Microwave Production of Manganese from Manganese (IV) Oxide using Postconsumer Polypropylene as Reductant

Abstract

This work investigates the production of manganese metal from MnO₂ by microwave irradiation using postconsumer polypropylene (PP) as reductant. Reagent grade MnO₂ was first calcined to Mn3O4 followed by reduction with pulverised PP in a domestic microwave oven (Pioneer, Model PM-25 L, 1000 W, 2.45 GHz) in a recorded temperature range 900-1200 °C. Calcined and reduced products were characterised by XRD, XRF and SEM/EDX. The results showed that microwave irradiation is effective at calcining MnO₂ to Mn₃O₄, evidenced by the complete disappearance of peaks of MnO₂ and appearance of peaks of Mn₃O₄ after 40 minutes. SEM/EDX analysis revealed that calcined Mn₃O₄ was first transformed to MnO and later to manganese metal. The range of temperature achieved in the microwave oven was below the equilibrium temperature for MnO reduction by solid carbon and accordingly solid carbon produced from PP cannot be wholly responsible for the production of manganese metal. It is therefore concluded that the production of manganese metal observed in this investigation was effected with CH₄ (generated from the thermal decomposition of PP) and solid amorphous carbon as the predominant reductants, with solid amorphous carbon providing the heat energy required for the reduction. The reduction of manganese oxides using postconsumer plastics as reductants is therefore a potential route for diverting plastics from landfill sites as well as decrease the amount of expensive metallurgical coke currently used in the ferromanganese process.

Keywords: Microwave irradiation, Polypropylene, Calcination, Reduction, Manganese