A process for producing a purified synthesis gas stream from a feed synthesis gas stream comprising besides the main constituents carbon monoxide and hydrogen also hydrogen sulphide, HCN and/or COS, the process comprising the steps of: (a) removing HCN and/or COS by contacting the feed synthesis gas stream with a catalyst in a HCN/COS reactor in the presence of steam/water, to obtain a synthesis gas stream depleted in HCN and/or in COS; (b) converting hydrogen sulphide in the synthesis gas stream depleted in HCN and/or in COS to elemental sulphur, by contacting the synthesis gas stream with an aqueous reactant solution containing solubilized Fe(III) chelate of an organic acid, at a temperature below the melting point of sulphur, and at a sufficient solution to gas ratio and conditions effective to convert H2S to sulphur and inhibit sulphur deposition, to obtain a synthesis gas stream depleted in hydrogen sulphide; (c) removing carbon dioxide from the synthesis gas stream depleted in hydrogen sulphide, to obtain the purified synthesis gas stream and a gas stream enriched in CO2.