A Kinetic Study Investigating the Carbothermic Recovery of Chromium from a Stainless-Steel Slag

In 2018, the stainless-steel industry produced > 10 million tons of slag, which for the most part was landfilled because of chromium oxide contamination. Long-term studies indicate a possible formation of soluble hexavalent chromium, which is classified as carcinogenic. Recent research focuses on the development of a treatment technology to recover chromium from the slag into a ferroalloy, producing an oxidic material that can be utilized in the construction industry. To date, there has been no literature dealing with the kinetics of a carbothermic treatment process to result in a model to predict the necessary treatment time. The present article fills this gap by investigating the reduction kinetics of chromium oxide of a process close to practical applications. Based on experimental measurements, a model has been developed to predict the necessary treatment time to reach a specific final chromium concentration as a function of the starting concentration and required process temperature in the range between 1600 degrees C and 1700 degrees C. Finally, presented findings can serve as a guideline to develop kinetic models in similar pyrometallurgical recovery processes.