Zirconium basic sulfate

In the initial thiocyanate-complex Hquid—Hquid extraction process (42,43), the thiocyanate complexes of hafnium and zirconium were extracted with ether from a dilute sulfuric acid solution of zirconium and hafnium to obtain hafnium. This process was modified in 1949—1950 by an Oak Ridge team and is stiH used in the United States. A solution of thiocyanic acid in methyl isobutyl ketone (MIBK) is used to extract hafnium preferentially from a concentrated zirconium—hafnium oxide chloride solution which also contains thiocyanic acid. The separated metals are recovered by precipitation as basic zirconium sulfate and hydrous hafnium oxide, respectively, and calcined to the oxide (44,45). This process is used by Teledyne Wah Chang Albany Corporation and Western Zirconium Division of Westinghouse, and was used by Carbomndum Metals Company, Reactive Metals Inc., AMAX Specialty Metals, Toyo Zirconium in Japan, and Pechiney Ugine Kuhlmann in France. 

Carbonates. Basic zirconium carbonate [37356-18-6] is produced in a two-step process in which zirconium is precipitated as a basic sulfate from an oxychloride solution. The carbonate is formed by an exchange reaction between a water slurry of basic zirconium sulfate and sodium carbonate or ammonium carbonate at 80°C (203). The particulate product is easily filtered. Freshly precipitated zirconium hydroxide, dispersed in water under carbon dioxide in a pressure vessel at ca 200—300 kPa (2—3 atm), absorbs carbon dioxide to form the basic zirconium carbonate (204). Washed free of other anions, it can be dissolved in organic acids such as lactic, acetic, citric, oxaUc, and tartaric to form zirconium oxy salts of these acids. 

Basic zirconium sulfates are formed by hydrolysis of zirconium sulfate, which is broken up into fragments that undergo further hydrolysis to yield a series of basic sulfates with the generic formula Zr (OH)2 2 ( 4 )n-i (190). 

Basic zirconium sulfate is also considered to be strands of [Zr(OH)2] joined by bridging sulfates (208). The resulting formula is Zr(OH) - (OH) (SO 3 -nH,0, wheie h are bridging anions and t are terminal anions. 

The crude tetrachloride mixture of zirconium and hafnium is dissolved in ammonium thiocyanate solution. The solution is extracted with methyl isobutyl ketone (MIBK). MIBK is passed countercurrent to aqueous mixture of tetrachloride in the extraction column. Halhium is preferentially extracted into MIBK leaving zirconium in the aqueous phase. Simultaneously, zirconium tetrachloride oxidizes to zirconyl chloride, ZrOCb. When sulfuric acid is added to aqueous solution of zirconyl chloride, the chloride precipitates as a basic zirconium sulfate. On treatment with ammonia solution the basic sulfate is converted into zirconium hydroxide, Zr(OH)4. Zirconium hydroxide is washed, dried, and calcined to form zirconium oxide, Zr02. 

Fig. 5.1.7 TEM images of as-prepared spherical particles of basic zirconium sulfate (a), those calcined at 600°C for 3 h (b), and basic zirconium sulfate particles coated with Y(0H)C03 (c). The coated particles were exposed to a high-energy electron beam. (From Ref. 15.)...

De Wet A process proposed for extracting zirconium from zircon in the form of zirconium sulfate tetrahydrate. The sodium silicate byproduct should be free from radioactive elements. The key to this process is the formation of an insoluble basic zirconium sulfate as an intermediate. Invented by W. De Wet in South Africa. 

Basic zirconium sulfates are unlikely to contain discrete complexes. Zr(0H)2S04 and Zr2(OH)2(S04)3(H20)4 have three-dimensional framework structures that feature hydroxo and sulfato bridges. 

The sodium silicate is removed by leaching in water, which at the same time hydrolyzes the zirconates to complex hydrated hydroxides of zirconia. These can be directly calcined to yield impure oxides, or further purified for example by treatment with sulfuric acid. The zirconyl sulfates formed are precipitated with a solution of ammonia to form the basic zirconium sulfate Zr50g(S04)2-JC H2O, and then calcined. 

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