PURIFICATION OF PETROLEUM COKE HIGH IN SULFUR AND CONTAINING METALLIC IMPURITIES BY PASSING AN EXCESS OF SYNTHESIS GAS IN CONTACT WITH THE PREOXIDIZED COKE AT A TEMPERATURE AND PRESSURE AT WHICH THE CARBON MONOXIDE OF THE SYNTHESIS GAS IS CAUSED TO COMBINE WITH THE METALS, UNDER THE CATALYTIC EFFECT OF THE SULFUR IN THE COKE, TO FORM GASIFORM METAL CARBONYLS WHICH ARE READILY SEPARATED. THE RESULTING SYNTHESIS GAS IS THEN USED TO HYDRODESULFURIZE THE COKE UNDER APPROPRIATE CONDITIONS.