Separation of Silver from Cobalt and Nickel by Ion Exchange Chromatography R. P. BHATNAGER and R. P. SHUKLA Deparfmenf o f Chemistry, Holkar College, Indore, India
b Ion exchange chromatographic methods for the separation of silver from cobalt and nickel were studied with a view to utilizing them in the recovery of silver from nickel and cobalt ores. Separations were tried on Amberlite IR-120 in the hydrogen and sodium forms using nitric, citric, and tartaric acids, and sodium nitrate and nitrite as eluting agents. The separation of silver from cobalt by complexing cobalt as cobaltinitrite [nitrocobaltate(lll)] was also attempted. Elution with a 2% solution of sodium nitrite successfully separated silver from cobalt as well as from nickel. The utility of the separation was shown by a modified Volhard method for the determination of silver in the presence of Cof2 and Ni+2.
quick-fit joint (B-19) to an adapter to collect the fractions. Three reservoir bottles (for influent, regenerant, and distilled water, respectively) were used to store the liquids and they were connected with the column through T-joints and three-way stopcocks to keep the process continuous.
S
In the first attempts to elute silver without eluting cobalt the resin was used in the hydrogen form. The column was packed by adding resin in a water slurry to a depth of 20 cm. (total capacity 20.3 meq.). -4 20-nil. solution consisting of a mixture of cobalt nitrate and silver nitrate (10 ml. of 0.1N silver nitrate and 10 ml. of 0.1N cobalt nitrate) was passed through the column a t a flow rate of 5 ml. per sq. cm. per minute. Dilute hydrochloric acid and l-nitroso2-naphthol spot techniques were used to test for the presence of Ag+ and Coz+ ions. Both were retained completely by the column. The column was washed and then eluted with 6% nitric acid solution. The silver was obtained in 12 fractions of 20 ml. each, but all the fractions contained cobalt. These studies were repeated using 5 7 tartaric acid and also 5% citric acid as eluents but elution was unsatisfactory. Further studies were tried using the resin in the sodium form. A 575 sodium nitrate solution was used as eluting agent. The silver was completely eluted in 19 fractions of 20 ml. each; hon-ever, each fraction contained cobalt although in minute amounts. The use of the citrate form of the anion exchanger Amberlite IRA-410 to trap cobalt was also unsuccessful. Saniuelson and Sachhrani (7) have suggested the possibility that cobalt and nickel ions were trapped by this form of anion exchanger, but our studies did not confirm this.
REAGENTS
Cobalt and nickel solutions were prepared from their nitrates (hexahydrates) of British Drug House AnalaR quality, while silver solutions were prepared from the nitrates of Johnson of Hendon Ltd. (London). All other eluting agents used were of British Drug House AnalaR quality. The resin used was Amberlite IR120 (analytical reagent quality, Rohm &- Haas Co., Philadelphia, Pa.) PROCEDURE
when it occurs in ores and alloys with cobalt or nickel, requires lengthy precipitation methods for its separation. The use of ion exchange chromatography for the separation of silver from cobalt and nickel could effect a complete separation of this costly metal by a less time-consuming and more efficient method (particularly n hen small amounts are present). Attempts have been made in this direction in the present studies. Several procedures have used ion exchange techniques for the selective exchange of cobalt ( 3 ) or its separation from nickel and copper (1,2,4). In the latter methods, nickel and cobalt were separated from each other or from other elements such as copper, manganese, or zinc chiefly by using hydrochloric acid solutions of differing strength as the eluting agent. The use of hydrochloric acid, however, is undesirable when silver is present in solution nith either cobalt or nickel. Consequently, nitric acid, sodium nitrate, and other eluting agents were tried for the separation of silver from cobalt and nickel. ILVER,
APPARATUS
-4glass column (50 em. X 1.0 cm.), provided with a removable perforated porcelain disk just above the lorn-er end, was used. A glass wool pad was placed over this disk and the lower end of the column was fitted n-ith a
Further studies rvere made using the resin Amberlite IR-120 in the sodium form and 2% sodium nitrite as eluent. The first nine fractions of 20 ml. each contained all the silver in them and no trace of cobalt. This separation appeared to be satisfactory and quantitative. Similar studies using mixtures of silver and nickel solutions on Amberlite IR-120 ( S a + ) and 2% sodium nitrite as eluting agent were also successful. The separation of cobalt as complexed sodium cobaltinitrite was also tried. Cobalt in a mixture of silver and cobalt nitrates was converted to sodium cohaltinitrite by adding 5 ml. of glacial acetic acid and the required amount of sodium nitrite. Cobalt was oxidized by using 5 ml. of 20-volume hydrogen peroxide The solution was stirred nTell and exposed to the air for about 10 minutes until the color changed to yellow (showing the formation of the complex). A spot test to determine if cobalt were present in the solution was negative, which indicated that cobalt was present in the complexed anion. This solution was then used as influent. The resin was used in the sodium form. (The hydrogen form was not used, as it decomposed the complex.) Cobalt as complexed anion was not exchanged; while the silver was retained by the column. This silver was then eluted with 5% sodium nitrate and i t contained only traces of cobalt (probably due to slight decomposition by the resin). Detailed Studies with 2y0 Sodium Nitrite as Eluting Agent. EFFECTOF FLOW RATE. The effect of flow rates using the procedure described above was studied. Flow rates of 1 nil. per sq. em. per minute and 3 ml. per sq. em. per minute were unsuitable, as the last fractions of silver showed the presence of traces of cobalt. A flow rate of 5 ml. per sq. cm.-l per min.-' was satisfactory and showed no presence of cobalt in the last fraction of silver effluent. A flow rate of 8 ml. sq. cm.-I per niin.-' was equally successful and was better in cases where the per cent of silver in the mixture was small. ~ helped to effect a Thus a faster f l o rate clear separation. EFFECT OF CONCEKTRATION OF SILVER. The separation studies were repeated with the solutions containing the two ions concerned in varying proportions. The silver was eluted VOL. 32,
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with 2% sodium nitrite solution in all cases. Clear and quantitative separations were possible with 75, 50, 33.33, and 16.67% silver in the mixtures with cobalt. After silver elution cobalt could be completely eluted with 200 to 350 ml. of 5% sodium nitrate solution. SEPARATION OF SILVER FROM NICKEL. Similar studies with silver and nickel mixtures were repeated. Sodium nitrite (2%) was used as the eluting agent. It was possible to separate silver completely by a similar procedure from mixtures containing 75, 50, 25, and 10% silver with nickel as nitrates. Only in the last mixture, which contained 90% nickel, the last fraction (6th 20-ml. fraction) contained traces of nickel. Nickel in all cases could be eluted later by the same eluent (200 to 350 ml.). MODIFICATION OF VOLHARD METHOD. I n all the above methods a rapid volumetric method such as the Volhard method was needed for the estimation of silver. The elution by sodium nitrite caused difficulty in the estimation because the indicator, ferric nitrate, failed in presence of the nitrite ion in the solution. Hence a process similar to one given below was employed. The solution containing silver ion in the presence of excess nitrite ion (forming probably the complex ion [Ag (NO&]-) was acidified with a few milliliters of dilute acetic acid. About 1 gram of urea was then added to it and the solution boiled to destroy free nitrous acid so formed. The solution was then cooled and acidified with dilute nitric acid until the effervescence (which was started by its addition) ceased. The solution was boiled for a
few minutes more, cooled, and titrated with ammonium thiocyanate solution using ferric nitrate as indicator. The precipitation of silver thiocyanate was satisfactory and the appearance of end point was sharp. If this procedure is not used, the titer continues to decompose. At the same time, ferric indicator changes to the ferrous state and hence does not give the end point. This procedure was also used for silver titrations in the presence of the colored ions of cobalt and nickel after their removal by the ion exchange technique detailed above. The percentage error in all the cases was less than *0.5. DISCUSSION
Detailed studies with 2% sodium nitrite as eluting agent indicated the quantitative separation of silver from cobalt as well as from nickel with a fast flow rate of 8 ml. per sq. em. per minute 011 Amberlite IR-120 (Na+) in all cases. The use of sodium nitrite as an eluting agent for silver a t first appeared to be unusual. But it was possible, probably because of the formation of the complex ion [Ag(NO&]- whose formation has been suggested by Abegg from electrometric studies as cited by Remy (6) and also by Nardelli, Cavalca, and Brailanti (6). I n an excess of sodium nitrite silver nitrite remains as a soluble complex and hence the eluted silver remains in the effluent solution. It can easily be titrated by the modified Volhard method as described. The use of a complex formation for the separation of cobalt from silver before
the sorption step was also successful. Cobalt as the complex, nitrocobaltate (111) ion, was not retained by the cation exchanger and hence separated. Although the process was effective, it was not quantitative, as separated cobalt as well as silver solutions were contaminated with traces of impurities. The applicability of such a separation as a modification of Volhard’s method for estimating silver volumetrically was equally successful. Standard books on quantitative analysis suggest that the presence of colored ions (as cobalt and nickel) interfere with the Volhard method. The present studies show that the method can be used, after the separation of ions of cobalt and nickel by ion exchange chromatography, to obtain the desired accuracy. LITERATURE CITED
(1) Atteberry, R. W., Larson, Q. V., Boyd, G. E., Abstracts, 118th Meeting,
ACS, p. 8G, Chicago, Ill., September 1950. ( 2 ) Blasius, E., Kegwer, N., Naturwissenschaften 39,257 (1952).
(3) Jentzsch, Doe, Chem. Tech. (Berlin) 6. (1954). - ,339 --.- - ~ (4) Kraus, K. ’A.,Moore, G. E., J. Am. Chem. SOC.75, 1460 (1953). ( 5 ) Nardelli, M., Cavalca, L., Brailanti, A.. Gazz. chim. ital. 82,413 (1952). (6) Remy, H;, “Treatise on Inorganic Chemistry, Vol. 11, p. 440, Elsevier, New York, 1956. ( 7 ) Samuelson, O., Sachhram, K., unpublished (cited in “Ion Exchangers in Analytical Chemistry,” p. 156, Wiley, New York, 1953). RECEIVED for review November 10, 1959. Accepted February 12, 1960.
Pa per Chromatog ra phy of Bis phe no1 A G. CHALLA and P. H. HERMANS Institute for Cellulose Research, Achter St. Piefer 6B,Utrecht, Netherlands
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b 2,2 Bis(4 -hydroxy phenyl) p r o p a ne and three principal impurities occurring in commercial bisphenol A have been separated by paper chromatography in an atmosphere of ammonia using a mixture of 1 -propanol and kerosine as eluent. In the case of fairly pure samples the impurities are preconcentrated by fractional vacuum sublimation. On commercial bisphenol A samples, the method gives purity data which agree with freezing point depression values.
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recent article, Anderson, Carter, and Landua (1) described a paper chromatographic method for the quanN A
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ANALYTICAL CHEMISTRY
titative analysis of commercial grades Some years ago the authors developed of bisphenol A. The main constituent, a method primarily intended for qualitap,p’-BPA [2,2-bis(4-hydroxyphenyl)pro- tive and semiquantitative analysis of pane], and the principal impurities, bisphenol -4. It involved simple oneo,p‘-BPA [2-(2-hydroxyphenyl)-2-(4 dimensional paper chromatography and, hydroxyphenyl) propane], codimer [4, when necessary, preconcentration of 4‘ - hydroxyphenyl - 2,2,4 - trimethylthe impurities by vacuum sublimation. chroman], and BPX [2,4-bis(a,a-diThe authors’ procedure appears to niethyl-4-hydroxybenzyl)phenol], Lvere have advantages over that of Anderseparated on two one-dimensional paper son, Carter, and Landua because of its chromatograms using as eluents water simplicity and because it is also easily and carbon tetrachloride, respectively. adaptable to quantitative work. Preconcentration of the impurities in the mother liquor from a recrystallizaEXPERIMENTAL tion of bisphenol A was necessary, when the amounts of the impurities in Paper Chromatography. From B the original sample were less than 1%. micropipet 5 p l . of 5% solutions in
