Abstract: In the removal of sour gases, H.sub.2 S in particular, from CO-containing gaseous mixtures containing heavy metal carbonyls by scrubbing under pressure at temperatures of below 0.degree. C. with a scrubbing medium, the scrubbing medium is regenerated by inter alia, being heated by means of heat exchangers, and such exchangers are normally fouled by precipitates of metal sulfides which owe their presence to the decomposition of the metal carbonyls to form reactive heavy metal which combines with sulfide ion. To avoid fouling of the heat exchangers, the CO partial pressure is increased during the heating of the loaded scrubbing medium, to above the partial pressure of the CO in equilibrium with the carbonyls in the scrubbing medium thereby preventing the decomposition of the carbonyls.