Preparation and Characterization of Mill Scale Industrial Waste Reduced by Biomass-Based Carbon

Utilizing locally based and renewable biomass resources are challenging. This work aims to understand the role of the utilization of solid byproduct of Indonesian mill scale, formed during the cold rolling process, and abundant local resources of coconut coir wastes. Mill scale has a fairly high total iron content with the dominant phase being hematite, while pure Fe content is insignificant. In this study, we utilized coconut coir-based carbon (CCC) for direct reduction of mill scale via a carbothermic process to enhance its metallic Fe content. The reduction was carried out by mixing mill scale/CCC at 6:1 wt% ratio in high energy milling for 2 min. The mixture was pressed (100 MPa for 1 min) into pellets and sintered at 900 degrees C for 1 h and 1000 degrees C for 1 and 2 h under inert gas atmosphere. After cooling, the sintered pellets were crushed into powder and separated from impurities by magnetic separation. The results show that the reduction process is dominated by carbon gasification-diffusion from CCC. The improved metallization and better reducing process was more pronounced at 1000 degrees C for 2 h than that for 1 h with over 80 wt% being separated into metallic Fe and lesser CO2 trapped within the sample. X-ray diffractometry revealed that the intimate contact of mill scale/CCC was more increased in solid than that in powder state and indicated that the obtained phases are Fe, Fe3O4, and CO2. The presence of CO2 can be expected due to incomplete evacuation within the sample. These results suggest that mill scale/CCC has some promising potential on certain technical-industrial-scale applications, which might enhance their economic value after further research investigation and evaluation.