Separation oxalate precipitation

Los Alamos is processing a wide variety of residues, including Pu-Be neutron sources, polystyrene-Pu02-U02 blocks, incinerator ash, Pu-U alloys and oxides, Pu-Zr alloys and oxides, Pu-Np alloys and oxides, Pu-Th alloys and oxides, etc. Processes have been developed for these scrap items (see Figure 2), but we need to know more about Pu-Np separations Pu-Th separations oxalate precipitations for both plus 3 and plus 4 valences valence stabilization dissolution methods for high-fired impure oxides in-line alpha monitors to measure extremely low concentrations of Pu and Am in HNO3 solutions and solubility of various mixtures of Pu02 and UO2 under a variety of conditions. 

Americium may be separated from other elements, particularly from the lanthanides or other actinide elements, by techniques involving oxidation, ion exchange and solvent extraction. One oxidation method involves precipitation of the metal in its trivalent state as oxalate (controlled precipitation). Alternatively, it may be separated by precipitating out lanthanide elements as fluorosilicates leaving americium in the solution. Americium may also he oxidized from trivalent to pentavalent state by hypochlorite in potassium carbonate solution. The product potassium americium (V) carbonate precipitates out. Curium and rare earth metals remain in the solution. An alternative approach is to oxidize Am3+ to Am022+ in dilute acid using peroxydisulfate. Am02 is soluble in fluoride solution, while trivalent curium and lanthanides are insoluble. 

The calcium levulate precipitate was separated from the reaction mixture by filtration and washed with cold water. The precipitate was suspended in water to give a thick slurry, and solid carbon dioxide added until the solution was colorless to phenolphthalein. A heavy precipitate of calcium carbonate was now present and free fructose remained in the solution. The calcium carbonate precipitate was removed by filtration, and the filtered solution was found to contain 1,436 g of fructose as determined by optical rotation. A small amount of calcium bicarbonate was present as an impurity in solution and was removed by the addition of oxalic acid solution until a test for both calcium and oxalic acid was negative. The insoluble calcium oxalate precipitate was removed by filtration. 

The process sequence currently used for waste salts (except those containing aluminum for which no process currently exists) is shown in Figure 1. The process includes (1) dilute hydrochloric acid dissolution of residues (2) cation exchange to convert from the chloride to the nitrate system and to remove gross amounts of monovalent impurities (3) anion exchange separation of plutonium (4) oxalate precipitation of americium and (5) calcination of the oxalate at 600°C to yield americium oxide. 

Plutonium Finishing. The separated plutonium was processed to Pu02 by conventional cation resin exchange, oxalate precipitation, and calcination methods. 

Americium is separated from iron, chromium, nickel, and other impurities by oxalate precipitation. The Am feed solution for precipitation in the MPPF after formic acid denitration and volume reduction was approximately 2 g Am/L, 14 g Cr/L, 1.2 g Fe/L, and 0.8 g Ni/L in 1M HNO3. Further concentration of the feed solution to >2 g Am/L necessitated evaporation at <85°C because of the potential corrosion of the stainless steel... 

Sr Precipitation of Sr and Ba as the nitrates from HNO3 solution. Separation of Sr and Ba by oxalate precipitation. 

Glendenin and Coryell in the fission products of uranium after separating the rare-earth fraction by oxalate precipitation. is produced with a fission yield of... 

Usually, Pm is separated from other lanthanides by ion exchange in the presence of complexing agents in solution. This method was also applied by Marinsky, Glendenin and Coryell in 1947 after oxalate precipitation of the rare-earth fraction, the precipitate was treated with carbonate solution to remove the main part of Y, dissolved and passed as 5% citrate solution (pH 2.5) through a cation-exchange column. The result is shown in Fig. 14.2. 

Postprecipitation Postprecipitation involves the formation of a second insoluble substance on a precipitate already formed, as a result of differences in rates of precipitation. For example, in the separation of calcium from magnesium by oxalate precipitation of calcium, the solubility of magnesium oxalate may be exceeded. But, since magnesium oxalate has a pronounced tendency to remain in supersaturated solution, it slowly precipitates on the caldiun oxalate over a period of many hours. 

We shall mention only some of the work in these fields. Vajda et al. (1991) have described a simple and rapid method for the separation and successive determination of total radiostrontium in soil by using a crown ether. The method consists of three basic steps oxalate precipitation to remove bulk potassium, chromatographic separation of strontium from most inactive and radioactive interferences utilizing a crown ether, oxalate precipitation of strontium to evaluate the chemical yield. Radiostrontium is then determined by liquid scintillation counting of the dissolved precipitate. When 10-g samples of soil are used, the sensitivity of the method is about 10 Bq/kg. The chemical yield is about 80%. The separation and determination of radiostrontium can be carried out in about 8 h. 

Oxalate precipitation experiments. Simulated and fully active HAW solutions have been utilized to carry out experimental tests on the separation of actinides by oxalates precipitation and on the actinide/RE separation steps. 

The Oxal process was initially tested by carrying out separately the HAW denitration and the oxalate precipitation. Results obtained from simulated and Wind-scale HAW solutions are in good agreement. The best DF for Am and Cm ( 2x 103) were obtained, however, on the Windscale solution, operating at about pH 2. 

To prevent during the denitration step the formation of precipitates on which Pu and Am were partially and irreversibly adsorbed, denitration and oxalate precipitation were carried out in a single step by addition of the waste solution to the formic and oxalic acid mixture, the latter acid acting as a metal complexant during the denitration step. By experimental tests performed on simulated HAW according to this modified process scheme, separation yields of about 99.5% for Pu and 99.8% for Am were measured. A further reduction of the actinide content was reached by flowing the clarified HAW solution through a Dowex 50 resin column. The oxalate precipitation experiments on fully active HAW solutions have practically been completed. The results obtained from five runs (Table IV) confirmed the previous results obtained on simulated solutions. 

The experimental equipment used in studying the continuous oxalate precipitation and the separation of the precipitate from the liquid is depicted schematically in Figure 3. The equipment allowed for options of filtering or settling the precipitate and the use of either one or two stirred tank reactors. The following variables were studied ... 

If plasma or whole blood is required for analysis, then the blood is collected in a tube containing an anticoagulant. Heparin (sodium salt) is frequently used. However, its effect is temporary and heparin is expensive. Therefore, a more widely used anticoagulant is potassium oxalate, about 1 mg per mL blood. Oxalate precipitates blood calcium, and the calcium is required in the clotting process. Obviously, plasma prepared in this way cannot be analyzed for calcium or potassium many other metals are precipitated by oxalate, and so serum is usually analyzed for these. The usual practice in preparing whole blood or plasma samples is to add the required amount of oxalate in solution form to the collection tube and then to dry the tube in an oven at 110°C. By this procedure, the collected blood is not diluted. For example, 0.5 mL of a 2% potassium oxalate solution would be taken and dried for a 10-mL blood sample. Potassium oxalate causes red cells to shrivel, with the result that the intracellular water diffuses into the plasma. Thus, the plasma should be separated as soon as possible. 

A solution of 27.3 g. of anhydrous ZnCls is in 200 ml. of water and 2.5 ml. of 2N HCl is prepared. Another solution, containing 31.3 g. of (NH4>3C304 H3O in 2.0 ml. of water and 2.5 ml. of 2N aqueous NH3 solution, is prepared separately. Both solutions are heated to 70 °C, and the oxalate solution is then poured in a thin stream into the vigorously stirred zinc salt solution. The oxalate precipitate is washed by decantation with water imtil it is free of chlorides. It is then placed on a filter and dried by suction. The ZnC304 2 H3O is then transferred to a flat pan which is placed in a drying oven. The temperature is then raised to 240 C over a period of 6 hours and is then maintained at this level for an additional 12 hours. This treatment removes nearly all of the water of crystallization. The anhydrous oxalate is then converted to ZnO by heating at 400°C for 4 hours. 

Adeeyinwo and Tyson [10] used a stainless-steel disc filter with 2 m pore size, 6 mm diameter, and 2 mm thickness to separate calcium from an interfering aluminium matrix by oxalate precipitation. The results were inferior to those obtained using membrane filters, giving poor reproducibility. These results are consistent with the experiences of Valcarcel et al.[7] using disc type stainless-steel filters mentioned above. ... 

Oxalate Calcium oxalate—CaC204 Precipitates actinides and rare earth elements. Can separate Ra from Pb, Bi, Po, and Ca at pH 2. That pH 3.5. Sr, Ba, and Y carriers precipitate as oxalates. Precipitates actinides from urine and leaves behind organics... 

After strontium carrier is added to a small volume (<10 ml) of °Sr solution, sufficient fuming nitric acid is added to attain a nitric acid concentration of 14-16 N. The solution with strontium nitrate precipitate is cooled in an ice bath and then centrifuged. The supernatant solution is thoroughly decanted and the strontium nitrate precipitate is dissolved in water. Barium and yttrium carriers are added. Precipitation of barium chromate at pH 5.5 removes and natural radium from the supernatant strontium solution (for counting, if needed, of these two separated radioelements). Precipitation of yttrium hydroxide in basic solution then removes the daughter that has grown into the °Sr parent. Ammonium oxalate is immediately added to the supernatant solution to precipitate strontium oxalate. The precipitate is washed and dried in the filter holder with alcohol and ether, promptly weighed for yield determination, and counted with a beta-particle detector (Chieco 1997) such as a proportional detector. 

For the analysis of lead in urine, the lead is often separated by precipitation as the phosphate in ammoniacal medium or as the oxalate, which is then ignited. The polarogram is finally run in tartrate or citrate medium, either acid or alkaline. 

Extraction of columbate-tantalates, titanocolumbates, and titanosilicates may also be initiated by treatment of the mineral with hydrofluoric acid. The procedure has the advantage that columbium, tantalum, uranium(VI), scandium, titanium, zirconium, and hafnium are dissolved, while silica is volatilized as silicon tetrafluoride and the rare earth elements, together with thorium and uranium(IV), remain as slightly soluble fluorides. The residue is then heated with concentrated sulfuric acid to remove hydrogen fluoride and to oxidize uranium (IV), the thorium is separated by precipitation of the phosphate (synthesis 12), and the rare earths are precipitated as oxalates. 

They also studied the separation of rare earths in phosphor wastes by chelating resins. The leaching was done in two steps (i) selective leaching with 1.5 kmol/m sulfuric acid in order to obtain (Y, Eu) fraction and (ii) leaching of its residue with 18 kmol/m sulfuric acid in order to obtain (La, Ce, Tb) fraction. For the mutual separation of the rare earths, the iminodiacetic acid and nitrilotriacetic acid-type resins were used for the (Y, Eu) and (La, Ce, Tb) fractions, respectively. After oxalate precipitation and calcination, each rare-earth oxides were obtained with the yields and purities, respectively, of 50% and 99.8% (Y), 50% and 98.3% (Eu), 30% and 96.0% (La), 30% and 87.3% (Ce), and 90% and 91.8% (Tb) (Takahashi et al., 1996). They applied solvent extraction with PC-88A to achieve mutual separation between yttrium and europium from (Y, Eu) fraction obtained by the selective leaching with 1.5kmol/m sulfuric acid. Mutual separation was achieved by the... 

An alternative American process uses a feed produced by oxalate precipitation of thorium and rare earths. This precipitate is calcined to the oxides and dissolved in nitric acid for extraction with undiluted TBP. After stripping with 8N nitric acid, a high proportion of cerium extracts with the thorium, but the other rare earths are eliminated. The cerium is then back-washed in a separate extractor by means of 0 1 N sodium nitrite solution, which reduces it to the solvent-insoluble cerous condition. Thorium is then backwashed in the last extractor with either water or 2 per cent sulphuric acid. In order to make this process economic it was necessary to devise an efficient system of oxalic acid recovery. This was based upon treatment of the thorium and rare earth oxalates with sodium hydroxide and recycling the resulting sodium oxalate to the precipitation stage. 

The general tendency to apply RNAA for the determination of trace elements when high sensitivity and precision are required can be confirmed. Methods have also been developed for multielement determinations by RNAA. These methods are generally based on complicated separation schemes and usually combine several individual procedures. Randa et al. (2003) reported a method for the determination of REEs, Cs, and Rb combining the REE separation based on oxalate precipitation with the Cs-Rb separation using ammonium molybdophosphate (AMP). Tian et al. (2001) published an RNAA method for the determination of REEs, U, and Ba consisting of a fluoride precipitation of REE and U, and a Ba sulfate precipitation. According to another RNAA method, U and Th determination was based on fluoride precipitation of the analyte nuclides (Np and Pa), while Sr was precipitated as sulfate. Combined procedures of Zaidi were briefly reviewed in O Sect. 30.5.3.1 (see also Zaidi et al. 2001). 

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