Different wastes are generated by the steel industry, among them the shredder residue (SR). The main source of chlorine in SR is the polyvinyl chloride (PVC), which makes the use of this residue in a thermochemical process a great challenge. In this context, the addition of CaO in the pyrolysis process can decrease the release of acid gases, especially HCI. The objective of this work was to evaluate the role of CaO and its influence on Chlorine during the thermochemical conversion of SR. A fixed-bed pyrolysis reactor was used and the following variables were evaluated using a 2(k) factorial design: temperature, heating rate, inert gas flow (N-2) and CaO/SR ratio. The chlorine retention in char was higher in the experiments conducted in the presence of CaO. A decrease of the metals retention in char was verified in the experiments conducted with CaO for the following metals: Co, Cu, Cr, Fe, Ni and Zn. Through the removal of chlorine, it would be possible to conduct the pyrolysis process at higher temperatures, increasing its energy efficiency (EE). Therefore, the necessity to remove chlorine from SR before the pyrolysis process is evidenced, since from this the use of CaO would contribute to the EE increase and the metals retention in char, and consequently with the global desirability increase. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.