US005437795A United States Patent 19 11 Patent Number: 5,437,795 Snyder et al. 45) Date of Patent: Aug. 1, 1995 (54) CHROMATOGRAPHIC SEPARATION OF 5,098,678 3/1992 Lee et al. .............................. 423/70 ERBUMISOTOPES 5,110,566 5/1992 Snyder et al. ......................... 423/70 5,124,023 6/1992 Bosserman . 210/659 (75) Inventors: Thomas S. Snyder, Oakmont; Steven 5,133,869 7/1992 Taniguchi. 210/659 H. Peterson; Umesh P. Nayak, both 5,174,971 12/1992 Snyder et al.......................... 423/70 of Murrysville; Richard J. Beleski, Pittsburgh, all of Pa. Primary Examiner-Ernest G. Therkorn 57 ABSTRACT 73 Assignee: Westinghouse Electric Corporation, Pittsburgh, Pa. A process for the partial or complete simultaneous sepa ration of isotopes of erbium, especially high thermal (21) Appl. No.: 264,810 neutron capture cross-section erbium isotopes, using 22 Filed: Jun. 23, 1994 continuous, steady-state, chromatography in which an (51) Int. Cl............................................... B01D 15/08 ion exchange resin is the stationary phase, an aqueous (52) U.S.C. .................................... 210/635; 210/656; solution of ions based on a mixture of erbium isotopes is 210/657; 210/659; 210/1982; 423/21.5; the feed phase, and an aqueous acid eluant solution is 423/263 the mobile phase. The process involves the mobile (58) Field of Search ............... 210/635,656,657, 659, phase eluting or desorbing the erbium isotopic solute 210/1982; 423/263, 21.1, 21.5 adsorbed on the stationary phase under conditions such that each of the various naturally occurring isotopes of (56) References Cited erbium is primarily eluted in an elution volume distinct U.S. PATENT DOCUMENTS from the elution volumes of the other isotopes. In a 3,582,263 6/1971 Chiola et al. ........................... 23/22 preferred embodiment, the conditions are such that at 3,615,173 10/1971 Winget ........... ... 423/21.5 least one of the elution volumes contains essentially 4,394,353 7/1983 Miyake et al. .. ... 423/21.5 only one isotope of erbium. The process is preferably 4,438,078 3/1984 Nalewajek. ... 423/21.5 conducted in a continuous, steady-state manner, and in 4,514,367 4/1985 Asami et al. ... ... 423/21.5 4,711,768 12/1987 Peterson et al. ... 423/21.5 particular is preferably conducted in a continuous annu 4,915,843 4/1990 Taniguchi....... ... 210/635 lar chromatograph (CAC). 5,024,749 6/1991 Snyder ........... 21.0/198.2 5,045,209 9/1991 Snyder et al. ....................... 210/656 13 Claims, 4 Drawing Sheets U.S. Patent Aug. 1, 1995 Sheet 1 of 4 5,437.795 U.S. Patent Aug. 1, 1995 Sheet 2 of 4 5,437.795 E; Y gNABS%% NEN NES ZZZZErnie 33: N SS: 3. 32 30 5 y 4,444 WW FIG 2 % 214 NNN N 60 U.S. Patent Aug. 1, 1995 Sheet 3 of 4 5,437.795 U.S. Patent Aug. 1, 1995 Sheet 4 of 4 5,437.795 5,437,795 1. 2 historical problems associated with ion exchange. These CHROMATOGRAPHC SEPARATION OF historical problems are: ERBUMISOTOPES 1. inherent batchwise operation; 2. awkward valving required for product recovery BACKGROUND OF THE INVENTION 5 when columns are operated in the chromato 1. Field of the Invention graphic mode; The present invention is concerned with processing 3. complex process control problems associated with erbium to obtain a lower average thermal neutron cap process operation and wave front separation; and ture cross section by a partial or complete separation of O 4. excessive product dilution associated with column its isotopes thus improving its suitability as an internal operation, and others. material of construction, for instance, as a fuel rod clad ding, for a nuclear reactor. OBJECTS OF THE INVENTION 2. Background Information It is, therefore, an object of the present invention to The role of erbium (Er) in nuclear fuel assembly 15 teach a separations art which overcomes these prob design is as a burnable poison with high neutron capture lems, which uses no hazardous organic solvents, and cross-section. Its properties are comparable or superior which consolidates purification and separation opera to Boron. Its chemical properties are similar to those of tions into a single operation. gadolinium (Gd) except that Er(III) is a slightly more It is also an object of the present invention to provide acidic ion than Gd(III) in solution; therefore, its separa- 20 a process for isolating erbium 167 which has a low tion chemistry should be somewhat more powerful than thermal neutron capture cross-section. that of Gd in a similar series of eluents. It is a further object of the present invention to pro The key issue in designing an enrichment system for vide a more efficient process than solvent extraction by the Er isotopic enrichment chemistry is that the key utilizing a chromatographic technique. fractions of the high cross-section isotopes are embed- 25 It is yet another object of the present invention to ded in undesirable isotopes. This results in the require provide a continuous technique for separating erbium ment of multiple extraction trains when using separa 167 utilizing a continuously operating chromatographic tions technologies such as solvent extraction or fixed technique. bed ion exchange columns which generically produce only "heads” and “tails” fractions but nothing in the 30 SUMMARY OF THE INVENTION "middle'. Hence, multiple trains are required to essen A process for the partial or complete separation of tially dissect the fractions until the desired head or tail the isotopes of erbium using chromatography has been emerges from the column as the sole constituent of the developed in which a cation exchange resin is the sta product fraction. When combining this enrichment tionary phase, an aqueous solution of an ionic com issue with the fact that Er separation from the ores 35 pound of a mixture of erbium isotopes is the feed, and an requires both complex chemistry and hardware, one aqueous acid solution is the mobile phase. The process arrives at the summary of issues that must be addressed by a process technology that recovers Er from the raw involves the mobile phase eluting the erbium isotopic ore and refines it to an isotopically pure product for solute under conditions such that each of the various inclusion in nuclear fuel assembly design: naturally occurring isotopes of erbium is primarily a. Separation of erbium from the other rare-earth eluted in an elution volume distinct from the elution elements and impurities in the ore leachate volumes of the other isotopes. In a preferred embodi 1. requires a large number of multi-stage extraction ment the conditions are such that at least one of the circuits due to relatively low specificity of distribu elution volumes contains essentially only one isotope of tion coefficients for most extraction solvents; erbium. The process is preferably conducted in a steady 2. requires a large number of large, awkward, expen state, continuous manner, and it is particularly preferred sive stages per extraction circuit due to the low to conduct it in a continuous annular chromatograph. magnitude of the distribution coefficients; A particular preferred embodiment involves feeding 3. generates hazardous and mixed wastes as a result of so erbium oxide dissolved in an aqueous mineral acid to a the organic based solvents; and continuous annular chromatograph with a stationary 4. requires significant peripheral purification opera phase which comprises a cation exchange resin. The tions to refine the erbium once it is separated from mobile phase for the elution is preferably aqueous hy the other rare-earths and to prepare it for isotopic drochloric acid, possibly with the addition of chelants, enrichment. 55 complexants, or ligands-particularly to the mobile b. Lack of a powerful, compact, cost-effective enrich phase chemistry-to enhance separation. However, ment process which, again, generates no hazardous sulfuric, nitric and specialized admixtures are all use waste as a byproduct. Solvent extraction is ineffective able. due to the inherently low separation alpha's (driven by the fact that trivalentions do not form readily separable 60 BRIEF DESCRIPTION OF THE DRAWINGS solution complexes), and to its large, capital-intensive, FIG. 1 is a perspective view of a continuous annular separation stages that increase both operating and main chromatograph (CAC) with a portion in section to tenance costs, generate hazardous process wastes (and illustrate the annular construction. possibly hazardous/radioactive mixtures depending on FIG. 2 is a longitudinal sectional view through the the composition of the original feed) and decrease pro- 65 CAC of FIG. 1. cess availability. FIG. 3 is a plan view of the bottom of the item shown c. There is a lack of a mechanically-feasible continu in FIG. 3, and ous ion exchange contactor design to overcome the FIG. 4 is a plan view of the bottom of the CAC. 5,437,795 3 4. and 1.0 milliequivalents per milliliter with a most proba DETALED DESCRIPTION OF THE ble capacity of about 0.1 to 0.5 milliequivalents per INVENTION milliliter under elution conditions. Styrene-based sul The process according to the present invention ef fonic and carboxylic exchangers meet this requirement fects the efficient and economical separation of high 5 as do certain phenolic and carboxylic resins. When neutron capture cross-section erbium isotopes from using anion exchanges, both weak and strong base resins mixtures containing erbium isotopes. Of particular in are possible; quaternary, tertiary and porous strong base terest is the continuous separation and isolation of the resins are preferred. 167Er isotope. It is also preferred that the stationary phase comprise The mixture that is treated according to the present O a monodisperse distribution of spherical particles with invention can comprise a mixture of erbium isotopes an average particle size of less than about 20 to 50 mi that has previously been separated from other rare earth crons, more preferably less than about 10 microns.