Dissolved rare earth analyses

A significant proportion of the needs for reference materials for seawater trace metal studies would be addressed by the preparation of these materials. Although the total iron concentration of these reference materials should be provided, these materials clearly will be useful for studies of other important metals such as zinc, manganese, copper, molybdenum, cobalt, vanadium, lead, aluminum, cadmium, and the rare earth elements. With careful planning, such water samples should be useful for analysis of dissolved organic substances as well. The collection sites should be chosen carefully to provide both a high and a low concentration reference material for as many metals as possible. 

The simplest methods of HTSC analysis are based on the determination of the products of sample dissolution in acidic media. Potentiometric, amperometric, or coulometric titrations are frequently used (mainly for YBCO ceramics [525-527] and their analogs with other rare-earth elements [528, 529], and also for BSCCO [530]). We note particularly the method of potentiostatic coulometric analysis [531], which allows one to analyze thallium cuprate samples over a wide range of the Tl/Cu ratio, and also the method of flow-through coulometry for determining the effective valence of copper [532]. The polarographic determination of Cu content in the samples obtained by dissolving HTSCs in concentrated alkaline solutions with special... 

Trace levels of all of the rare earth elements (REEs) can be determined in rock samples and their distribution provides critical information to geologists. Some of the REE concentrations in basalt samples are in the sub-ppm range, but can be measured accurately in basalt samples that have been fused with lithium metaborate and diluted 5000-fold. The high dilution is necessary to keep the total dissolved solids <2000 mg/L, as the ICP-MS instrument does not tolerate high salt solutions well. The application is described by Ridd (see the bibliography). Use of ICP-MS for the REEs gives spectra that are simpler than those obtained by ICP-OES and all of the REEs can be measured, which is not the case with techniques such as neutron activation analysis. 

The typical purification method for rare earths is coprecipitation with ferric hydroxide, dissolution in dilute acid, precipitation as fluoride in strong mineral acid solution, dissolution in strong nitric acid with boric acid to complex fluoride, and precipitation for counting as the oxalate in dilute acid solution (Stevenson and Nervik 1961). Because Pm has no stable isotope, another rare earth (such as lanthanum) is added as carrier. The " Pm precipitate can be counted with a proportional counter, or can be dissolved and measured with an LS counter because of the low beta-particle energy. If small amounts of the other rare earth radionuclides are detected by gamma-ray spectrometric analysis, the beta-particle count rate of Pm can be calculated by difference. 

The decomposition of the ore sample by leaching and the liberation of rare earth elements to the leach liquor depends mainly on leaching temperatures as well as sulfuric acid concentration. Performing the leaching experiments at room temperature dissolve only 50% of the rare earth contents at 5M and 15M acid concentrations. The XRD analysis of the residue showed that relatively equal amounts of anhydrite and yttrium-fluorite were identified at 5M H2SO4. Increasing the acid concentration to 15M enhanced the formation of anhydrite to be double that of the yttrium fluorite in the sepai ated residue. This indicates that the reaction was not sufficient for complete decomposition of the ore sample. 

The solubility of rare earth perchlorates has also been studied in perchloric acid, thiourea water, urea water, and benzamide water systems (Korshunov et al., 1971 Karnaukhov et al., 1977 Ashikhnina et al., 1977 Osipova and Runov, 1981 Shchenev and Runov, 1981a,b). The solid compounds obtained were investigated by IR spectroscopy, differential thermal analysis, and X-ray powder diffraction. R(004)3 also dissolves in ammonia and R(004)3 and... 

When aqueous solutions of rare earth salts are treated with solutions of ammonium carbonate in hydrazine hydrate (N2H5COON2H3), rare earth metal hydrazine carboxylate hydrate complexes are formed [15]. Initially, a precipitate forms that dissolves with the addition of excess reagent. On keeping the solution for a couple of days crystalline solids separate. The crystals are washed with alcohol and then diethyl ether and stored in a vacuum desiccator. The composition of the crystals determined by chemical analysis and infrared spectra has been found to be Ln(N2H3C00)3-3H20 ... 

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