A method of purifying a gas stream derived from a process wherein a glyceride containing raw-material is converted to hydrocarbon paraffins. The gas stream contains hydrogen or carbon dioxide as a major component and at least one sulphurous component selected from sulphide compounds as an impurity. According to the invention, the gas is contacted with an acidic aqueous wash solution of transition metal ions capable of binding to sulphide ions; a significant portion of the sulphide compounds contained in the gas are bound into practically insoluble transition metal sulphide compounds to remove sulphide compounds from the gas to produce a purified gas; and the obtained purified gas is recovered. The method will efficiently lower sulphide concentrations to ppm or sub-ppm level and it can be implemented on an industrial scale with low investment costs. The metal can be recovered.