Oxalate lanthanide compounds

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. 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

The solubility properties of curium(111) compounds are in every way similar to those of Ihe other tripositive Actinide elements and the tnpositive Lanthanide elements. Thus the fluoride and oxalate tire insoluble in acid soluliun, while the nitrate, halides, sulfate, perchlorate, and sullide are all soluble. 

The zinc reduction of Eu + to Eu +, followed by its precipitation as the sulfate, is a traditional step in the separation of europium from other lanthanides. In general, the solubilities of the inorganic compounds of the Ln + ions resemble those of the corresponding compounds of the alkaline earth metals (insoluble sulfate, carbonate, hydroxide, oxalate). Both europium and the Sm + and Yb + ions can also be prepared by other methods (e.g. electrolysis), although these solutions of the latter two metals tend to be short-lived and oxygen-sensitive in particular. Eu + is the only divalent aqua ion with any real stability in solution. Several divalent lanthanides can, however, be stabilized by the use of nonaqueous solvents such as HMPA and THE, in which they have characteristic colors, quite distinct from those for the isoelectronic trivalent ions on account of the decreased term separations. 

Although it might be assumed quite reasonably that the coordination chemistry of the some 15 elements known during Werner s lifetime would have developed significantly during that period, the literature contains only a few accounts of synthesis and characterization. Indeed, the 1920 edition of Werner s classic monograph (50) records essentially the same information as the 1908 edition, namely the compositions of a limited number of double nitrates, sulfates, and oxalates. Both Spencer ( 5) and Little in their comprehensive compilations of data at about the same time, describe only certain lanthanide double salts and adducts, but not within the framework of complex compounds or coordination chemistry. 

Experimental studies were therefore directed to investigate the removal of actinides from both diluted (5000 l/t) and concentrated (about 500 l/t) HAW solutions. Three alternative processes have been selected for this purpose. They all rely upon actinide separation at low acidity conditions requiring a preliminary denitration step. Two of them (TBP and HDEHP processes) are based on solvent extraction techniques using as extractants a neutral (TBP) and an acidic (HDEHP) organophosphorus compound respectively. The third process (OXAL) applies as the first step the precipitation of actinides and lanthanides FP as oxalates. 

Neodymium oxide was first isolated from a mixture of oxides called didymia. The elemeut ueodymium is the secoud most abuudaut lanthanide elemeut in the igneous rocks of Earth s crust. Hydrated neodymium(III) salts are reddish and anhydrous neodymium compounds are blue. The compounds neodymium(III) chloride, bromide, iodide, nitrate, perchlorate, and acetate are very soluble neodymium sulfate is somewhat soluble the fluoride, hydroxide, oxide, carbonate, oxalate, and phosphate compoimds are insoluble. 

This method has been realized for synthesis of perovskite solids. Precursor compoimds with anions as oxalates, acetates, cyanides, nitrates, hydroxides have been employed as precursors for the perovskite synthesis. Examples are LaCoOs from LaCo(CN)6.5H20 and LaNiOs and NdNiOs from tri hydroxide of lanthanide in both examples can be a substitution of cations (lanthanides or transition elements), LnFeO 3, (Ln = Er, Sm, Nd). Sometimes in this method, it is necessaiy to find a suitable precursor compound for the synthesis of the desired composition because it is limited by the stoichiometric ratio of cations in the preciu or and in the final oxide. [32, 33, 44]... 

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