The present invention describes a process for treating a leaching residue generated in a leaching of a sulfur-containing metal concentrate. Therein, the leaching residueisfed into a reactor, wherein a fluidizing gas is injected into the reactor to form a fluidizedbed containing at least a portion of the leaching residue. So, the leaching residueis heated in the presence of inert particles to a temperature between 600 and 900 °C in an oxidizing atmosphere to produce calcined particles and SO2. At least 60 wt-% of the inert particles are removed from the fluidized bed while at least 60 wt-%of the calcined particles are removed together with a gas stream containing off-gases and the fluidizing gas.