Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ivb metal
Patent
1987-01-02
1989-04-18
Stoll, Robert L.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ivb metal
423 85, 423545, 423548, 423520, 423608, 423DIG2, 106450, C01G 2500, C01G 2506
Patent
active
048225754
DESCRIPTION:
BRIEF SUMMARY
This invention relates to processes for the purification of zirconium compounds, to zirconium containing compositions which are intermediates for the preparation of high purity zirconium compounds, to processes for the preparation of said intermediates, and in particular to processes for the purification of zirconium dioxide (zirconia; ZrO.sub.2).
There is considerable demand for high purity zirconia for use in the electronics industry and in the production of partially stabilized zirconia. Much of the world's supply of zirconia is obtained from the naturally occurring mineral zirconium silicate (zircon; ZrSiO.sub.4) and processes currently used to extract zirconia from zircon in general involve the thermal decomposition of zircon to give zirconia and silica or the chemical decomposition of zircon to give zirconia and derivatives of silica. However, the crude zirconia produced in this manner requires purification by further chemical treatment.
Thermal dissociation of zircon to give a mixture of zirconia and silica offers an economically attractive route to zirconia. The dissociated zircon product can be leached with a strong base such as caustic soda in order to dissolve the silica and leave zirconia or can be leached with a strong acid such as sulphuric acid to dissolve the zirconia and form a zirconium salt leaving undissolved silica. The caustic-leach process produces zirconia which may have a purity as high as 99.5% but which must be subjected to further chemical processing (typically involving dissolving the zirconia in an acid) to produce high purity zirconia. The acid-leaching process has the advantage of procuding an acidic solution of a zirconium salt or a water soluble zirconium salt which may be further processed to produce high purity zirconium compounds including zirconia.
The most favoured acid-leaching process involves the dissolution of crude zirconia in sulfuric acid to give zirconium sulfate solution. The zirconium values may then be recovered by basification to precipitate the basic sulfate or hydroxide (hydrous zirconia). For example, U.S. Pat. No. 3,389,005 teaches the precipitation of zirconium hydroxide from zirconium sulfate solution by the addition of ammonia. However, in practice the precipitates formed in this manner are gel-like and difficult to filter and occlude many impurities. For this reason precipitation of the basic sulfate is preferred although, as discussed by Farnworth et al ("Specialty Inorganic Chemicals: The Production, Properties and Uses of Zirconium Chemicals", R. THOMPSON (Ed.), The Chemical Society, London, 1980 at page 257), it is difficult to control conditions to obtain optimum precipitation of the basic sulfate from zirconium sulfate solution. Therefore, the procedure often followed is the conversion of the zirconium sulfate to zirconium oxychloride and the precipitation of the basic sulfate by the addition of sulfuric acid or a sulfate salt as taught in Japanese Patent Application Publication No. 23975/69.
It has now been found possible to produce high purity zirconium compounds, including zirconia, by the precipitation of zirconium compositions from aqueous zirconium sulfate solution at a low pH. This method has the advantages that said zirconium composition may be precipitated directly from zirconium sulfate solution, the precipitate may be readily collected by filtration and said zirconium composition may be readily converted to zirconium chemicals, including zirconia, which have very low levels of metallic impurities.
Accordingly the invention provides a process for the preparation of zirconium compositions which on calcination form zirconia which process comprises:
preparing an aqueous zirconium sulfate solution having a pH not greater than zero;
adding an ammonia source to said aqueous zirconium sulfate solution until the pH of said solution is in the range of from 0.1 to 2.5; and
collecting the precipitated zirconium composition.
"Ammonia source" is used herein to mean anhydrous ammonia, aqueous ammonium hydroxide, ammonium salts and compounds and c
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College Chemistry an Introductory Textbook of General Chemistry, Linus Pauling, W. H. Freeman and Company, San Francisco, Calif., 1950, pp. 89 and 90.
Hartshorn Angus J.
Jenkins David H.
Ngian Kian F.
Harvey Paige C.
ICI Australia Limited
Stoll Robert L.
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