Utilisation of post-consumer plastics in pre-reduction of higher manganese oxides in ferromanganese process

The pre-reduction of higher manganese oxides with post-consumer plastics as reductants has been investigated through experiments conducted in a laboratory scale horizontal tube furnace coupled with an off gas analysis through an online infrared (IR) gas analyser. Composite pellets of calcined manganese oxide (Mn₃O₄) with high density polyethylene (HDPE) (at C/O molar ratios of 1·5, 2·0 and 3·0) were heated rapidly to 1150°C under pure argon and the off gas was measured continuously by an IR analyser for CO, CO₂ and CH₄. The extent of reduction of Mn₃O₄ to MnO was calculated from a mass balance for removable oxygen. Solid reaction products were characterised by scanning electron microscopy and X-ray diffraction analysis was used to confirm the presence of MnO. The results indicate that Mn₃O₄ can be successfully pre-reduced to MnO using HDPE as a reductant. Gas analysis studies indicated that the polymer is first converted to CH₄ which cracked partially or reformed to H₂, C and/or CO. Reduction of Mn₃O₄ to MnO was subsequently effected by C, CO, H₂ and the residual CH₄.