THE UNIVERSITY OF MICHIGAN INDUSTRY PROGRAM OF THE COLLEGE OF ENGINEERING RADIOCHEMICAL SEPARATIONS: I. Barium, Strontium, and Calcium Duane N. Sunderman W. Wayne Meinke September, 1955 IP-133

ACKNOWLEDGEMENT We would like to express our appreciation to the authors for permission to give this prepaper limited distribution under the Industry Program of the College of Engineering.

RADIOCHEMICAL SEPARATIONS: Io BARIUM, STRONTIUM, AND CALCIUM Duane No Sunderman and W. Wayne Meinke Department of Chemistry, University of Michigan Ann Arbor, Michigan ABSTRACT A program of critical evaluation of radiochemical separation procedures has been instituted. Procedures for individual elements reported in the literature are collected and subdivided into individual separation steps. Those steps which are found unique and possessing general applicability are studied experimentally to determine optimum conditions (of both yield and contamination) for separation. These procedures are then further evaluated under optimum conditions to determine the effects on the separation of a number of diverse but representative elements and materials. The alkaline earth elements, barium, strontium, and calcium were the first elements studied in this manner. Several common precipitations were studied to determine the conditions for optimum radiochemical separation within this group. It was found that conditions of operation must vary widely from commonly accepted analytical methods due to the demands of such factors as nonequilibrium operation, necessity for rapid precipitation, character of the precipitate, and manipulatory techniques. Nitrate, chromate and chloride precipitations were studied to give quantitative information concerning the contributions of these factors. Yield data are given for calcium, strontium and barium in the above separations under conditions varied to show the effects of excess or deficiency of reagents, quantitative or nonquantitative 1

precipitation and methods of adding precipitating reagents. Decontamination factors were determined with tracers of 16 typical elements. An optimum procedure is given for the systematic separation of these three ions in tracer S6lutions. INTRODUCTION Radiochemical separation procedures are composed of those chemical separation steps which, when applied to radioactive mixtures, yield a chemical species of sufficient purity to be uniquely counted or detected by the use of existing equipment and present-day techniqueso These procedures may include extraction, precipitation, ion exchange, electrolysis or volatilization stepso Separation may be required from a large variety of diverse elements, as in the case of fission product analysis, or from neighboring elements in the periodic table, as in procedures following bombardment by low energy (a few Mev) nuclear particles. In many cases interfering activities must be reduced by a factor of 104 to 106 or more but the yield of the desired activity does not have to be quantitative. Often the nuclear characteristics of the isotope desired are such that the separation must be completed rapidly. The general inorganic-analytical literature (26, 51, 53), while quite detailed in many cases, is not directly applicable to radiochemical work where nonequilibrium conditions are the rule rather than the exceptions A program of critical evaluation of radiochemical separation procedures has thus been instituted at the University of Michigan. In this program, certain groups of elements are being studied, procedures previously reported in the literature are being evaluated, and the most promising separation steps are being explored in detail to determine optimum conditions for high decontamination and yield. 2

LITERATURE REPORTS The first elements that have been explored are the alkaline earths: barium, strontium and calcium. Since barium and strontium are high yield fission products, considerable work has already been done on their radiochemical separations. By comparison, few radiochemical separation procedures are reported in the literature for calcium. Typical procedures for the separation of these elements are suggested by standard analytical references (26, 51, 53). These references have been supplemented by the experimental work of Willard and Goodspeed (68) who used nitric acid for the quantitative separation of barium and strontium from calcium. To determine the separation, procedures favored in recent work a complete survey was made of the nuclear chemical literature. Compilations of radiochemical procedures (5, 18, 33, 35, 36, 44) were consulted for separations involving these three elements, A number of references were located in the German literature (37), and additions to these detailed procedures were made from references for the isotopes of barium, strontium and calcium listed both in "Table of Isotopes" by Hollander, Perlman and Seaborg (28) and in "Nuclear Data" compiled by the National Bureau of Standards (67). References to all of these procedures are included in the Bibliographyo The literature search indicated that the separations of primary interest for these three elements were the precipitations with nitric acid (1, 3, 4, 6, 7, 11, 15, 199 21, 24, 26, 27, 39 42, 44, 45, 59, 60, 62 -65) *ammonium dichromate (1, 7, 10, 11, 16, 19, 21, 24, 25, 27, 34, 39, 40, 42, 45, 61, 65), and hydrochloric acid (7, 8, 9, 10, 11, 12, 15, 16, 19, 23, 34, 35, 39, 44, 55, 61)o Sulfate (23, 25, 47, 48, 58) and oxalate (1, 4, 11, 17, 20, 27, 29, 35, 38, 45, 46, 54, 65, 66) precipitations were also included in this study since they are widely used as a final step for the preparation of material for measurement. 5

Applications of solvent extraction or chelation (57) to these separations were not promising, and although good separations have been mdde by ion exchange (41, 63), time considerations prevent their general applicability to this work at the present time. Certain other minor methods involving precipitation of carbonate or 8-hydroxyquinolate (2, 13, 30, 43, 49, 50, 56, 64) were also found. Scavenging steps, involving precipitation of hydrous oxides of iron (III) or lanthanum (III), while often found in the procedures (1, 7, 10, 11, 13, 17, 19, 20, 21, 23, 27, 29, 35, 42, 45, 46, 54, 60, 61, 65, 66), will not be considered here. EXPERIMENTAL PROGRAM Precipitation separations are conducted under conditions which are standard in laboratories engaged in fission-product and bombardment work (18, 33, 35, 36, 44). In all cases, commercially available equipment is used. The carriers are added to a clean 15 ml centrifuge cone, radioactive tracers of these carrier elements are added, and the necessary steps taken to secure exchange. (In all the decontamination and yield studies on the alkaline earths 10 mg of carrier was present with the tracer.) Reagents are added to adjust conditions for precipitation, the precipitant is added, and the solution is stirred manually and digested for five minutes. The tubes are then centrifuged for five minutes at top speed, and the supernate is removed by use of a glass tube connected to a vacuum flask and through a trap to a water aspirator (a "slurp" tube). The precipitate is slurried onto a stainless steel plate to be dried and mounted, and then counted with a Geiger-Miller tube or transferred to a glass culture tube to be counted in the scintillation well counter. In radiochemical separations, it is important to know the behavior of elements quite dissimilar from the desired constituent under the conditions of the separation. The spectrum of dissimilar elements present in a mixture 4

may be quite broad and in some cases may include as many as 50 different species. In order to have sufficient information at hand to choose a separation for a given decontamination requirement, a number of representative elements were chosen to indicate the behavior of their respective groups. The elements used in these decontamination studies are shown graphically in Figo 1. APPARATUS AND REAGENTS Apparatus International Clinical Centrifuge. Centrifuge cones, 15 ml, borosilicate glass. Planchets, 1 in,.-diameter stainless steel, No. E-24, Tracerlab, Boston, Mass. Geiger tube, halogen quenched, 1.4 mg/cm2 window, Model D-34, Nuclear Instrument and Chemical Corporation, Chicago, Illo Scaler, Nuclear Instrument and Chemical Corporation, Model 163, scale of 128 (used with Geiger tube). Scintillation well counter, Nuclear Instrument and Chemical Corporation, Model DS-3 with 2-ino additional lead shieldo Scaler, Nuclear Instrument and Chemical Corporation, Model 162, scale of 128, used with well counter, modified to count with preset time and preset count and to reset automatically. Lead housing for Geiger tube, Technical Associates, Glendale, California, No. Al 14A. pH Meter, Beckmann Instruments, Pasadena, California, Model H. Reagents Ammonium dichromate solution (B and A reagent No. 1274), 100 g/l in water. Buffer solutions, sodium acetate (B and A reagent No. 2191) and acetic acid (B and A reagent No. 1019) (22). Fuming nitric acid 90-95% HN03 (B and A reagent No. 1121), analyzed by the pycnometer specific gravity methodo Hydrochloric acid: ether reagent, 4 volumes HC1 (B and A reagent No. 1090) to 1 volume ether (Mallinckrodt reagent No. 0848). 5

Sulfuric acid solution (B and A reagent No. 1080) H2S04, 10% by volume in water. Ammonium oxalate reagent (B and A reagent No. 1307), saturated solution in water. Hydrochloric acid, dry gas (Matheson, 99.0%). Carriers Antimony: SbCl3, MW 228.13, (B and A reagentNo. 1369), 10 mg/ml Sb(III) in dilute HC1. Barium: Ba(N03)2, MW 261.38 (B and A reagent No. 1420), 10 mg/ml Ba(II) in water. Calcium: Ca(N03)2 * 4H20, MW 236.16 (Mallinckrodt reagent No. 4236), 10 mg/ml Ca(II) in water. Cerium: Ce(N03)3, MW 434.25 (B and A reagent No. 1560)y 10 mg/ml Ce(III) in dilute HN03. Cesium: CsC1, MW 168.37 (Fotte Mineral Co.), 10 mg/ml Cs(I) in water. Chromium: Cr(N03)3 9H20, MW 400.18 (B and A reagent, No. 1578), 10 mg/ml Cr(III) in dilute HN03. Cobalt: Co(N03)2 * 6H20, MW 291.05 (B and A reagent, No. 1597), 10 mg/ml Co(II) in dilute HNO. Iodine: NaI, MW 149.92 (Mallinckrodt reagent No. 1139), 10 mg/ml i(-i) in water. Iridium: IrC14, MW 334.94 (American Platinum Co., Ir metal) 10 mg/ml Ir(IV) in dilute HC1. Ruthenium: RuC13, MW 208.07 (Fisher reagent No. R-322), 10 mg/ml Ru(III) in dilute HC1. Selenium: H2Se03, MW 128.98 (Fisher reagent No, A-286) 10 mg/ml Se(IV) in dilute HC.l Silver: Ag(N03) MW 169.89 (Merck reagent No. 2169), 10 mg/ml Ag(I) in water. Strontium: Sr(N03)2, MW 211.65 (Merck reagent, No. 748.94), 10 mg/ml Sr(II) in water. Tantalum: K2TaF7, MW 392.08 (Fisher reagent, No. T-17), 10 mg/ml Ta(V) in 0.5 M HC1 and 0.5 M HF, made up immediately before use, Tin: SnCl2 ~ 2H20, MW 225.65 (Merck reagent No. 7488), 10 mg/ml Sn(II) in 5% HC1. Zirconium: ZrO(N03)2 2H20, MW 267.26 (Fisher reagent No. Z-82) 10 mg/ml Zr(IV) in 0.5 M HN03 and 0.1 M HF. 6

Tracers Table I outlines the characteristics of the tracer solutions used for the yield and decontamination determinationso Daughter activities are listed with the parent. The valence states given in the table are either those listed in the Isotopes Division Catalog (32) or are those most stable for the conditions under which they were received. To minimize losses from hydrolysis or adsorption, dilutions of the tracers were made with solutions similar to those in which they were received. Small losses from hydrolysis or adsorption are not generally noticeable, because the materials are standardized at each use and small changes are ignored, but considerable loss did occur in silver by absorption on the walls of the soft glass bottleso Carrier-tracer exchange required individual attention for each element. Multiple valence elements and those readily complexed were given special attention. Cr51 From results of a study of the chromium(III)- chromium(VI) exchange, it was found that a negligible amount of the chromium tracer existed in the hexavalent form. Trivalent carrier was used throughout. Ir'92 Iridium tracer was obtained in a chloride complexed form, and the carrier was also kept in this form prior to mixing. Ru106 The ruthenium obtained from Oak Ridge National Laboratory was found totally in the reduced trivalent form, and no special treatment was necessary for exchange. Sb124 The tracer antimony was used as received, trivalent antimony carrier added, the mixture oxidized to the pentavalent form with bromine and theh-reduced. with hydrazine. A domparison of the'solution.obtained-'in this manner with that.obtained 7

by thorough mixing showed only minor differences in the contamination studies of the alkaline earth separations. Separations specifically requiring either the tri- or pentavalent antimony were not studied. Sn113 To assure exchange, the tin carrier was added as the divalent ion and oxidized to the tetravalent ion with hypochlorite in the presence of the tracero Ta182 Tantalum tracer is present as the potassium tantalate in KOH solutions. The carrier, potassium heptafluotantalate, was added to the solution of the tracer, hydrochloric acid was added, and the solution was warmed to complete solution of the heptafluotantalateo Exchange was presumed complete since the procedure involved heating in the presence of the complexing fluoride ion. This presumption was further supported by the fact that all the tantalum activity in contamination studies was found to accompany the macro amount of tantalum. Zr95 In all cases, zirconium tracer was separated from its niobium daughter by precipitation of barium fluozirconate, and the zirconium was separated from the barium by two precipitations of zirconium hydroxide (36). Complete exchange between carrier and tracer zirconium took place during the treatment with HF and precipitation of the fluozirconate. Special attention must be paid to the decay schemes and radiations of the tracers as well as to their chemical characteristics if the decontamination results are to be reproducible. Table II summarizes these nuclear characteristics (8). The scintillation well counter is suitable for measuring most tracers having gamma rays or high energy beta rays, but a thin window G-M counter is required for tracers emitting weak beta rays. Where activities fromcdaughter products would interfere with the counting of the parent, two methods were possible. In one, a suitable time (ten half 8

lives) could be allowed to elapse after the separation prior to counting. This time elapse would allow the mixture to reach equilibrium, i.e., where the parentto-daughter activity ratio would be constant. In the second method, the daughter activity would be removed by suitable precipitation steps and the parent activity would be measured before the daughter activity would again become appreciable. The first method was used in all experiments with the Ce-Pr, Ru-Rh and Sn-In pairs and in some experiments with the Ba-La and Sr-Y couples. Other samples of barium, strontium and all those of zirconium were counted by use of the second method. Growth and decay curves for the mixtures used in this work are presented in Figs. 2-8. From these curves, an evaluation can be made of the errors in the measurement introduced by daughter activities. Thus, it can be seen that following separation of the daughter, Zr remained sufficiently pure for counting purposes for several days, while barium and strontium had to be counted within two to four hours. EXPERIMENTAL PROCEDURES Six different precipitation procedures applicable to one or more of the alkaline earths were explored in detail to determine whether the procedures could completely carry macro amounts of these elements. Additional experiments were run to determine the contamination of the precipitates by other typical trace elements. Chromate Separation The classical method for the separation of barium from strontium is that of the precipitation of the chromate with ammonium dichromate from an acetate buffered solution (26). When there are few interferring elements that are not easily hydrolyzed, the precipitation can be made under more alkaline conditions in the region of Ph 7-8. The precipitant is added slowly to a relatively large volume of hot solution and the solution digested for one or two hours 9

after precipitation is complete. In recently reported work (31) a pH of fire has been used successfully. In this work precipitations-were macde from solutions maintained at a pH of four, five, and six (22). The conditions are not those in which equilibrium is established since precipitation is rapid, the experiment is conducted at room temperature, arn only a five-minute digestion time is allowed; however, quantitative yields are not required. To determine interferences, a complete separation of barium carrier from strontium carrier was made in duplicate for each contaminant under optimum conditions (pH 4). Ten mg of carrier plus the tracer for the contaminating element were used in these determinations. The itemized procedure is as follows: 1. Add ten mg barium carrier and barium tracer to 15 ml glass centrifuge cone. Mix thoroughly to effect exchange. 2. Add ten mg amounts of carrier and tracer of contaminating element to be studied,'e.g., Sr, Ca, or Co, Ru, etc, and take steps necessary to secure exchange. In cases where the yield of barium is not to be determined, the barium carrier (without tracer) is added last. 5. Add ten ml of acetic acid-sodium acetate buffer solution of the desired pH. Stir thoroughly. 4. Add two ml (NH4)Cr207 solution with stirring. Digest with occasional stirring at room temperature for five minutes. 5. Centrifuge at top speed for five minutes. 6. Remove supernate with slurp tube. 7. For geiger counting, transfer the precipitate by pipet to a stainless-steel planchet; then dry, mount and count. For scintillation counting, transfer to a glass culture tube, stopper and count in well countero Yields obtained with this procedure are shown in Table III. Table IV shows the results of the contamination experiments at pH 4. For comparison, the barium, strentium and calcium yield data are included in this table. 10

Nitric Acid Separation The insolubility of barium and strontium nitrate in strong nitric acid has been known for many years, but, in 1936, Willard and Goodspeed (68) made a thorough study of its analytical applications. Its applicability as a method for separation of barium and strontium from fission products was recognized early in the atomic energy program, and this method occurs quite frequently in the manuals of the National Laboratories (18, 335 35, 44). Three different concentrations of nitric acid (87%, 70% and 60%) were used to determine the effect of nitrate concentrations on the separation from calcium. The following procedure was used. 1. Add ten mg carrier and sufficient tracer of the contaminating ion (e.g., Ca or Co, Ru, etc.) to a clean 15 ml centrifuge cone and take steps necessary to secure exchange. 2. Add carrier solution containing ten mg each of barium and strontium. (Also add barium or strontium tracer when determining their yield.) 3. Add sufficient fuming HNOs and water to secure the desired concentration of HN03 (total volume 10-15 ml). Stir thoroughly. I!. Digest for five minutes at room temperature with occasional stirring. 5. Centrifuge for five minutes at top speed. 6. Remove the supernate by decantation to waste storage for HN03. Explosions! are likely to occur, if this solution is mixed with other wastes that may contain organic compounds. 7. Prepare the precipitate for counting. The results of the above procedure for barium, strontium and calcium are given in Table III. To account for the different uses to which this procedure might be put, decontamination studies were conducted with the representative elements of Table I using both the 80% and the 60% HNO3 conditionso Ten mg of carriers were used for all contaminants. The results are given in Table IV. 11

Hydrochloric Acid Separations Another method for the separation of barium from strontium, calcium and other elements is based on the insolubility of BaCl2 ~2H20 in strong HC1 solutions. Many variations of this method have been used in atomic energy work (7, 12, 44). Two of the techniques most often applied are: (a) the use of an ether: HC1 solution of about 7~5 to 8,5 M HC1 as precipitant, keeping the aqueous volume of the radioisotope mixture very low prior to its addition, and (b) the use of dry HC1 gas bubbled into either an aqueous solution or a mixture of ether and water. The first technique involves the use of a fairly stable reagent which can be kept for several days without discoloration0 The latter technique requires the use of dry HCl, a very nasty reagent, and an ice bath is necessary to remove the heat of solution of HClo Two modifications of each of these two techniques were evaluated: (1) 1.5 ml of aqueous solution containing tracers and carriers to. which ten ml of the 4:1 HCl1ether reagent was added, (2) three ml of aqueous solution containing tracers and carriers to which ten ml of the HC1:ether solution was added, (3) ten ml of aqueous solution containing tracers and carriers into which dry HC1 gas is bubbled until the solution is saturated, and (4) eight ml of aqueous solution containing tracers and carriers to which three ml ether is added and into which dry HC1 gas is bubbled until the solution is saturated. The concentration of chloride was determined by tit;rati ng -the HC1 with standard NaOH to the phenolphthalein end point. In the 105 ml H20 case using HC1:ether reagent, a concentration of 8,5 M was found compared to 7,5 M in the 3 ml H20 case. In the case of dry HC1, a 12 M solution resulted, and in the case of dry HC1 and ether, a molarity of 7.3 was found, The following procedures were used. 12

A. HCI - Ether Solution 1. Add ten mg of carrier and sufficient tracer of the contaminating ion (e.g., Sr, Ca or Co, Ru, etc.) to a clean 15 ml centrifuge cone and take necessary steps to secure exchange. 2. Add ten mg of barium carrier and make up to either 1-1/2 ml or 3 ml with water. (Also add barium tracer when determining barium yield.) 3. Add ten ml of HCl:ether solution containing four volumes of concentrated HC1 and one volume of ether. Stir thoroughly. 4. Digest for five minutes at room temperature with occasional stirring. 5. Centrifuge for five minutes at top speed. 6. Remove the supernate by slurping and prepare the precipitate for counting. B. Dry HC1 Gas 1. Add carriers and tracers as in A above. 2. Make up volume either to ten ml with water for procedure using plain dry HC1 or to eight ml and add three ml ether for the combination. 3. Immerse in ice batho 4. Bubble dry HC1 gas through the solution to saturation. This requires about one minute. (Note: When no ether is present, large bubbles of HC1 come to the surface at saturation, but in the presence of ether^ the saturated solution forms one phase from the aqueous and organic phases initially present.) 5. Digest the solution at room temperature for five minutes with occasional stirring. 6. Centrifuge at top speed for five minutes. 7. Remove the supernate by slurp`-t~ube and prepare the precipitate for counting. 13

The yield data obtained for these procedures are shown in Table IIIo The effect of the various contaminating elements (Table IV) was determined using the optimum conditions for low Sr and Ca contamination (3 ml H20), Oxalate Separations Precipitation of strontium and calcium as the oxalates is discussed thoroughly in standard works (26, 53), and it is a convenient way of quantitatively reducing these elements to a weighable and reproducible form, suitable for counting. Precipitation is complete only when the solution is heated and an excess of ammonia is present. The following procedure was used: 1. Add ten mg of carrier and sufficient tracer of the contaminating ion, e.g., Baor Co, Ru, etc,, to a clean 15 ml centrifuge cone and take necessary steps to secure exchange. 2. Add ten mg carrier of either strontium or calcium and stir thoroughly. Also add strontium and calcium tracers when determining their yield. 5. Dilute the solution to eight ml with water. 4o Add sufficient concentrated NH4OH to obtain an excess. One ml is usually satisfactory. 5. Heat to boiling and add two ml of a saturated solution of (NH4)2C204, and stir thoroughly. 60 Heat again to boiling and allow to stand for five minutes without applied heat, while stirring occasionally. 7. Centrifuge at top speed for five minuteso 8. Remove the supernate by slurp tube and prepare precipitate for counting. The results obtained by use of this procedure are shown in Table III, while the decontamination values for representative elements, when present at the point of separation, are presented in Table IV. 14

Sulfate Separation The precipitation of BaSO4 has been used generally for the separation of barium from simple solutions in a form suitable for weighing and counting. It is not a general decontamination step because of the difficulty in performing further operations on this highly insoluble substance. It is most useful, however, as a final step to secure a form which may readily be dried, weighed, and mounted for countingo The conditions for quantitative determination involve the slow addition of dilute sulfuric acid to the hot barium solution followed by a lengthy digestion period (53)o In more recent work, the sulfate ion is liberated by the'thermal decomposition of dimethyl sulfate thus accomplishing homogeneous precipitation (14). The following procedure was used in this work: 1. Add ten mg carrier and sufficient tracer of the contaminating ion e.g., Sr, Ca or Co, Ru, etc., to a clean 15 ml centrifuge cone and take necessary steps to secure exchange. 2. Add ten mg of barium carriero Also add barium tracer when determining barium yield. 3. Dilute to ten ml with one M HNO3 and stir thoroughly. 4, Add one ml 10% H2SQ4, stir thoroughly and digest at room temperature for five minutes with occasional stirring. 5. Centrifuge at top speed for five minutes. 6. Remove the supernate by slurp tube and prepare the precipitate for counting. The results obtained with this procedure for the alkaline earths are shown in Table III, and the decontamination results obtained with the carrier, and tracers of the contaminants are shown in Table IVo 15

DISCUSSION OF RESULTS Under the conditions prevalent in radiochemical separation procedures for activity derived from bombardment or fission, equilibrium conditions are seldom, if ever, obtainedo As a result, the conditions chosen for a given separation are compromises based on standard analytical methods, modified to give the maximum separation from the undesirable elements even at the cost of a lower yield of the desired constituent. The time required to perform the separation may also be a`determining factor in its choiceo Chromate The yields reported in Table III indicate the type of procedure required to secure a good separation of barium from strontium and calcium. As the pH of'this precipitation is raised from four to six the yield of barium rises from 70 to 86%, but the contamination due to strontium is raised from 1.6 to 22o. The calcium contamination is also increased from 0.8 to 1.7%, but the change is of little consequence due to the lack of reproducibility of the results. Thus, the optimum conditions chosen for the separation of barium from strontium are those at pH 4 in the acetic acid-sodium acetate buffered solution. Most of the elements such as Ce, Ire Zr, Sb, Se, Ru, Sn, and Ta that interfere with this precipitation are easily hydrolyzedo Some separation can be obtained from Ce, Zr, Ru, and Ta, however, due to the slow precipitation of their hydrous oxides under the conditions of separationo In the case of silver, the insolubility of the chromate accounts for the large interference. Antimony gives a large contamination due not only to hydrous oxide formation but also to the precipitation of basic salts in the weakly acid solution. Visual observation of conditions during and following precipitation indicate that Sb, Sn and Ta form precipitates upon addition of the buffer. In 16

the case of tin this is undoubtedly the hydrous oxide and antimony probably forms an oxy-chloride or nitrate, Latimer (40) mentions the insolubility of oxy-fluorides of tantalum, and this is probably the mechanism of its contaminationo A high degree of separation from diverse elements is not required for this method since its applicability is primarily in the separation of barium from strontium0 A higher degree of separation from elements easily hydrolized is best obtained by strong acid precipitations of members of the alkaline earth groups using reagents such as 80% HN03, concentrated HC1, or dilute H2S04. Nitrate The yield of barium and strontium is lowered as the concentration of HN03 is reduced from 80% to 60% and a better separation from calcium is obtained as this concentration is lowered, If high yields are desired and calcium is not present, 80% HN03 should be usedo If calcium is present, howevers, it would probably be worth the loss in yield to use 60% HN03 and secure more complete separation from the calciumo A coprecipitation with barium and strontium will carry a sizeable portion of calcium, if it is desired Calcium nitrate is soluble, however when present alone in any of these three concentrations of HN03 (68), Of the other elements studied, only antimony is a major interferenceo Visually, the antimony solution was cloudy at the end of centrifugation, indicating the presence of a slowly forming solid phase, probably the antimony acid. Two distinct layers of precipitate were visible at the tip of the centrifuge cone, substantiating this premiseo Hydrochloric Acid Use of the more complicated and hazardous procedures involving dry HC1 gas are not warranted by the results of these experiments given in Table III. In fact, observations indicate that precipitation in the three ml acid is slower than that on addition of dry HECl, thereby giving better decontamination as is shown in the case of strontiumo Calcium is not a significant 17

interference under any of the conditions used. The best separation of barium from strontium was obtained with ten ml HCl:ether reagent and three ml of aqueous solution containing the tracers and carriers. While the yield was 10% lower than by the procedure involving 1.5 ml of aqueous solution, in most cases this is not restrictive. Upon addition of the ether reagent there is formed a precipitate of silver chloride which is readily soluble in excess reagento While antimony is again the most prominent interference, the mechanism is not obvious. If antimony is not present, however, this method is fast and efficient, and it requires no precautions other than those normally required when handling ethero The results are generally better than those of nitrate precipitations, due to a lower viscosity of the supernate which allows more complete removal by vacuum. The precipitate of BaC12 o 2H20 is easily soluble in water, facilitating further separations. Oxalate For this precipitation, the yields of strontium and calcium are sufficiently high to make the oxalate step applicable to any overall alkaline earth separation procedure. It is not designed as a decontamination from barium, but barium is not completely carried by this procedure, and a separation may be made with careful control of conditions. This was pointed out by Hillebrand et al (26). The similarity between the crystaline forms of barium and strontium is undoubtedly the cause for the higher contamination by barium of the strontium precipitate even though the calcium oxalate is more flocculent Hydrous oxides, on the other hand, are carried to a larger extent on the more bulky calcium oxalate. For example, in the cases of Ce, Zr, Sb, and Sn, the addition of the ammonia causes immediate precipitation, and coagulation is accelerated by boiling, Iridium and ruthenium are complexed by the addition of ammonia, but the complex is destroyed by boiling and the oxide is precipitated. 18

The case of these two elements shows most clearly the flocculent character of the calcium oxalate since precipitation of the oxide occurs concurrently with that of the oxalateo For tantalum and cobalt, the coagulation of the oxide precipitate was visibly more rapid with strontium than with calcium. Solenium begins to precipitate upon heating the ammoniacal solution prior to addition of oxalate. Sulfate This method is completely unsatisfactory for the precipitation of strontium sulfate since some agent is required to lower its solubility and accelerate its coagulation. This is usually accomplished by the addition of alcohol and by heating the solution (14)o As the r-sults indicate, barium is completely precipitated under these conditions, while about half of the strontium and only 10% of the calcium is carried on the barium sulfate. Strontium sulfate is more completely precipitated in the presence of barium or calcium under these conditions than when these ions are not present. It if is necessary to work with a barium sulfate precipitate in the course of a separation, it may be dissolved by heating in an ammoniacal solution of versene (52). Upon dilution the barium sulfate again precipitates but some decontamination is accomplished. For example, in one case, 7.1% of the cerium present was carried on the initial barium sulfate precipitate. After dissolution of this precipitate, warming with versene, and reprecipitating by dilution and acidification, this contamination was lowered to about 1% of the original amount presento Acidification with concentrated acids will cause precipitation of the hydrogen versenate which lowers the decontamination. The precipitate of barium sulfate is highly compact, resulting in the small contamination of 0.5-0.6% for certain elementso Those ions carried to a larger extent are carried by other than purely mechanical meanso For example, Ag2SO4 is sparingly soluble in these solutions as are the oxy-sulfates of ions such as Zr(IV) and Sb(III). Also precipitation of a barium salt of the 19

sulfate complexes of zirconium may contribute to its contamination by analogy with the insolubility of the barium salt of the hexa-fluoride of zirconium. This may also cause the high cerium contamination. An insoluble barium chlor.-b iridate may be induced.toprecipitate accompanying.the barium sulfate,. a possible reason for its 5.4%..contamination of;the BaC2; 2H20 precipitation. SUMMARY: OPTIMUM PROCEDURES It is possible from the results of Table III and IV and the discussion of the previous section to synthesize optimum procedures for each of the three alkaline earth elements, barium, strontium and calcium. Barium The primary separation of barium and strontium from other elements would appear to be a precipitation of barium and strontium nitrates with 60% HN03 * This will give one 80 yield for barium and strontium and result in at least a 50-100 fold decrease in contaminants for each cycle. Separation of barium from strontium may be accomplished by either chromate precipitation at pH = 4 or by chloride precipitation in 7,5 M HC1 with ether prebent for a comparable separation. The amount of strontium in the precipitate is a factor of 50 below that present in the solution in each case. By use of the chromate method, a precipitate is obtained which is readily usable for counting, although the pH of precipitation may cause contamination by other elements. The chloride separation is performed in strong acid solution and decontamination is better for other elements. The yield of barium is around 80%. Final precipitation as the sulfate is the usual method for preparation of counting plates. Yields may also be obtained in this manner with fair accuracyo A sample procedure based on these separations is shown in Table Vo 20

Strontium Strontium may best be separated from other elements by first separating barium and strontium together as nitrates. Barium is then separated by chloride precipitation in 12 M HCl in as small a volume as is practicalo Over 90% of the strontium should remain in the supernate. This precipitation may be repeated to secure a better separation, the amount of barium being reduced by a factor of 100 by each cycle. The HC1 supernate solution containing the strontium is then evaporated or neutralized and the strontium separated as oxalate in basic solution. Scavenging steps may also be of value in these separations and are being investigated. Calcium Calcium may also be separated as the nitrate with strontium and barium in 80% HN03. The yield is about 70% per cycle. Barium and strontium are then removed by repeated sulfate precipitations in acid solutions. This sulfate separation will remove over 99% of the barium and 60% of the strontium while removing only 5-10% of the calcium per cycleo The supernate is then neutralized and the calcium separated as the oxalateo SUMMARY The yield and decontamination data presented in Tables III and IV can be used with a minimum of further development as a basis for specific procedures for separations of the alkaline earths to fit a particular problem. It is important to remember, however, that these rapid separations are made under nonequilibrium conditions and are reproducible only if the conditions of the separation are closely duplicated. Changing the order of addition of reagents, amounts of carriers, concentration of reagents, solution volumes or the size of equipment, may change significantly both the yields and decontaminationso 21

ACKNOWLEDGEMENTS This program was supported in part by the Atomic Energy Commission. 22

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FIGURE AND TABLE CAPTIONS Fig. 1. Periodic Table of the Elements. Figs. 2-8. Growth and Decay of Tracer Mixtures. 2. Ba140,La40o. 3 Ce144 prl44 3. Ce144Pr144 4. Ru06 10Rh 113 S113M 5. Snll3,Inll3m 6. Sr0,y90 7. Zr95,Nb95 covering 15 days. 8. ZR95,Nb95, covering 320 days. Curves: A. Total activity of an initially pure parent fraction. B. Activity due to parent. C. Decay of freshly isolated daughter fraction. D. Daughter activity growing in freshly purified parent fraction. Table I. Chemical Characteristics of Tracer Solutions. Table II. Nuclear Characteristics of Tracers. Table III. Summary of Yield Data of Precipitation Reactions for Barium, Strontium, and Calcium. Table IV. Contamination of Alkaline Earth Precipitates by Other Activities. Table V. Sample Procedure for the Separation of Barium from other Activities. 26

THE PERIODIC TABLE OF THE ELEMENTS H ____He Li Be B C N 0 F Ne Na Mg Al Si SP SCI A K Ca Sc Ti IV ICrMn FeCoNi Cu Zn GaGe AsSe BrKr Rb-Sr Y ZrNbMoTc Ru Rh Pd AgCd In Sn SbTe I Xe Cs Ba La sHf TaW Re Os Ir Pt Au Hg TI Pb Bi Po At Rn Fr ro AcEARTHS Fr LRaNTAc ID LANTH ANID elPr NdI Pm Sm Eu Gd Tb Dy Ho Er TmYb Lu RARE EAJThS P N Am Bk Cf E Fm ACTINIDETh U Pu Am Mv RARE EARTHS 7rnPa v'JiB J[Cm/ak jcf EJFm J

200 -I — 100 _ 0 Ba40- La140 12.8 DAY 40 HOUR 0 40 80 120 160 200 240 TIME (HOURS)

I I I I I I I 200 A 100 10. Ce 44 Pr144 280 DAY- 17 MINUTE 0 40 80 120 TIME (MINUTES)

200 I 00 _B. 1 100 0 10 106 D106 Ru Rh I YEAR -30 SECOND 1!!,I I I! I I I 0 30 60 90 120 150 180 TIME (SECONDS)

200 A 100 c O 10 Sn -In"3 112 DAYp-105MINUTE 0 200 400 60-0 TIME (MINUTES)

200- A 100 o 10 Sr90 Y90 20 YEAR — 61 HOUR I__ I,, I I,. I I,.I I. I I, I, 0 60 120 180 240 300 360 TIME (HOURS)

200 oo>-.A BI 100 F-'0 I < 10= 0 Zr95-Nb95 65 DAY — 37 DAY 0 60 120 180 240 300 360 TIME (HOURS)

200 100 10 Zr95- Nb95 65 DAY -37 DAY 0 80 160 240 320 TIME (DAYS)

TABLE I CHEMICAL CHARAC'ERISTICS OF TRACER SOLUTIONS Received from Diluted Loss from Hydrol For Carrier-Tracer Isotope ORNL* as: with or Absorption Exchange 1. Ag-O10 AgNO3 in HNOs soln. 3M HNO3 large loss by abs. on glass thorough mixing from dil, acid soln. of tro Highly acid soln. of tro in borosilicate glass, no loss 2. Ba-140 BaCl2 in 0.8 M OolM HC1 none thorough mixing La-140 HC1 soln. 3. Ca-45 CaCl1 in HC1 solno O.1M HC1 none thorough mixing 4. Ce-144 CeC13 in HC1 soln. 3M HC1 none thorough mixing Pr-144 5. Co-60 CoC12 in HC1 solno 1M HC1 none thorough mixing 6. Cr-51 CrC13 in HC1 solno 1M HC1 none thorough mixing with Cr(III) 7. Cs-134 CsCI in HC1 solno OolM HC1 none thorough mixing 8. 1-131 NaI in NaOH, NaHSO3 0.1M NaOH none thorough mixing soln 9o Ir-192 IrCle in HC1 soln. OolM HC1 none thorough mixing, carrier also in HC1 before mixing 10. Ru-106 RuCl3 in HC1 solno dil, HC1 none thorough mixing of tracer plus Rh-106 Ru(III) in HC1

TABLE I (cont.) Received from Diluted Loss from Hydrol. For Carrier-Tracer Isotope ORNL* as: with or Absorption Exchange 11. Se-75 SeC14 in HC1 solh. 1M HC1 none thorough mixing 12. Sb-124 SbC13 in 3.3M HC1 3M HC1 none Sb(III) plus tracer, oxid. to soln. Sb(V) with Br2: red. to Sb(IiI) with hydrazine 13. Sn-113 SnC12 in HC1 soln. 5% HC1 none SnC12 in 5% HC1 plus tracer In-113 oxid. in excess NaC10. 14. Sr-89 SrCl2 in HC1 soln. dil. HC1 none thorough mixing 15. Sr-90 SrCl2 in HC1 soln. none thorough mixing Y-90 16. Ta-182 KTaO3 in KOH KOH soln. after standing, the original dissolution of carrier in HC1 ORNL soln. showed tan ppt. and Hf with warming in prescontaining the Ta-182 ence of tracer 17. Zr-95 complex in oxalic dil. oxa- none addition of Hf and separation acid lic acid as BaZrFo Nb-95 *All radioisotopes used in this work were obtained from the Isotopes Control Department of the Oak Ridge National Laboratories.

TABLE II NUCLEAR CHARACTERISTICS OF TRACERS (B) Spec. Act. Isotope Half Life Primary Radiations Daughter Counting 3B~~~~ yr~~ ~ ~Orig. Soln. 7 1. Ag-11O 270 days 0.087 (58%) Cd-llO (stable) 55.5 mc/gm scint. well 0.530 (35%) 2.12 (3%) 2.86 ( 3%) 2. Ba-140 12.80 days 1.022 (60%) 0.162 La-140 (40.0 hr) C.F. GM- 1.4 mg/cm2 0.480 (30%) 0.304 counter 0.537 La-140 40.0 hr 1.32 (70%) 0.49 (22%) Ce-140 (stable) 1.64 (20%) o.82 (16%) 2.26 (10) 1.62 (56%) 3. Ca-45 152 days 0.254 (100%) (none) Sc-45 (stable) 27.65 mc/gm GM- 1.4 mg/cm2 window 4. Ce-144 275 days 0.3 (70%) Pr-144 C.F. scint. well 0.17 (30%) Pr-144 17 min 2.97 (98%) Nd-144 (stable) 5. Co-60 5.27 yr 0.306 (100) 1 (0) Ni-60 (stable) scint. wel 1.17 V-51 (stable) 831 mc/gm scint. well 6. Cr-51 -2'7.8 days EC -92% EC - 8 0.32 (8%) 7. Cs-134 2.3 yr 0.079 (21%) 0.601 B-134 scint. well 0.255 ( 6%) 0.794 0.640 (54%) 0.570 (-50%) 0.676 (19%) 1.35 ( 3%) others weak..~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~I

TABLE II (cont.) Spec. Act. Isotope Half Life Primary Radiations Daughter O o Counting Orig. SoLn., Y 8. 1-131 8.0 days 0.595 0.363 Xe-131 (stable) C.F. scint. well 0.315 0.638 0,283. o8o 9. Ir-192 74.37 days 0.67 0.137 Pt-192 (stable) 4517 mc/gm scint. well 0.208 0.296 0.308 0.317 to 0.615 10. Ru-106 1 yr 0.0392 (100%) Rh-106 C.F. scint. well Rh-106 30 sec 3.53 ( 68%) 0.513 (23%) Pd-106 (stable) 3.1 ( 11%) 0.624;(12%) 2.44 (.12%) 11. Se-75 127 days 0.10 As-75 (stable) 49.5 mc/gm scint. well 0.12 0.14 0.26 0.40 12. Sb-124 60 days 2.29 (21%) 0.121 Te-124 (stable) 1142 mc/gm scint. well 1.69 ( 7%) 0.607 (95%) 0.95 ( 7%) 0.653 ( 5%) 0.68 ( 26%) 0.730 (24%) 0.50 ( 39%) 1.708 (70%) 2.04 ( 6%) 13. Sn-113 112 days EC-0.393 (100%) In-113m 15.79 mc/gm scint. well In-113m 105 min In-113 (stable)

TABLE II (cont.) Primary Radiations Speco Act. Isotope Half Life Daughter Counting B Z Orig. Solno 14o Sr-89 54 day 1o50 Y-89 (stable) C.Fo scint. well 15 Sr-90 199 yr 0o61 (100%) Y-90 C.F. GM Tube 1.4 mg/cm2 Y-90 61 hr 21l8 (100o) Zr-90 (stable) scint. well 16. Ta-182 111 days 0.53 1.2 W-182 (table) 409 mc/gm scint. well 1ol 1ol 0.05-1.0 17. Zr-95 65 days 0.571 ( 99%) 0.721 ( 99%) Nb-95 C.F, scint. well Nb-95- 35 days 0.16 (100o) 0.745 (100%) Mo-95 (stable)

TABLE III SUMMARY OF YIELD DATA OF PRECIPITATION REACTIONS FOR BARIUM, STRONTIUM AND CALCIUM* Precipitating Percent Carried Condition Calcium on Solution Barium Strontium Calcium on Barium Strontium Ammonium pH 4 70 + 3.4 1.6 + 0.3 0.8 + 0.08 Dichromate pH 5 73 + 4.0 8 + 0.2 1.1 + 0.08 pH 6 86 + 1.3 22 + 2.0 1.7 + 0.22 Nitric Acid 80% 100 + 5.3 100 + 1.7 27 + 2.2 51 + 3.2 70% 100 + 3.6 98 +1.4 2.4+0.3 11 +2.3 60% 86 + 3.3 81 + 4.2 0.9 + 0.05 2.6 + 1.0 Hydrochloric 3 ml H20 82 + 1.1 2.8 + 0.9 0.6 + 0.4 Acid 1.5 ml 20 92 + 2.2 11 + 0.7 0.8 + o.08 dry HC1 99 + 0.4 7.3 + 1.6 1.0 + 0.1 Ether:dry HC1 93 + 2.4 6.0 + 3 1.5 + 0.1 Ammonium 95% 59 on SrC204 Oxalate < 90 100 15 on CaC204 Sulfuric Acid xs Sulfate 100 57 on Barium 10 3.6 very slight alone *All values are average of quadruplicate runs. Errors are "standard deviations".

TABLE IV CONTAMINATION OF ALKALINE EARTH PRECIPITATES BY OTHER ACTIVITIES* pH 4 Precipitating Solution,, Perzent Carried.I A y Element P0%0 Nitric 60 Nitric Hydrochloric Oxalate Ions resent Chromate Acid Acid Acid on SrC24 on CaC2 Sulfate in Precipitating Solution Antimony 55 47 30 28 44 46 28 NO 3 C1 Barium 70 100 86 82 59 15 100 NO3, C1 Calcium 0.8 51 on Sr 2.6 on Sr 0.6 100 10 NOs3 Cl 27 on Ba 0.9 on Ba Cerium 6 5.2 2.5 0.9 98 95 7.1 NOs3, Cl Cesium 3.5 1 2 1.0 0.8 1.6 2.9 N03, Cl Chromium 1.2 1.8 1.0 0.7 89 96 0.5 NO3 Cl Cobalt 1.1 3 3.5 1 52 21 0.5 NO;, C1 Iodine 20.1.2 o.8 0.9 2.3 5.0 1.5 NO3 Iridium 27 4.2 0.9 5.4 47 68 11 NO0, CL Ruthenium 5 1.5 2.4 2 23 38 0.6 NO;, Cl Selenium 5.7 1.4 1.3 0.9 21 23 1.2 NO3, Cl Silver 89 1.91.5 0.8 1.2 2 14 NO3 Strontium 1.6 100 81 2.8 790 -- 57 NOs, Cl Tantalum 10 1 0.7 0.5 )49 24- 0. N03, Cl F Tin 99.5 11.2 0.8 73 95 0.5 NO03 C1 Zirconium 6.3 2.6 3.3 2 93 88 20 NO3, (F )? *Values are average of duplicates on barium precipitates except where noted,

TABLE V HC1:Ether Precipitation of BaC122H20 Yield 82% 1. Add carriers to 15 ml cone, Decontamination Factors secure isotopic exchange. 2. Ppt. BaC12'~ 2H20 from 3 ml 1-10 Sb aq vol by addition of 10 ml 10-100 Ir, Ru, Zr, Sr 4:1 HCl:Ether soln. 100-1000 Ca, Ce, Cs, Cr, 30 Digest 5 min,:room temp, Co, Ag, Ta, Sn, centrifuge 5 min, remove Se, I supernate HCl:Ether Precipitation of BaCl22H20 Yield 67% 4o Dissolve ppt, add carriers. Decontamination Factors 5. Ppt as in step (2) above. 6. Digest 5 min, centrifuge 10'100 Sb 5 min, remove supernate. l02-103 Ir, Sr 103-104 Ru Zr, 104-105 Ca Ce, Cs, Cr, Co,, Ag, Ta, Sn, Se, I HCl:Ether Precipitation of BaC122H2O Yield 55% 7. Dissolve ppt, add carriers. Decontamination Factors 8. Precipitate as in step (2)0 9. Digest 5 minm centrifuge 5 10-100 Sb min, remove supernate. 10 l104 Ir 104-105 Sr 105-107 Ca, Ce, Cs, Cr, Co, Ru, Ag, Ta, Sn, Zr, Se, I H2S04 Precipitation of BAS04 Yield 55% 10 Dissolve ppt, add carriers. Decontamination Factors 11o Make volume to 10 ml with 1 M HN03, ppt BaS04 by addi- 102-103 Sb tion of l:,ml 10% H2S04, 104-105 Sr, Ir 12. Digest 5 min, centrifuge 5 106-i08 Ca, Ce, Cs, Ru, min. remove supernate. Ag, Zr 10 -10 Cr, Co, Ta, Sn, Se, I Determination of Yield and Counting