Use of waste plastic as a reducing agent for iron ore
China's recent announcement that they will cease to accept large quantities of waste plastic has brought a growing crisis into sharp focus; global capacity for waste plastic handling is being rapidly outstripped by production. The clear solution is to find ways of profitably utilizing waste plastic, preferably involving total chemical conversion to non-persistent substances.
One possibility that has been previously neglected is that of using plastic instead of coal as a reducing agent for iron ore. The first criterion for a reducing agent is the chemical capacity to take up the excess oxygen atoms contained in hematite and magnetite. Polyethylene polymer has an effective chemical formula of (C2H4)n, and both Carbon and Hydrogen can be bonded to oxygen to form a range of stable compounds. The other criterion for a viable reducing agent is possessing sufficient chemical energy to drive the endothermic reduction of iron. Polyethylene has an enthalpy of formation of -(94.26n)kJ/mol and a Gibbs free energy of formation of -(36.44n)kJ/mol, giving it sufficient energy density for this purpose. In principle, therefore, it is perfectly viable to use waste plastic instead of coal for the reduction of iron ore.
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I think it is a bad idea to put plastic into a blast furance, it will be likely to melt and clog up the bed of iron ore and coke. I think it would be better to either recycle plastic by extrusion or to use a Lugi type plant to convert it into gas.
Mark Foreman · 29 Apr, 2018