A Crucial Step Toward Carbon Neutrality in Pyrometallurgical Reduction of Nickel Slag

This study aims at recovering valuable metals from nickel slag by employing pyrometallurgical techniques. A large amount of slag is generated during the nickel matte smelting. Nickel slag contains valuable elements such as copper, nickel, and cobalt, which can be recovered. Disposal of this slag results in loss of resources and may cause pollution of the environment. It is important to retrieve these metals for environmental and economic reasons. In this study, the slag was reacted with non-fossil reducing agents (biochar) which were produced from hydrolysis lignin and black pellet biomass by pyrolysis at 600 and 1200 °C, and with metallurgical coke for comparison. The reduction experiments were done at 1400 °C for 15, 30, and 60 min under inert gas atmosphere. The samples were quickly quenched and analyzed with Electron Probe X-ray Microanalysis. The results showed that the use of biochar resulted in faster reaction kinetics in the reduction process compared to coke. Moreover, thermodynamic modeling was also performed using Factsage to simulate equilibria with different amounts of biochar. The metal-to-slag distribution coefficient calculated from the results of thermodynamic modeling was consistent with experimental results. Graphical Abstract: [Figure not available: see fulltext.].