Physico-chemical analysis (X-ray, FFIR) and/or methanol oxidation reaction test were performed on fresh and deactivated vanadium catalysts used in H2SO4 manufacturing. It allowed the diagnosis of catalyst deactivation sources, as well as the processes of regenerating and recycling the worn out catalyst in converter. One of these processes is hydrometallurgical method. It consists in treating the deactivated catalyst with alkaline or acidic reagents and forming vanadate solution. A simple and non-costly operation of chemical attack permits the extraction of vanadium from silica in deactivated catalyst. The extracted vanadium can be used for the confection of regenerated catalysts or metallic tools. After optimization, this method can be used for industrial application. (C) 2003 Elsevier B.V. All rights reserved.