Sodium zirconate

Oxide Chlorides. Zirconium oxide dichloride, ZrOCl2 -8H2 0 [13520-92-8] commonly called zirconium oxychloride, is really a hydroxyl chloride, [Zr4(OH)g T6H2 0]Clg T2H2O (189). Zirconium oxychloride is produced commercially by caustic fusion of zircon, followed by water washing to remove sodium siUcate and to hydrolyze the sodium zirconate the wet filter pulp is dissolved in hot hydrochloric acid, and ZrOCl2 -8H2 O is recovered from the solution by crystallization. An aqueous solution is also produced by the dissolution and hydrolysis of zirconium tetrachloride in water, or by the addition of hydrochloric acid to zirconium carbonate. 

Fusion with caustic soda at high temperatures forms water-soluble sodium zirconate ... 

The compound is prepared by dissolving zirconium tetrachloride, ZrCh, or sodium zirconate, Na4Zr04, in hydrochloric acid solution followed by evaporation to obtain crystals of octahydrate. 

This reaction is significant for sodium titanate (Keq — 10 moles /l ) and sodium zirconate, but is negligible for sodium niobate and some other "titanates" such as Mg(Ti205H)2. Gelatinous hydroxide precipitates which would appear likely based on Eq. 3 were not observed in the reaction of sodium titanate with aqueous waste, and stoichiometric loading was achieved with polyvalent cations which form insoluble hydroxides as well as for those forming soluble hydroxides. 

The work on hi level waste solidification has led to applications of the same materials to other areas of waste management. These include decontamination of defense wastes currently in tank storage at Richland, WA, selective separation of Cs for beneficial uses, and development of a process flowsheet for conversion of Zircaloy fuel cladding hulls to sodium zirconate for use in waste stabilization. Each is briefly described below. 

The Zircaloy Conversion Process (24, 25, 26) is a concept whereby one waste stream, Zircaloy fuel hulls, can be utilized in the stabilization of a second waste stream. The process flowsheet which is conceptual in nature, details the steps required to convert the fuel hulls to sodium zirconate to be used in the solidification of liquid high level waste. 

Sodium zirconate and sodium niobate exchangers have been prepared only in small laboratory-scale batches and their properties have been far less well characterized than those of... 

White, heavy, amorphous, odorless, tasteless powder nr monoclinic crystals. Also forms tetragonal crystals above — 1100° cubic above —1900". d 5.85. mp 2680°. bp 4300°. Practically insol in water slightly sol in HC1, HNO, slowly sol in HP dissolves on heating with a mixl of 2 parts HjS04 and 1 part H20. Fusion with sodium carbonate results in the formation of sodium zirconate which dec hydrolytically with water to form sodium hydroxide and practically insol zirconium hydroxide. 

Sorbents that are considered in the literature for sorption-enhanced reforming process are potassium promoted hydrotalcite (K-HTC), lithium orthosilicate (LiSi04), lithium zir-conate (LiZr03), sodium zirconate (Na2Zr03) and calcium oxide (CaO). The affinity of a sorbent to a molecule can be expressed by the equilibrium partial pressure at different temperatures. For example, the equilibrium partial pressure of carbon dioxide for different sorbents is shown in Figure 6.2. 

The cold frit is crushed in equipment which is preferably totally enclosed to prevent personal contact with the irritant alkaline dust. Leaching is then carried out with water to remove sodium silicate and excess sodium hydroxide. About 7 tons of water per ton of zircon are appropriate, this quantity being divided between several successive leaching operations. Solid-liquid separation is by decantation between each leach. The sodium zirconate is finally filtered off in a fairly dry condition. It is advisable not to use a larger excess of water or peptization of colloidal zirconium com-... 

It is more important to remove small amounts of silica from the sodium zirconate but this is retained in close association with the solid, probably as a sodium zirconium silicate, until it is subsequently dissolved in acid. Cold 12 to 16N nitric acid or ION hydrochloric acid is used, but the dissolution is accompanied by a considerable increase in temperature ... 

Then the sodium zirconate is dissovled in concentrated hydrochloric acid ... 

To date, a number of candidate CO2 sorbents have been investigated, including Ca-based oxides (CaO), potassium-based hydrotalcites, lithium silicates (LiSiOJ, and sodium zirconate (Na2Zr03) [53]. The reversible carbonation/ decarbonation reactions are ... 

Simple ABO compounds in addition to BaTiO are cadmium titanate [12014-14-17, CdTiO lead titanate [12060-00-3] PbTiO potassium niobate [12030-85-2] KNbO sodium niobate [12034-09-2], NaNbO silver niobate [12309-96-5], AgNbO potassium iodate [7758-05-6], KIO bismuth ferrate [12010-42-3], BiFeO sodium tantalate, NaTaO and lead zirconate [12060-01 -4], PbZrO. The perovskite stmcture is also tolerant of a very wide range of multiple cation substitution on both A and B sites. Thus many more complex compounds have been found (16,17), eg, (K 2 i/2) 3 ... 

This dissociated zircon is amenable to hot aqueous caustic leaching to remove the siHca in the form of soluble sodium siHcate. The remaining skeletal stmcture of zirconia is readily washed to remove residual caustic. Purity of this zirconia is direcdy related to the purity of the starting zircon since only siHca, phosphate, and trace alkaHes and alkaline earth are removed during the leach. This zirconia, and the untreated dissociated zircon, are both proposed for use in ceramic color glazes (36) (see Colorants for ceramics). 

Research work carried out at the Mechanobre Institute in Russia involved the evaluation of cationic and anionic collectors [8], The anionic collectors examined included sodium oleate and sodium alkyl sulphate. The results obtained indicated that with the use of sodium oleate, both zircon and pyrochlore can be floated with good recoveries (Figure 22.3). 

Flotation of pyrochlore using sodium alkyl sulphate is dependent on flotation pH. At a pH above 5.5, no pyrochlore flotation is achieved. At this pH, microcline, limonite and aegirine were floated. It appears that the use of alkyl sulphate at slightly acidic to alkaline pH number of gangue minerals can be selectively floated from pyrochlore. At a pH between 1.5 and 3.0, alkyl sulphate floats pyrochlore and zircon, whereas floatability of limonite, microline and aegirine is greatly reduced (Figure 22.4). 

Monazite is readily floatable using cationic collectors such as oleic acid and sodium oleate in the pH region of 7-11. Monazite does not float readily using, for example, laurel amine or anionic collectors. Adsorption of the sodium oleate on the monazite increases with an increase in pH, indicating that monazite does not float in acid pH, while pyrochlore is readily floatable and is depressed at a pH greater than 10. Figure 24.1 shows the effect of pH on flotation of monazite, pyrochlore and zircon. 

Limited research work has been conducted on these ores, but have indicated that REO cannot be recovered using either fatty acid or sodium oleate. It was, however, found that a mixture of sulphosuccinamate and phosphate ester modified with alkylsulphate can recover REO and zircon efficiently. Figure 24.5 shows the effect of above collector mixture (KBX3) on REO recovery from complex RE0-Zr02 ores. Oxalic acid and fatty acid (FA3) were not so effective compared to collector KBX3. 

India has very large deposits of monazite on the coastal shores of Kerala and Chennai. A typical mineral composition of this type of deposit is 60% ilmenite, 1.2% rutile, 5% zircon, 6.4% garnet, 4% silinanite, 16% quartz, 2.5-5% monazite and 1-7% shell. Research work involved different anionic collectors and pH during monazite flotation, along with the level of sodium silicate used as depressant. 

Experimental work conducted at different levels of sodium silicate (Table 24.9) indicates that sodium silicate is an excellent depressant for titanium, zircon and other gangue minerals while the monazite flotation is not affected. 

FIGURE 2.8 X-ray diffraction pattern for the preparation of zircon, ZrSi04, from zirconia, ZrOz, silica, Si02, and sodium halide mineralisers. The peaks demonstrate zircon to be the main product containing traces of all the starting materials. 

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