This thesis deals with a new process for the hydrometallurgical treatment of iron and zinc containing residues. In a precipitation step the zinc is ideally extracted from the hydrochloric solution as zinc hydroxide. In a following step it is then calcinated to ZnO under the formation of steam. In practical experiments however it has been observed that the zinc is actually precipitated as a zinc hydroxy chloride compound called tetra basic zinc chloride (TBZC) with the chemical formula Zn5(OH)8Cl2∙H2O. As a consequence of this losses of zinc up to 20 % were noticed upon calcination due to the evaporation of ZnCl2. Therefore, in the following different approaches are investigated in order to minimize zinc losses by the selective removal of chlorine. In this context, two main paths are investigated. On one hand the thermal route is examined, with the options of clinkering and pyrohydrolysis. On the other hand a hydrometallurgical treatment by the example of soda leaching for the dechlorination of TBZC is looked into. Both routes are evaluated by three steps, with the first step being a literary study on relevant aspects as well as similar residues these treatments are used for. Subsequently thermodynamic calculations are conducted in FactSage and Hydra in order to gain first insights into the reaction mechanisms at hand. Lastly, these calculations are validated by and compared to lab scale experiments. Additionally, an alternative process path for the precipitation is investigated to prevent the formation of TBZC. Both the untreated and the already hydrometallurgically treated zinc compound showed a change in appearance, upon thermal treatment losing its pure white color. Since the optical appearance is a major quality aspect for high purity zinc oxide, the causes for this shift in color are also investigated based on literature. Overall, both routes achieved satisfactory results with a separation of zinc and chlorine of 99 % for pyrohydrolysis in air and 98 % for Soda leaching at 80 °C. However, the results for the less complex setup of clinkering without water vapor only achieved separation of 85 %. Literature and thermodynamic calculations suggest that despite bad practical results, dry thermal treatment is also a promising path for dechlorination. While keeping costs low, higher zinc losses can be expected in parallel.