The use of a process involving dissolution of a hardened chromium(III) oxide layer (4) in a warm aqueous solution containing an acid and an oxidising agent, during disintegration of a high temperature fuel cell stack, is new. Preferably, the solution contains 10 wt.% inorganic acid (preferably sulphuric or phosphoric acid) or organic acid (preferably citric acid) and 30 wt.% oxidising agent (preferably potassium permanganate) and dissolution is carried out at 60 deg C for about 8 hrs. with at least intermittent ultrasound application.
