Soluble aluminum phosphate complexes

Phosphate precipitation of uranium (IV) is more selective. It is made from dilute hydrochloric or perchloric acid solutions. Separation is made from manganese, iron, vanadium and most other elements. Zirconium, thorium, and, to a smaller extent, titanium and tin precipitate.-Aluminum Interferes by the formation of soluble complexea with uraniiuii and phosphate lons. With sulfate and aluminum present, uranium is precipitated in a narrow pH-range around one. At higher pH, the soluble alumlnum-uranlum-phosphate complex is formed at lower pH, the soluble uranium-sulfate... 

What the high concentration of fluoride in the solution does is to induce the formation of a soluble tetracoordinated state of aluminum, which has the same geometry, size, and coordination as a phosphate. Among many metals tested in the presence of fluoride, Sternweis and Gilman [14] found that only beryllium could substitute for aluminum for the activation of adenylate cyclase. This fact reinforced the assumption that aluminum acts through its tetrahedral phosphate-like complex AlF4 1, because all beryllium complexes are tetracoordinated [16]. 

The small Al3+ cation with a high charge does not exist in the free form under physiological conditions. In mildly acid intracellular conditions, aluminum is bound to phosphate. Aluminum forms soluble salts with some acids, for example, with citric acid [82], or complexes with some compounds, for... 

Mono- and diammonium phosphate are used as solid fertilizers, whereas ammonium polyphosphate is mainly utilized in solution as a liquid fertilizer, since unlike the orthophosphates, it is very soluble and is more difficult to granulate than the orthophosphates. As a result of its complexing properties, it also keeps impurities (iron, aluminum, magnesium etc.) in solution. 

No information is available on the composition and structure of soluble precursors. We feel that observations made in buffered reaction mixtures are of particular value because the degree of polymerization of silicate and aluminosilicate is better controlled. Most of our experiments have been carried out in phosphate-buffered mixtures, and it has to be taken into consideration that phosphate is also a complexing agent for aluminum. 

Tnteraction of aluminum and phosphate has long been a problem of interest to soil scientists and water chemists. Many different precipitates have been prepared by mixing solutions of aluminum salts and phosphate (4, 5, 6, 17). Some of these precipitates are crystalline, but many others are amorphous. Some have definite stoichiometric compositions, but many others do not. Some are dissolved in IN HCl almost instantaneously, but others can be dissolved only after prolonged heating. On the other hand, the formation of soluble complexes of aluminum and phosphate has been suggested (3y 8,14). 

This report illustrates that and hydroxy-aluminum polymers react with phosphate differently. AP tends to form soluble complexes with phosphate, whereas the polymers can be precipitated by phosphate easily. Because a rapid equilibrium between AV and polymers does not exist, the reaction products will be dependent on the nature of aluminum species originally present in the solution. 

This class of membranes resemble those employed for dialysis or electrodialysis. However for the PM, transport selectivity is not based on the size of the permeating species or its charge, but on the specific solubility of complexes formed by the metd species and carrier in the membrane matrix. Effective separation of uranium from its mixture with iron and aluminum in dilute nitric acid was obtained with PVC sheets plasticized with TBP (57) and with dibutyl cresyl phosphate (DBCP) or dicresyl butyl phosphate (DCBP) (57,55) in a ratio of 1 3 (by weight). The U(VI) permeation... 

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