization

The electro-driven recovery of heavy metal from industrial wastewater is a more promising way to achieve sustainable water treatment and resource valorization. In the present study, the feasibility of selective removal and recovery of Ni²+ from aqueous streams is investigated for the use of a redox-active hybrid electrode system in capacitive deionization (CDI) process. The electrode structure is optimized for promoting high charge transfer rate and high ion accessibility to achieve better electrosorption performance. The system showed a high adsorption capacity of ~75.6 mg g⁻¹ with rapid adsorption under optimum conditions (applied potential: 1.4 V, pH: 6, flow rate: 10 mL min⁻¹) and kinetic analysis showed excellent agreement with the pseudo-second order model (R² ≈ 0.998), which indicates that an electrochemical adsorption mechanism dominated by the surface-controlled mechanism is the predominant process. The initial adsorption rate was high which indicates the good interaction with the active sites and the Ni²⁺ ions. The mass transfer evaluation showed a multi-stage model with external film diffusion, intraparticle diffusion and lastly electrosorption into the porous matrix. The electrochemical stability of the CDI system was outstanding, with a coulombic efficiency greater than 99.99%, and a capacity retention over 95% following multiple adsorption–desorption cycles. The specific energy consumption in the energy analysis was found to be ~2.2 kWh m⁻³, with an estimated treatment cost of ~1.32 $ m⁻³, which proved the treatment to be practical. In contrast to conventional carbon based CDI systems, the performance of which is usually 20–40 mg g-1 for divalent ions, the present system exhibits much enhanced performance. Importantly, the process allows for efficient Ni²⁺ recovery with a chemical free regeneration process, reducing secondary waste generation. Based on all of the above it could be concluded that CDI is a potential, promising, energy efficient and scalable technology for selective removal of heavy metals and recovery of resources from real industrial wastewater systems.