The present invention relates to a method for the selective separation and recovery of metal solutes from an acidic aqueous solution by solvent extraction techniques. The present invention further relates to the selective separation and recovery of hafnium and zirconium metal solutes; of niobium and tantalum metal solutes; and of the platinum group metal (hereinafter referred to as "PGM") solutes from solution by the use of membrane based solvent extraction. According to one aspect thereof, the present invention provides a method for the selective separation and recovery of hafnium and zirconium metal solutes from an acidic aqueous solution, the method including the steps of: a) providing an acidic aqueous solution, the acidic aqueous solution including a source of at least two metal solutes wherein the at least two metal solutes are selected from the group consisting of hafnium and zirconium; b) contacting an organic medium with an aqueous stripping solution to form a water-in-oil emulsion; c) introducing the water-in-oil emulsion to a lumen side of a hollow fiber membrane contactor; d) introducing the acidic aqueous solution to a shell side of the hollow fiber membrane contactor; e) allowing one or more metal solutes to be transferred from the acidic aqueous solution to the water-in-oil emulsion; f) recovering a first metal solute from the water-in-oil emulsion; g) optionally, repeating any one or more of the steps described herein above where the recovery of a second and/or further metal solute is required; and h) optionally, repeating any one or more of the said steps where the purity of the first, second and/or further metal solute is desired to be improved. The present invention further provides for hafnium and zirconium metal solutes; of niobium and tantalum metal solutes; and of the platinum group metal solutes, recovered by the method of the present invention, substantially as described herein.