Electrochemical cobalt extraction from grinding sludge for supercapacitor applications via hydro- and solvometallurgical processes

Cobalt is a critical material for energy storage applications, including supercapacitors, but its supply is constrained by geopolitical and environmental challenges. This study presents a sustainable approach for cobalt recovery from cemented tungsten carbide grinding sludge via deep eutectic solvents (DESs) and evaluates the electrochemical performance of the recovered materials in supercapacitors. Electrochemical extraction was optimized at 4 V and 10 mA/cm 2 , achieving a cobalt concentration of 2900 mg/L in the DES. The cobalt was then recovered as cobalt oxalate via solvometallurgical (Route 1) and hydrometallurgical (Route 2) processes and subsequently calcined into cobalt oxide. Characterization revealed that the solvometallurgical route yielded finer, porous particles with enhanced electrochemical properties. The recovered cobalt oxalate and cobalt oxide were utilized in supercapacitor electrodes, demonstrating superior electrochemical performance when combined with activated carbon (AC). Supercapacitors incorporating cobalt oxide from route 1 with AC achieved a specific capacitance of 95 F/g, outperforming cobalt oxalate-based electrodes (89 F/g) at 1 mA/g. The AC-modified electrodes exhibited improved energy and power densities, with stable capacitance retention over 1000 cycles. Comparative analysis with direct deposition methods highlighted the multistep recovery process as a promising route for scalable cobalt recycling. This study underscores the potential of DES-based electrochemical extraction as an environmentally friendly alternative for critical metal recovery, aligning with circular economy principles and sustainable energy storage solutions. • Sustainable cobalt recycling from cemented carbide sludge using deep eutectic solvents. • The solvometallurgical route yields finer cobalt oxalate with superior electrochemical traits. • The cobalt oxide supercapacitor with AC has a 95 F/g capacitance, outperforming oxalate. • Compared with direct deposition methods, enhanced power density is achieved via a multistep process. • Stable capacitance retention over 1000 cycles promoted circular economy solutions.