Simultaneous recovery of vanadium and nickel from power plant fly-ash: Optimization of parameters using response surface methodology

•Leaching of vanadium and nickel from fly ash (14.43% V and 5.19% Ni) in sulfuric acid was performed.•Optimization of leaching parameters was carried out using a response surface methodology.•Using optimum conditions, 94.28% V and 81.01% Ni “actual recovery” was obtained. Simultaneous recovery of vanadium (V) and nickel (Ni), which are classified as two of the most hazardous metal species from power plant heavy fuel fly-ash, was studied using a hydrometallurgical process consisting of acid leaching using sulfuric acid. Leaching parameters were investigated and optimized in order to maximize the recovery of both vanadium and nickel. The independent leaching parameters investigated were liquid to solid ratio (S/L) (5–12.5wt.%), temperature (45–80°C), sulfuric acid concentration (5–25v/v%) and leaching time (1–5h). Response surface methodology (RSM) was used to optimize the process parameters. The most effective parameter on the recovery of both elements was found to be temperature and the least effective was time for V and acid concentration for Ni. Based on the results, optimum condition for metals recovery (actual recovery of ca.94% for V and 81% for Ni) was determined to be solid to liquid ratio of 9.15wt.%, temperature of 80°C, sulfuric acid concentration of 19.47v/v% and leaching time of 2h. The maximum V and Ni predicted recovery of 91.34% and 80.26% was achieved.