Battery scrap and biochar utilization for improved metal recoveries in nickel slag cleaning conditions

Abstract

Cobalt is a critical, high-value metal used extensively in batteries and other sustainable technologies. To secure its supply in future, it is utmost important to recover cobalt efficiently from industrial wastes and recycled End-of-Life batteries. This study aims at finding ways to improve the reduction of cobalt as well as valuable metals nickel and copper in nickel slag cleaning furnace conditions by using both traditional fossil-based coke and a more sustainable option, low-CO2 footprint biochar, as reductants. A cobalt-rich fraction of battery scrap (25.5 wt% Co) was also used as a secondary feed. The experimental technique consisted of reduction experiments with different times at 1400◦C under inert atmosphere, quick quenching and Electron Probe X-ray Microanalysis. The use of biochar resulted in faster reaction kinetics in the reduction process, compared to coke. Moreover, the presence of battery scrap had a clear impact on the behavior and reduction kinetics of the elements and/or enhanced settling and separation of matte and slag. The addition of scrap increased notably the distribution coefficients of the valuable metals but consequently also the iron concentration in matte which is the thermodynamic constraint of the slag cleaning process.