In the zinc smelter acid leaching process, sulfuric acid is added to the neutral leach residue until 45-60 g/L free acidity. Usually, this step is very efficient (92%). However, it also makes iron and others impurities soluble. Because of that, the solution must goes to some iron removal step (jarosite for example). In this work, we compared this method to the sulfatation process. By simulating the roaster gas outlet (8% of SO2), at 650C, in a fluidized bed reactor (2 kg/h), we were able to solubilize 92% of the Zinc, and only 16% of the iron. That means, no excess acid was required in order to obtain the Zinc, and less acid was spent with iron (smaller residue was obtained because hematite occupies 67% less mass than jarosite). With these results, we may improve acid balance, residue reduction, and raw materials consumption in a Zinc plant.