Oxalates, determination of, in rare

Oxalates, determination of, in rare earth oxalates, 2 60 Oxalato salts, tri-, 1 35 Oxides, reduction of refractory metal, to metal powders with calcium, 6 47... 

Probably the most important chemical procedure in the determination of the rare earths is the determination of total rare earths in some matrix which usually involves the precipitation of the rare earth oxalates and ignition to the oxides, R2O3. This procedure also serves to separate the rare earth group from other elements present in solution prior to the determination of the individual rare earths by other methods such as flame emission spectrometry. Chemical methods can also be employed to separate the light rare earth fraction from the heavy rare earth fraction with minimum difficulty. Chemical methods such as solvent extraction are also quite useful in the preconcentration of the rare earths where they are present at extremely low concentrations prior to their determination by other methods. 

Potassium pentachloronitrido-osmate(VI), 6 206 Potassium permanganate, solution of, standardization of, for determination of average atomic weight of rare earth elements in oxalates, 2 60, 61 Potassium pyrosulfite, 2 166 and its f-hydrate, 2 165, 167 Potassium rare earth sulfates, 2 47 Potassium selenocyanate, 2 186 Potassium sulfites, KHSO , in solution, 2 167... 

The classic method for the isolation of the rare earth group which is used for both qualitative and quantitative determination involves three methods. In the first method, rare earths are precipitated as fluorides in acidic medium. The elements precipitated include Mg, Cu, Fe, rare earths Th, Ca and Sr. The second method consists of precipitation as hydroxides resulting in the removal of alkaline-earth elements like calcium from the mineral. In the third method rare earths are precipitated as oxalates from moderately acidic solutions and the elements Ca, Zn, Pb, Cu, Cd, and Ag may be coprecipitated. In early times the above methods were repeated several times to isolate, the rare earth group in a relatively pure form. 

Atomic fluorescence spectrometry may be the most sensitive of the four techniques — particularly with laser assistance it has rarely been used with solid or slurry sampling and largely for determinations of metals in biological fluids, urine [105-107] and blood [106-110], Typical examples of solid sampling with this technique include the determination of Li in lithium oxalate [111], Ti in electrothermal atomizers [112], Pb and T1 in nickel-based alloys [113], and Co in high-purity tin [114],... 

Estimation. — The quantitative determination of thorium in a solution free from zirconium and the rare earth group is very simple. It consists of precipitating the hydroxide or oxalate and igniting to the oxide. In the presence of other similar salts the process becomes elaborate and usually involves several precipitations by the same or different reagents in order completely to remove interfering substances. Some of the more important methods of determination are outlined as follows —... 

Determination of the Oxalate Content. Two other duplicate samples of the oxalates of about 0.15 g. each are weighed out, transferred to 125-ml. beakers, dissolved in 20 ml. of warm 10 N sulfuric acid, diluted with 100 ml. of water, and titrated hot with 0.025 N potassium permanganate recently standardized against Bureau of Standards sodium oxalate or, better, against a rare earth oxalate of known purity. 

The radionuclide zirconium-95 ( Zr) can be found among direct products of nuclear fission. Its radioactive decay leads to the daughter niobium-95 ( Nb). In the determination of Zr and Nb in samples of seawater and sea plants, the samples are mixed with oxalic acid in order that zirconium and niobium complexes can be formed in the presence of nitric acid. The oxalic acid is destroyed with potassium chlorate, and zirconium and niobium are precipitated as zirconium phosphate and niobic acid, respectively. Activities of rare-earth elements are removed, and zirconium is separated as barium hexafluorozirconate and ashed to zirconium pentox-ide. The niobium fraction is ashed to niobium pent-oxide. Both radionuclides are finally determined by y-ray spectrometry. 

The second method, oxalate precipitation of rare earth standards, provides chemically bonded constituents. However, relative reproducibilities of 17 percent were obtained with this type of preparation, only slightly better than with dry blended standards. A source of error in attempting broad range quantification of different intensity levels is the fluctuation in the total ion beam composition at the beam monitor. Any determinations dependent upon relative exposure levels will include this error. 

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