Reduction of Metal Oxides by Pyrolysis of Waste Polymers

This review evaluates the effectiveness of gaseous products derived from the pyrolysis of waste polymers (polyethylene (PE), polypropylene (PP), high-density polyethylene (HDPE) and waste tires) in reducing metal oxides (cobalt(III) oxide (Co₃O₄), nickel(II) oxide (NiO), bismuth(III) oxide (Bi₂O₃) and copper(II) oxide (CuO)). Owing to the high energy consumption and environmental impact of conventional reduction techniques, utilizing pyrolytic gases as an alternative reducing atmosphere is critical for sustainability and resource recovery. Experimental studies conducted using horizontal tube furnace systems have demonstrated that gas mixtures obtained from waste polymers — comprising mainly H₂, CH₄, C₂H₄ and aromatic hydrocarbons — can effectively reduce these metal oxides at relatively low temperatures. This review comparatively evaluates parameters influencing reduction efficiency, such as temperature, reactant ratio, heating rate, and gas composition, and provides detailed evaluations of product phases and microstructures through XRD, SEM, and EDS analyses. The findings reveal novel opportunities for waste management and sustainable metallurgy, establishing pyrolytic gases as a promising solution at scientific and industrial levels.