Oxalate homogeneous precipitant

Calcium can be determined as the oxalate by precipitation from homogeneous solution by cation release from the EDTA complex in the presence of oxalate ion.28... 

Homogeneous precipitation may be more useful in precipitation separation of rare earths. This involves addition of reagents which release the precipitating agent slowly in solution. Addition of trichloroacetic acid and dimethyl oxalate in place of Na2CC>3 and... 

Anion or cation generation Anions can be generated slowly in solution to bring about homogeneous precipitation. Swift and Butler reviewed precipitation of the metal sulfides by use of thioacetamide or thiourea. PFHS of sulfides of cadmium, mercury, zinc, and nickel have been studied more recently by Swift and others. Phosphate can be generated by hydrolysis of triethyl phosphate, oxalate by hydrolysis of methyl oxalate, and sulfate by hydrolysis of diethyl sulfate or sulfamic acid. 

Following a suggestion by Penneman, Hermann demonstrated that a substantial separation of americium from lanthanum could be obtained by fractional precipitation of americium and lanthanum oxalates. The precipitation is effected in homogeneous solution the precipitant is generated by the slow hydrolysis of dimethyl oxalate. The oxalate precipitate is greatly enriched in americium (50% of the lanthanum can be rejected at each stage, with about 4% of the americium) [35]. 

Oxalates. Stable oxalates of Pu(III), Pu(IV), and Pu(VI) are known. However, only the Pu(III) and Pu(IV) oxalates are technologically important (30,147). Brilliant green plutonium(III) oxalate [56609-10-0] precipitates from nitric acid solutions containing Pu(III) ions upon addition of oxaUc acid or sodium oxalate. The composition of the precipitate isPu2(C20 2 10H2O. A homogeneous oxalate precipitation by hydrolysis of diethyl oxalate at... 

After preparing a homogeneous solution of the precursors, powder precipitation is accompHshed through the addition of at least one complexing ion. For PLZT, frequently OH in the form of ammonium hydroxide is added as the complexing anion, which results in the formation of an amorphous, insoluble PLZT-hydroxide. Other complexing species that are commonly used are carbonate and oxalate anions. CO2 gas is used to form carbonates. Irrespective of the complexing anion, the precipitated powders are eventually converted to the desired crystalline oxide phase by low temperature heat treatment. 

Precipitation of calcium oxalate may also be made from homogeneous solution either by use of urea as reagent or by the use of dimethyl oxalate. Both procedures lead to satisfactory separations from magnesium. 

It has been found that from a homogeneous solution the oxalate of samarium is preferentially precipitated over oxalates of other rare earths and yttrium falls behind all of them. Thus, in a separation process Sm is concentrated to a greater extent at the head section and Y at the tail section [45]. 

The same derivatization was applied to the HPLC determination of STR and DHS in milk. The comparison of HPLC and ELISA methods was also performed for DIHS. After removal of fat by extracting a milk sample with oxalic acid and centrifuging, proteins were precipitated with TCA. The supernatant was treated by SPE on a Cl8 column. The cartridge was washed with water, and the analytes were eluted with ion-pair in MeCN. The eluate was reconcentrated by evaporating and dissolving in water. Postcolumn reaction took place at 65°C. Recoveries were dependent on the concentration level and the batch of SPE columns used, and independent of the fat content and homogenization. The sample cleanup was not sufficient for the analysis of cheese. The DIHS concentrations of incurred samples determined by ELISA were higher than those obtained by the LC method (107). 

Control of Precipitate Formation. The problem with the character of the precipitated HML proved to be easily resolved with the particular lignin under study. When the addition of the glacial acetic acid was carried out at temperatures only as high as 50 °C, the reaction product was granular and did not retain large quantities of water in a semisolid mass. However, this condition required a redispersion of the solid after the oxalic acid catalyst had been added. This could be accomplished with mixers designed to homogenize and disperse materials in liquids. 

We have developed a thermal ionization method for use in a standard quadrupole mass spectrometer (1) The method uses a modified solids inlet probe Figure in conjunction with replacable filament assemblies The rhenium filaments are coated with calcium salts precipitated from biological materials in a basic ammonium oxalate solution Calcium is precipitated directly from urine and serum first made basic with ammonium hydroxide fecal samples and aliquots of diet are homogenized with a 9 1 water/nitric acid mixture, centrifuged, made basic and... 

Thermal decomposition also plays an important role in the conventional ceramic powder process, which makes use of starting materials such as metal carbonates that decompose during calcining, exposing reactive surfaces, which in turn aid in phase formation and chemical homogenization. Thermal decomposition is an important final step in solution preparation techniques. Precipitated hydroxides, carbonates, or oxalates are decomposed to oxides. Freeze-drying yields dried salts such as sulfates, which must be thermally decomposed to oxides. Similarly, many solution techniques use nitrates, which are decomposed as part of the process or in a separate step. 

The OXAL process. The flow-sheet of the Oxal process is shown in Fig. 3. The denitration is carried out by slow addition of the waste solution to the boiling mixture of formic and oxalic acid. The presence of the oxalic acid during the denitration prevents the polymerisation and precipitation of hydrolysable ions such as Zr and Mo ions, and assures the precipitation of the RE and actinide oxalates from homogeneous solutions in a we 11-crystallized form. After clarification, the supernatant is sent to vitrification and the oxalates are dissolved and destroyed by nitric acid so that a final solution (3M HN03) is obtained. 

Precipitation with oxalate at pH 3-4 separates calcium from metals which give soluble oxalate complexes [e.g., Fe(III), Al, and Ti], and also from phosphate. Calcium oxalate can also be precipitated from homogenous solution [11. 

To achieve homogeneity with these relatively solublecompounds, which, however, have different solubilities, the mixed formates must be prepared by a special spray-drying technique [31]. The mixed oxalates, which are precipitated with oxalic acid and ammonium oxalate rather than with alkali oxalates (this tends to give more active catalysts), yield, as a rule, homogeneous materials via a simple precipitation. Complex oxalates are just as usable as the mixed oxalates [33]. 

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