Carbothermal Reduction of Manganese Oxides by Coke and its Blends with Polymeric Materials

Polymeric material consumption consistently increases year to year. Thus, new methods for their utility after use are becoming increasingly important. This study investigates the reduction of the manganese oxides Mn3O4, and MnO in slag by blends of coke with high density polyethylene (HDPE) and rubber.The reduction of Mn3O4 was investigated to evaluate the impact of HDPE/rubber on the pre-reduction of manganese oxides to MnO at 1000°C. Studies into the reduction of MnO in slag were conducted to assess the effect of HDPE/rubber on both synthetic and industrial slags at 1500°C. To assess the impacts on the systems, data from infra-red gas analysis of the product gases CO, CO2, and CH4 was collected and, with LECO oxygen analysis, enabled an understanding of extents and rates of reduction. XRD, SEM, and EDS analysis informed on phase composition and morphology, interfacial reactions, wetting behaviours and reduction mechanisms taking place in the reduction system.From this research the major findings include:• Reduction of slag components by coke blended with polymeric materials showed an improvement in the extent of reduction of MnO and SiO2 to Mn, Si, MnxSiy and their carbides, compared to coke alone.• Presence of CH4 from devolatilised polymeric materials in the 1500°C slag system enabled faster initial reduction reactions, benefiting the overall system.• Presence of HDPE/rubber in the 1500°C slag system resulted in an increased wettability of the slag, compared to reactions with coke alone. This is an indicator of increased reaction rates, also enabling improved rates of reaction through improved contact between slag and solid carbonaceous materials.• Slag composition has a large impact on the 1500°C slag system. Industrial slags displayed greater extents of reduction, wettability, and rates of slag penetration compared to synthetic slags, primarily linked to higher slag basicity in industrial slags.• Reduction of Mn3O4 blended with coke and polymeric materials at 1000°C showed no distinct benefit in terms of rates and extents of reduction compared to reduction by coke alone. Even so, all samples displayed complete reduction to MnO within similar time periods.• Rubber blended samples enable the formation of MnS in both the 1000°C and 1500°C manganese oxide systems