Uranyl borate

Uranyl Borate.—-Uranyl salts are precipitated by the addition of a solution of borax. ... 

Attempts to prepare uranyl borate from UO3 instead of U3O8 were only partially successful. The trioxide is more reactive than U3O8 and eliminates the necessity for an oxidation step in the metaborate synthesis reaction, but the low thermal stability of UO3 restricts the reaction temperature to <650°C. Infrared and x-ray analyses of products obtained after heating UO3 and B2O3 mixtures for several days at 650°C. indicated that only a minor conversion to the metaborate had been effected. 

Sodium uranyl borate is insoluble in water at 25°C. and gave no evidence of hydrolysis even after a five-day exposure to liquid water. The potassium salt showed slight evidence of hydrolysis in this time, as did the lithium salt. 

Figure 2. Infrared absorption spectra of sodium uranyl borate...

Table IV. Infrared Maxima (in cm." ) of Alkali Uranyl Borates...

TJew references to uranium borates appear in the literature. Larson (12) reported that yellow crystals, whose composition was assumed to be 3UO3 B2O3 (uranyl orthoborate), were obtained among other products from a melt of uranium niobate in boric oxide. Bruhat and Dubois (2) stated that perborate solutions react with uranium oxide to give an anhydrous stable yellow salt of the composition UBO4. No further information has appeared on either of these compounds. 

The spectra of LiU02B03 and KUO2BO3 are similar to the sodium salt spectrum—an indication that the uranyl and borate site symmetries are similar in the three compounds. 

It is also common for uranyl polyhedra to share their equatorial vertices with polyhedra containing other t5q)es of cations of higher valence. Where this is the case, the types of linkage are dependent upon both the size of the second polyhedron, and the charge of the central cation. For example, borate and... 

Walenta has described an unnamed mineral of Na, Mg, U, with borate and sulphate. A Ca, Mg uranyl sulphate has also been described by Kiss. Neither of these minerals has yielded sufficient information to characterize them adequately. A large number of synthetic uranyl sulphates have been described in the Powder diffraction file, some of which may well occur naturally. 

Keywords Aqueous speciation Bond valence Borate minerals Crystallization Dissolution Morphology Surface structure Uranyl minerals... 

Here, we have integrated many individual aspects of the growth and dissolution of minerals into a coherent description of these processes based on bond-valence theory and apply it to aspects of the morphology of uranyl-oxide hydroxyl hydrate and borate minerals. Below, we summarize the main aspects of this work ... 

In borate and uranyl-oxide hydroxyl-hydrate minerals, structural diversity occurs by polymerization of a small number of clusters (or fundamental building blocks). 

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