Abstract A quantitative investigation of poly(vinyl) chloride (PVC) de-chlorination using Fe₂O₃, together with the impact of SiO₂ addition on the co-pyrolysis of PVC and Fe₂O₃, was conducted below 673 K in an Ar atmosphere aiming to cut the emission of gaseous Cl⁻ products. It was found that chlorine in PVC can be fixed in FeCl₂ by the reaction between PVC and Fe₂O₃. The co-pyrolysis of PVC and Fe₂O₃ proceeds in two stages with a temperature boundary of around 543 K. Below 543 K, a direct reaction occurs between PVC and Fe₂O₃, resulting in a small mass loss ratio and some extent of chlorine fixing ratio in FeCl₂. However, above 543 K, PVC starts to decompose to release gaseous H₂, HCl, etc., which react with Fe₂O₃ through two possible pathways to form FeCl₂. In Pathway 1, first Fe₂O₃ is reduced to Fe₃O₄ by H₂, followed by the chlorination of Fe₃O₄ to FeCl₂ by HCl. In Pathway 2, first Fe₂O₃ is chlorinated to FeCl₃ by HCl, followed by the reduction of FeCl₃ to FeCl₂ by H₂. The chlorine fixing ratio in FeCl₂ and the volatile generation ratio increase with decreasing PVC content in the initial mixtures. The addition of SiO₂ promotes the chlorine fixing ratio in FeCl₂ and volatile generation, and the impact gets stronger with decreasing PVC content in the mixtures. The chlorine fixing ratio is increased from 70.8 to 82.6% by SiO₂ addition for the mixtures containing 25% PVC, whereas the difference in the chlorine fixing ratio in FeCl₂ caused by SiO₂ addition is negligible for the mixtures containing 90% PVC. Fayalite (Fe₂SiO₄) was not detected in the solid residues after the experiments. After separating FeCl₂ using water leaching, the filter residue, a composite of iron oxide and conjugated polyene, can be used as a raw material for iron-making.