Chemistry of inorganic compounds – Halogen or compound thereof – Ternary compound
Patent
1997-06-02
1999-09-28
Nguyen, Ngoc-Yen
Chemistry of inorganic compounds
Halogen or compound thereof
Ternary compound
423341, 423 82, 423608, C01G 2504
Patent
active
059583550
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
THIS INVENTION relates to the treatment of a chemical. It relates in particular to a process for treating a zirconia-based material.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
Not applicable
BRIEF SUMMARY OF THE INVENTION
According to the invention, there is provided a process for treating a zirconia-based material which comprises, broadly, reacting, in a reaction step, a zirconia-based material with aqueous hydrogen fluoride (HF), to produce a soluble fluorozirconic acid compound.
In one embodiment of the invention, the zirconia-based material may be zirconia. In another embodiment of the invention, it may be dissociated zircon (`DZ` or ZrO.sub.2.SiO.sub.2). In yet another embodiment of the invention, it may be a zirconia-containing component of dissociated zircon.
When zirconia is used, it may be a naturally occurring zirconium material such as baddeleyite. The reaction then proceeds in accordance with reaction (1):
Instead, when zirconia is used, it may be that obtained by any suitable thermal process.
The dissociated zircon, when used, can be that obtained by any suitable process, particularly a thermal process. Thus, for example, it can be that obtained by destroying the crystal matrix of zircon (ZrSiO.sub.4) by heating it to a high temperature in a plasma furnace or a plasma generator, under oxidizing, inert or reducing conditions. Zircon is a mineral which is abundantly available at relatively low cost, but is chemically inert. Thus, inert zircon mineral is rendered amenable to chemical processing in accordance with the invention, by means of said plasma dissociation. During plasma dissociation, zircon is dissociated into separate zirconia (ZrO.sub.2) and silica (SiO.sub.2) mineral phases, with the product commonly designated as dissociated zircon (`DZ`), plasma dissociated zircon (`PDZ`), or ZrO.sub.2.SiO.sub.2. Alternatively, the zircon can be processed in a transfer arc plasma furnace under reducing conditions effecting essentially the removal of the silica phase with essentially ZrO.sub.2, popularly designated fused zirconia, remaining behind.
Zircon normally contains radioactive elements such as uranium (U) and thorium (Th) and their decay product elements, as well as other common impurities such as Fe, Ca, P, Al, Mg and Ti. These elements are released in the process of the invention, but the process provides an effective manner of dealing with these elements. In particular, the process results in the generation of only relatively small quantities of radioactive element containing wastes. Wherever reference is made in this specification to U and Th as radioactive elements, this is to be interpreted as referring instead or additionally also to their decay products.
In one embodiment of the invention, the PDZ may be non-desilicated, in which case the reaction proceeds in accordance with reaction (2): +4H.sub.2 O (2)
In another embodiment of the invention, the PDZ may be partially desilicated, in which case the reaction to produce the fluorozirconic acid is also in accordance with reaction (2).
In yet a further embodiment of the invention, the PDZ may be wholly desilicated, in which case the reaction to produce the fluorozirconic acid is in accordance with reaction (1), as given hereinbefore.
The desilication of the PDZ can be effected by known means, such as caustic soda leaching. Wholly or partially desilicated PDZ is also known as `DPDZ`.
It is to be appreciated that whenever, in the reactions of the process of the invention, reference is made to hexafluorozirconic acid (H.sub.2 ZrF.sub.6), this includes the compound ZrF.sub.4.2HF.xH.sub.2 O where x can range from 0 to 5.
The concentration of the HF in the aqueous HF or HF solution may be in the range of 5-70% HF by mass. The reaction may be effected at a moderately elevated temperature, which may be
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Zeitschrift Fur Anorganische Chemie, vol. 141, 1924, pp. 284-288, XP 000567218 J.H. De Boer `Die Trennung Von Zirconium Und Hafnium Duch Kristallisation Ihrer Ammoniumdoppelfluoride` See pp. 287-288, no month.
Zeitschrift Fur Anorganische Chemie, vol. 97, 1917, pp. 73-112, Von Otto Ruff `Uber Die Herstellung Von Zirkongegenstanden` See pp. 110-112, no month.
Atomic Energy Corporation of South Africa Limited
Nguyen Ngoc-Yen
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