Lanthanide phosphate solubility products

Most lanthanide compounds are sparingly soluble. Among those that are analytically important are the hydroxides, oxides, fluorides, oxalates, phosphates, complex cyanides, 8-hydroxyquinolates, and cup-ferrates. The solubility of the lanthanide hydroxides, their solubility products, and the pH at which they precipitate, are given in Table 2. As the atomic number increases (and ionic radius decreases), the lanthanide hydroxides become progressively less soluble and precipitate from more acidic solutions. The most common water-soluble salts are the lanthanide chlorides, nitrates, acetates, and sulfates. The solubilities of some of the chlorides and sulfates are also given in Table 2. 

The maximum concentration of tri valent elements like the lanthanides and Am would be determined by the solubility product of either the phosphate, the hydroxide or the carbonate (depending on the concentration of the corresponding anion and pH of the ground-water). Species in solution would largely be hydrolysis products, MC03 and possibly a small fraction of MF2+ and. A considerable part of the soluble fraction would be non-charged or anionic (28). 

Trivalent lanthanides are favoured under normal environmental conditions and many lanthanide(III) compounds are known. Many of the compounds are soluble but the hydroxide, carbonates, fluorides and phosphates are insoluble. Solubility products of some... 

A method is being developed to transform actinide ions in the near surface environment to less soluble, less reactive, thermodynamically stable phosphate minerals phases through application of organophosphorus complexants. These complexants decompose slowly, releasing phosphate to promote the formation of stable phosphate mineral phases, particularly with the more soluble trivalent, pentavalent, and hexavalent actinide ions. The complexant of choice, myo-inositol(hexakisphosphoric acid) or phytic acid, is a natural product widely used as a nutritional supplement. We have determined that phytic acid decomposes slowly in the absence of microbiological effects, that crystalline phosphate minerals are formed as a consequence of its decomposition, and that the formation of actinide (lanthanide) phosphates reduces the solubility of trivalent and hexavalent metal ions under environmental conditions. 

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