Ultrafast Chemical Separations (1993) / Chapter Skim
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2. Batch Processes
2. Batch Processes
Pages 6-34
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From page 6... ...
A short review of more recent fast radiochemical separations in the study of nuclei off the line of stability has been presented by Kratz, Trau~ann, and Henmann [Kra86] , and a summary of parts of this wow has been presented [Ren86al.
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From page 7... ...
These conditions are contradictory to the requirement for obtaining a pure solid phase [Gor591; also, these conditions will lead to crystals of small size that will not have the required filtration characteristics. Because of these limitations, precipitation has not been used extensively in fast radiochemical separations.
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From page 8... ...
Elements with fast procedures based on precipitation (shown with bold rectangles)
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From page 9... ...
Use of precipitation in radiochemical separation procedures. Element Reagent Timea Procedure # .
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From page 10... ...
This property has frequently been used in fast radiochemical separations to remove the activity of interest or contaminants from a solution. In the following subsections, we briefly discuss the applications of adsorption and exchange in fast radiochemical separation.
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From page 11... ...
, they showed that 50% of the silver activity present in 4-year-old fission-product solution can be exchanged win the silver chloride on a platinum gauze in about 20 s at 95°C. The information obtained from the studies referred to in the last few paragraphs was used in He incorporation of exchange techniques in fast radiochemical separations.
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From page 12... ...
In separation from fission products, filtration through freshly precipitated silver chloride has been used to remove bromine, iodine, and silver activities produced In fission. The procedure used for zirconium by Trautmann and coworkers [Tra721 and by Weis and Denschlag [Wei81]
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From page 13... ...
Hence, in the following subsections, use of the orgariic ion exchangers in radiochemical separations is discussed. The term "ion exchanger" is used specifically to refer to organic ion exchangers.
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From page 14... ...
For strongly acidic cation exchangers, He selectivity for He alkali metal ions is as follows: Li+ < Na+ < NH4+ ~ K+ < Rb+ ~ Cs+ For He trivalent lanthanides, it is ~ ''3+ ~ Yh3+ ~ am _ `~ _ .
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From page 15... ...
23~2 Application to Fast Radiochem~cal Separations Ion exchange is one of He most frequently used techniques, next to solvent extraction, in fast radiochemical procedures. The time constraint necessitates the use of flow rates and other conditions ~ are far from optimum.
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From page 16... ...
The following subsections give information on the applications of this technique to ultrafast radiochemical procedures.
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From page 17... ...
3, are some examples of reagents ~at can react with a number of metal ions to fonn uncharged chelate complexes. TTA, production of which was first reported by Reid and Calvin [ReiSO]
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From page 18... ...
The organophosphoric acids with replaceable hydrogen (e.g., H2MEHP, HDEHP) exchange hydrogen with metal ions and are known as liquid-cation exchangers.
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From page 19... ...
2-2TOPO, and ZrCl4~2TOPO. Among this group of extractants, TBP and TOPO are ~e two used most frequently in radiochemical separations.
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From page 20... ...
2.4~2 Application to Ultrafast Separations The liquid-liquid extraction technique has been applied in a wide variety of ways for a number of elements to achieve ultrafast separation. Figure 5 shows the elements for which one or more ultrafast separation procedures based on extraction are available in the literature.
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From page 21... ...
. Ultrafast separation procedures have been developed for some lanthanides using oxidation states other than +3 for the specific element or its parent.
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From page 22... ...
Fast chemistry procedures based on solvent extraction. Element Actinium Actinium Antimony Arsenic Arsenic Astatine Banum Bismuth Bromine Bromine Cadmium Cadmium Cadmium Cerium Cenum Cerium Copper Dysprosium Europium Gadolinium Gallium Gold Hafnium Indium Indium Indium Iodine Iodine Iron Lanthanides Lanthanides Lanthanum Lawrencium Lawrencium (from Md)
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From page 23... ...
. b Separation time is for the fastest procedure reported.
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From page 24... ...
However, he concluded that column efficiencies and separation time had to be improved. The separation time has been shortened sign~ficandy by the development of efficient adsorbent material for chromatographic columns, and by operation of ~e columns under high pressure.
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2.S.! Principle High-pressure liquid chromatography (HPLC)
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From page 26... ...
The entirety of the lanthanide fission products was separated in the cation exchangers column in less than ~ min. while any specific lanthanide could be separated In less than 3 min from the end of irradiation.
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From page 27... ...
It should be pointed out ~ the order of elusion Is reversed from Cat of a cation exchanger, He elusion order follows He atomic number. Horw~tz and coworkers [Hor'771 have investigated the applicability of extraction chromatography for the separation of lanthan~des.
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From page 28... ...
In addition to a general discussion of He technique, he has provided some detailed procedures and references to procedures in over radiochemistrv monographs. Applications of volatilization techniques to rapid radiochemical separations have been reviewed in death bY Amie} [Ami68]
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From page 29... ...
Elements for which a fast procedure based on volatilization is available (shown w~th bold rectangles)
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From page 30... ...
2.6, is the use of thermochromatography for He separation of different components that are volatilized under a given set of conditions. This technique has found a number of applications in fast radiochemical separations.
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From page 31... ...
Based on We results obtained and the theoretical mode} developed for the evaluation of adsorption enthalpies, they have predicted that vacuum thermochromatography can be used for fast chemical separations. It is important to recognize Cat the behavior of elements present at trace levels may be different from the behavior of the same element at macro levels.
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From page 32... ...
Kendall and coworkers have applied this technique for the separation of inorganic ions [Ken23, Ken251. The first radiochemical separation achieved using this technique was the separation of radium from barium [Ken261.
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From page 33... ...
s Zn-1 Zirconium Chloride <3 min Zr4 a Separation time is for the fastest procedure reported. Dunng the period 1950 to 1970, various researchers investigated the applicability of paper electrophoresis for the separation of inorganic ions.
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From page 34... ...
A number of fast radiochemical procedures using paper electrophoresis are available in the literature; however, such procedures are known only for a few elements, namely, selenium, bromine, strontium, cesium, banum, lanthanum, cenum, and praseodymium. The list of elements and Me separation times of procedures are for the separation of a specific lan~an~de from fission products.
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