Zirconium extraction studies with

For the purpose of improving the decontamination factor (DF) of FPs from U or Pu in the reprocessing of highly irradiated fuels such as those from FBR, a modified method adding inactive zirconium or hafnium ion is proposed. The feasibility of this concept has been experimentally demonstrated by both batchwise extraction and process studies with miniature mixer-settlers. 

This paper follows on from the early work by these authors (see discussion of [74TRI/SCH] in this Appendix). In this and the earlier work, the authors used the solvent extraction technique with y isopropyltropolone to study the complexation of Zr. In this work, they studied the complex formation of zirconium with chloride, thiocyanate, sulphate, oxalate and phosphate. On the basis of their earlier work, they proposed that reactions of the type... 

A mixture of well-known extractants, di-(2-ethylhexyl)phosphoric acid (HDEHP) and CMPO, in n-paraffin was used for the study of combined extraction of different actinides (americium, plutonium, and uranium) and lanthanides (cerium and europium) and their separation from fission products (cesium, strontium, ruthenium, and zirconium).54 Combined extraction of MAs and lanthanides was studied together with group separation of MAs from lanthanides by selective stripping with a solution of diethylenetriaminepentaacetic acid (DTPA), formic acid, and hydrazine hydrate. This solution strips only MAs, leaving lanthanides in the organic phase. Subsequently, the lanthanides are stripped using a mixture of DTPA and sodium carbonate. 

Golub et al. have shown that zirconium(IV) and hafnium(IV) form eight-coordinate complexes in solution with NCS" alone or in the presence of DMF 329, 333). The compounds (Et4N)2[M(NCS)8] (M = Zr, Hf) both contain iV -thiocyanato groups, as determined by infrared studies, and are isomorphous 61). Benzyl phenyl arsinic acid has been used as an extractant and, unlike most systems, hafnium complexes are extracted better than zirconium complexes in the presence of NCS" 302). 

In early studies, di-(2-ethylhexyl) phosphoric acid (DEHPA) had been chosen as the extractant (22). DEHPA extracts americium from the solutions of low acid concentrations such as 0.1 M, while a small percentage of americium is carried with the precipitate formed by denitration of the HLW with formic acid for acidity adjustment. At the end of the denitration, the pH of solution has to be kept lower than 0.5 to avoid the loss of americium more than 0.1 % due to coprecipitation with zirconium, molybdenum and tellurium. 

Extraction with triphenylarsine oxide in CHCI3 followed by the reaction with Arsenazo III (after stripping of the analytes with 4 M HCl) makes a basis of the determination of Zr and Hf (and Ti) in minerals and alloys [1], Sequential liquid-liquid extraction and spectrophotometric determination of zirconium(IV) with calixarene hydroxamic acid and thiocyanate has been described [2]. Colorimetric determination of Zr and Hf with Xylenol Orange and a liquid-liquid extraction of thenoyltrifluoroacetone complexes using H2O-IBMK has been studied [3]. 

Although alizarin-S (l,2-dihydroxyanthraquinone-3-sulfonate) has been used (162) for many years for the detection and estimation of zirconium and hafnium, the composition of the product formed in this system is still uncertain. Eecent studies on hafnium (43) and zirconium (317, 419) complex formation by spectrophotometric methods led to the conclusion that the zirconium 1 1 complex exists in the pH range 1.0-1.8 at a metal concentration of 1 x 10 M. Below that pH no complex could be observed and above that pH only suspensions were obtained. Hafnium, on the other hand, is said to form the 1 2 ligand complex at metal ion concentrations of (2 to 4) x 10 mole/liter over the pH range 1.0 to 4.0. A stability constant of 10.3 0.3 was reported for this species. The 1 1 complex of zirconium is extractable with i-butanol (149a). 

Conniek and McVey [49CON/MCV] measured the extraction of zirconium into benzene as Zr(TTA)4, in the presence of chloride. Only two measurements were taken and were used to indicate the formation of ZrCP. However, due to the inadequacy of the number of data points used to derive the stability constant of the speeies, it has not been included in this review. Levitt and Freund [56LEV/FRE] studied the solvent extraction of zirconium with tributyl phosphate (TBP) in the presence of chloride (6.54 M HCIO4 25°C). They did not determine the stability of the zirconium chloride complexes formed but their data were subsequently used by [57SOL] as the basis for a determination of the stability constants for four complexes ZrCl, o = 1 to... 

A study of the complexation of zirconium by hydroxide, sulphate, fluoride, chloride and nitrate using the solvent extraetion teehnique. Experimental work was conducted at (25.00 0.05)°C and in 2.00 M HCIO4. Benzene was used as the organic phase and thenoyltrifluoroacetone (TTA) as the extractant. Most experiments were performed with trace concentrations of Zr, imposed by using carrier-free Zr combined with careful purification from its decay product Nb. Some control experiments were performed with inactive Zr at higher Zr concentrations of 3 x 10 to 10 M. A few experiments performed in 2 m HCIO4 contained 0.1 M Zr. 

This is a study of the separation of zirconium and hafnium using a hydrochloric acid solution with benzene containing trifluoroacetylacetone (TTA). The study varied the concentration of both the metal and hydrochloric acid concentrations. Qualitative estimates of the stability constants of both zirconium and hafnium were given. For the hydrochloric acid data, a plot of MD, where D is the extraction coefficient, against the chloride concentration gave a linear fit (see Figure A-6) indicated that only ZrCI is present in solution (in the chloride concentrations used). 

This is a study of the complexation of zirconium by hydroxide using the potentiometric and solvent extraction techniques. The potentiometric experiments were conducted at 25°C and the solvent extraction experiments at 20°C. All experiments were conducted using 4.0 M CIO4, with the proton concentration being varied at 0.5, 1.0 and 4.0 M. 

This is a critical review of zirconium complexation at 25°C for fluoride and hydroxide ions. A combination of solubility and solvent extraction experiments together with electrostatic studies and modelling predictions was used. 

Meier et al. (20) studied this method very thoroughly zirconium is dissolved without warming up in a mixture of sulphuric and hydrofluoric acid under addition of a small amount of mannite to avoid losses of boron. The solution is then oxidized with some hydrogen peroxide and allowed to stand for 12 hours to decompose the excess of hydrogen peroxide. The further procedure is the one described in detail for the determination of boron in aluminium, except that here a pH value of 1.2 has to be used and the extraction is carried out in the presence of some hexamethylenetetramine. 

The repeatability of the micro Kjeldahl method was studied by Rodgers and Harter (10). In this method 1 g of zirconium is dissolved by heating in a 100 ml distillation flask with 25 ml hydrochloric acid (1+1) to which 15 drops hydrofluoric acid (48 %) have been added. After the addition of 15 to 20 ml sodium hydroxide (60 %) to the extraction solution, the ammonia formed by dissolving the sample is steam-distilled into a 50 ml Messier cylinder. The distillation takes 6 minutes. One ml Messier reagent is then added, and the solution is diluted to 50 ml with ammonia-free water. The yellow colour of the solution is determined photometrically. Unfortunately, no mention of blank values is made, which very much diminishes the value of the results. 

Noren (1973) studied the hydrolysis of both hafnium(IV) and zirconium(IV) at 25 °C and in 4.0 mol NaClO using potentiometric and solvent extraction methods. The data for zirconium have been combined with other available data at... 

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