This paper deals with a method devised to concentrate and recover the zinc oxide present in Imperial Smelting Process slags. It is based on a preliminary refiring cycle, which enables the concentration of almost the whole of the zinc available in the slag in a newly formed phase, a magnetite—franklinite solid solution (Fe 3O 4ZnFe 2O 4), embedded in a glassy groundmass. The following sulphuric acid leaching treatment was found to exhibit a selective dissolving action, leaving most of the zinc-bearing phase as a solid residue. The laboratory procedure could be developed into a possible route for the complete utilization of Imperial Smelting Process slags. An overall recovery of about 85% of the total zinc available in the original slag was obtained after 8.5 hrs of leaching action of a 2% sulphuric acid solution at a temperature of 100°C.