Extraction and separation of zirconium and hafnium using octanol

Abstract

Zirconium (Zr) and hafnium (Hf) metals have drawn considerable attention due to their various applications, especially in the nuclear industry where zirconium is used as a cladding material for nuclear reactors due its low neutron-capture cross-section and strong resistance to corrosion, whereas hafnium is used as an excellent control rod material for reactors due to its high neutron-absorption capacity. The efficiency of the reactor depends directly on the concentration of hafnium in zirconium. The zirconium should contain a very low concentration of hafnium, not exceeding 100 ppm, for use in the nuclear industry. Due to the fact that zirconium and hafnium occur within the same mineral, there is great interest in separating them in order to produce zirconium and hafnium oxide which can be used in the production of zirconium and hafnium metals appropriate for use in the nuclear industry. Hence, the separation and purification of these elements is of great importance. Solvent extraction techniques are employed to separate and purify these elements on an industrial scale. However, the separation of zirconium and hafnium is a difficult task as both elements exhibit similar chemical and physical properties. The main objective of this investigation was therefore to evaluate the potential of octanol as an alternative extractant to the conventional extractants methyl isobutyl ketone (MIBK) and tributyl phosphate (TBP) due to the problems associated with the latter two extractants. The effect of the different parameters affecting the extraction and separation of these two elements (Zr and Hf) were studied in terms of the initial feed concentration, contact time, extractants, loading capacity, temperature, diluents and stripping agents. It was determined from the results obtained that the different parameters investigated all have important effects on the extraction and separation of zirconium from hafnium. The results indicate that zirconium ions were preferentially extracted over hafnium with undiluted 1-octanol and 2-octanol in 10 % hydrochloric acid and 1.5 M potassium fluoride as feed concentration at a ratio of 1:2. The McCabe-Thiele diagram indicates that four equilibrium stages are required for almost complete extraction of zirconium from the aqueous solution. Sulfuric acid was found to be the most desirable agent for stripping zirconium from the loaded organic solution. A mixture of oxalic acid and nitric acid was considered to be a good stripping agent for hafnium as it could lead to good separation of hafnium from the remaining zirconium. Zirconium and hafnium were neutralized using 25 % ammonium hydroxide solution. After filtration and calcination, the products obtained were characterised using XRD and SEM-EDS analysis. A packed column was also used to compare the effectiveness of the extraction and separation of zirconium from hafnium. It was observed that in order to achieve the optimum mass transfer, greater column height is required.