An ash-containing fuel feedstock comprising petroleum coke and/or heavy liquid hydrocarbonaceous fuel, wherein said ash comprises compounds of V, Ni, and Si in admixture with an iron-containing additive, is subjected to partial oxidation to produce a hot raw effluent stream of synthesis gas, reducing gas, or fuel gas with entrained molten slag. The hot raw effluent gas steam is cooled and coarse slag is separated. The coarse slag is heated to a temperature in the range of about 1900.degree. F. to 2600.degree. F. and above the melting point of said slag while in contact with reducing gas in a thermal reduction zone to produce a molten bath of slag comprising the following separable immiscible phases in wt. %.(a) a dense metal phase in the amount of about 0.1 to 5.0 which precipitates to the bottom comprising a nickel-iron alloy containing about 5 to 60 wt. % of nickel;(b) a sulfur encapsulated slag phase in the amount of about 5.0 to 85 that floats on said phase (a) comprising iron silicate;(c) the remainder comprising vanadium-rich silicate and spinel phases comprising at least 3 wt. % vanadium which floats on said phase (b). The three molten phases (a), (b), and (c) are then separated from each other.