Survey on the valorization of wood and agribusiness wastes for their application as fossil carbon substitutes in metallurgical processes

With the aim of finding new non-fossil carbon sources to decrease the environmental impact of metallurgical processes, this research, conducted as part of the MICS (Made in Italy Circular and Sustainable) project, explores on a laboratory scale the production of biochar from four woody matrices, wood chips, wood pallets, wood pellets, and olive pomace. The biomasses were characterized before and after pyrolysis (process temperature 350 °C and 750 °C) by proximate analysis, activation energy, chemical and mineralogical composition, and the properties compared with those of fossil carbon sources currently used in the metallurgical industry (e.g., coke and graphite). The results represent a starting point for the definitive introduction of upgraded wood waste into metallurgical processes. Specifically, wood pellets pyrolyzed at 750 °C possessed the closest properties to graphite and metallurgical coke (total carbon: 93.51 wt.%, fixed carbon: 83.14 wt.%). Although more volatile matter was observed in the other pyrolyzed matrices (wood chips and olive pomace), the amount of total carbon and the presence of both graphite and/or amorphous carbon allow us to consider them still acceptable for their exploitation as reducing agents for the recovery of valuable metals by pyrometallurgical processes. Finally, since the amount of S in each biochar is far less than that of commonly used metallurgical coke (3.10 wt.%), it is already conceivable that the recovered iron will be free of metallurgical pollutants, thus providing an additional advantage for biochar over fossil carbon sources.