- --------" U . S. Department of Commerce Research Paper RP1767 National Bureau of Standards Volume 38, February 1947 Part of the Journal of Research of the National Bureau of Standards Concentration of Isotopes of Chlorine by the Counter­ current Electromigration Method 1 By Samuel 1. Madorsky and Sidney Straus The isotopc 35Cl \"as co ncent ratcd in thc anode compartment of an elccLromi gratioJ) cell , with NaCl as thc electrolytc. The operation \\"as regulated by means of a stationary boundary bctwccn s o lu t ion ~ of NaOH and NaCl as the lower and uppcr liquids, respcc­ tively. A co ncen tration of 35C I from t hc normal valuc of 75. 76 pcrcent to a maximum value of 80_7 percent was obtaincd in 474 hours. The maximum initial scparation coeffi cicn t, <- I , ,,-as 0.207 X 10- 2_ 1. Introduction isotopic ratio is maintained in the. cathode com­ partment. Howevcr , if the chloride ion is allowed Kenda]] and Crittenden [1] 2 attempted to to react at the anode to form chlorine ga , it will separate the isotop ::lS of chlorine by the ionic­ esca pe. This r :.;action wa s prevented by inter­ migration method. They transported chlorine ions posing a solution of sodium hydroxide around the ina tube filled with agar-agar through a distance anode to form a boundary betwcen the chloride of 100 feet by means of a moving bouldary. An and hydroxide solutions. atornic-weigl1t determination of chlorine in the Sodium chloride in the 1'a tio N aCl :H20 = 1 : 30 forward sec tion of the gel failed to det ect any was used as the electrolyte. As the transport chrmge in the isotope ratio. MOL recently, a numbers of Na+ and Cl- are approximately 0.40 new method [2] based on the principle of counter­ and 0.60, respectively, the anode 1'e tituent was CUlTent electJ'omigration, has been developed at 1:18 NaOH, wh ereas the cathode restituent was the National Bureau of Standards for the separa­ 1: 12 HCl. Characteristic properties of the solu­ tion of isotopes_ The successful appli cation of tions employed are shown in table 1. As seen this method to the concentration of 39K and from this table, 1: 18 N aOH has a greater density HK [3} from solutions of K 2S04 and KCl suggested than 1 :30 NaCl, and, therefore, the alkali solution the possibility of concentrating the isotopes of should be the lower layer, and the salt solution chlorine by this method. The prcsent paper should be the upper layer at the anode boundary. describes som e experiments designed to conccn­ Such an arrangment is shown in the gooseneck­ tmte 35Cl from a solution of NaCl. shaped anode compartment in figure 1. II. Outline of Problem T ARLE 1.--Sollltions employed in the chlol'ine electro­ mi gration ex periments Chlorine appears in nature as a mixtlll'e of 75.4 percent 35Cl and 24.6 percent 3i Cl [4]. III an Ratio C0nrrn­ Dcnsity Solute sol ute- il,O tratioll at 25° C Normality electrom:igmtion cell 35Cl- can be conccntrated in the anode compartment, provided the original Percent Nael ___________________ _ 1: 30 9_ i6 1. 067 1. 782 NaOil _________________ _ I This paper wi ll appcar i l1 volume 6, divisio:l III, of tbe Manhattan I: 18 lO. 98 1.11 8 3, 067 Projec t Technical Scries _ n eL ___________________ _ 1: 12 14 _43 1.068 4_225 ' Figures in bracket indicate the literatm e references at the end of th is paper. Isotopes of Chlorine 185 were No. 40 bead frits. At the anode end the frit was held in place by means of a sealed-in glass cross, and at the cathode end it was supported by means of a screw and a glass rod passing through a rubber stopper . In experiments 2 and 3, frits similar to those at the ends of the packed column were also placed in the packing at intervals of about 3 em in order to impart greater rigidity to the compressed sand. The wall thickness of the packed tube was 1 mm. The electrode sections were supplied with manually controlled droppers, siphons, and manually controlled overflow cups (A and B, fig. 1). The cathode was of the flushed type receiving 1: 30 N aCl solution in addition to a stoichiometric amount of 1: 12 HCl. The elec­ trodes were made of platinum gauze, about 4 FIGURE I.- Diagram of electro migration cell 11sed in the cm 2 in area. chlorine ex periments. The boundary was maintained between 1: 30 III. Apparatus and Experimental N aCI and 1 : 18 N aOH as the upper and lower Procedure liquids, respectively, in an annular space, K , be­ tween the outer tube and t he inside cooler, as The apparatus is shown diagrammatically m shown in figure 1. The boundary ring had an in­ figure 1 and photographically in figure 2. The side diameter of 13 mm, was 1.5 mm wide, and packing was 2 cm in diameter and 10 cm long. It had a total area of 0.6 cm 2• The anode volume, consisted of No. 107 ballotini glass beads in i. e., the volume of liquid between the boundary experiment 1 and of 60- to 100-mesh Ottawa sand and the packing, was about 10 ml. The boundary is shown in figure 3. Pertinent data of all the III the other experiments. The packing supports experiments are shown in table 2. T A BLE 2.-E:LpeTime7ltal details and r es ull .~ E xperiment P oten· Anode I I nil;'1 No. Packing tisl volume (E- J) X IO ' ---------------- (tm p rnl 1 ____________ l oo-mesh ballotini glass heads, 0.430 10.4 0. 115 with DO inte rm cdi ~ te fr its. 2 ____________ . 60· to loo-mesh sand , 3 inter- .430 10 . 4 . 128 Il" cdhte frits. 3 .. ________________ do _____________________ ___ _ .430 11.0 . 180 4 ___________ ._ 60- to 100·mesh sand, no inter- . 500 II. 0 .207 mediate frits. 5 _____________ . ____ do _______________________ __ .500 I 11. 0 I . 183 In filling the cell, 1: 18 NaOH sohltion was first poured into the anode compartment to the level where th e boundary was expected. Sodium chlor- C ide solution (1: 30) was then poured into the cathode compartmen t and allowed to seep through the packing into the anode volume space E (fig. 1). Further additions of N aOH solution kept the junction between the two liquids in the neighbor­ hood where the boundary was desired. After the FIGURE 2.- ElectTomigration cell assembly showing dropper cell was filled to the proper levels, the current and con stant level devi ces. was turned on and the addition of restituents 186 Journal of Research order to control the acid rate 'moro closely, it was first fod into a constant overflow cup, G (fig. 1), and from there into tbe cathod compartmen t H through manually controlled droppel's. The cells operated bost when the cathode overflow from B was slightly acid, as was indicated by methyl red introduced with the Hel restituent. The stoichiomctric amounts of H e l ancl NaOH solutions required pCI' ampere hour arc 9.4276 and 13.5902 g, respectively. Thc actual amount of Hel added was slightly in excess of that ]'oq uired theoretically. For N aOH an excess of about 20 g per ampere hour was used. This excess wa by­ passed through a siphon, as shown in fi gure l. The amount of cathode flu shing restituen t, N ael, added was 24 g pel' ampere hour. The cells under normal operation ran slightly alkaline above the boundary and thl'ough .the paeking column, as was indicated by methyl rod fed in Lo the anode with the NaOH rostituen t. As a chock on the operation of tho colIs, analy e of the anode and cathode ovorflow liquids, as well a of samples drawn from various parts of the colI , woro made at intervals. Overflow liquid from A (fig. 1) and samples drawn from D wer e analyzed for N aOH. Overflow liquid from B was analyzed for N ael and H e l, and samples drawn from 0 FIGURE 3. - Details of cathode compartment. wero analyzed for N ael and N aOH. No chlorine A. Boundary. was fOlmd either in eup D or in the anode overflow TABLE 3.-Analysis of cell and overflow liquids in ex peri­ started. A sharp boundary appeared witbin a ments 2 and 3 few minutes. The CUlTen t in all the experiments was about Hours Ovel'­ Liquid Ovcrflow rrom B I Liquid in CLIP C 0.5 amp and the voltage between the electrodes ariel' fl ow frol11 siari from A, CLI P .0, about 80 . NaOHNaO Il Na~-I-~ I NaCl-r ~a ou- The oprration was con tinuous, requiring li ttle EXPERI ME N'J' 2 attention. In the daytime, drop rates were ad­ j usted two to three times, whil e during nights the % % % % % % cells were left without attention. Fluctuations of 10.95 10. 95 9. 76 0 9.76 0 the boundary level during off-duty periods were 65 10.15 9. 93 . 21 10.87 .24 137 9.34 10.58 _.------ -- .. --_.- --- ----------- ----- --- generally within 1 em, but occasionally it would 209 10. 24 10. 02 .40 .10. 91 .23 305 lO .30 JO. 05 .30 10.86 .22 r each a maximum of 2 cm. As the cross section 411 10. 09 9.94 .