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The results of preliminary tests showed that it is possible to separate zirconium and hafnium in sulphate solution using high molecular weight liquid amines. Tertiary amines are considered to be the most promising extractants because of their high capacities. A separation factor of the order of 10 was obtained from an aqueous solution containing 10 g/l zirconium oxide and 0.2 g/l hafnium oxide at a pH value of 0.5 units using tertiary amines. 0.2 M organic solutions of tertiary amines have a capacity of approximately 6 g/l zirconium oxide. Alamine 336 has been selected for more detailed study. Substantially, complete separation of zirconium and hafnium was obtained in a five stage countercurrent experiment using alamine 336. Hafnium was not detected by spectrographic means in the organic phase of the final stage. The results of preliminary tests with fluoride solutions were inconclusive, revealing a lack of fundamental knowledge of the chemistry of zirconium and hafnium fluoride complexes in solution. However, these tests are to be repeated with modifications. The extraction isotherm of zirconium in sulphate solution extracted by tri-iso-octylamine was shown to correspond to the theory developed by Dr PJ Lloyd. A general theory of separation using liquid amines was developed and tests designed to prove its applicability are in progress.
The separation of hafnium and zirconium, required for nuclear use of zirconium, is generally performed by liquid-liquid extraction in organic solvents. The paper describes a new process based on extractive distillation of zirconium chloride (ZrCl4) and hafnium chloride (HfCl4) in a solvent made of molten potassium chloride-aluminum chloride (KCl-AlCl3) mixture above 350°C at atmospheric pressure. The corresponding process is now in full-scale industrial production.
A novel countercurrent liquid-liquid extractor is presented and illustrated with applications. The apparatus consists essentially of an assembly of mixer-settlers, feeders, reservoirs, and flow lines that are made of glass or other chemical resistant materials. The applicability of the extractor is illustrated by extractions involving zirconium and hafnium, and niobium and tantalum.
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.