Extraction of copper (II) from diluted hydrochloric, nitric
and sulphuric acid solutions with monooctyl a-anilinobenzylphosphonate
(MOABP) dissolved in chloroform, has been studied.
Copper is quantitatively extracted from the solutions at 4.5 ·< < pH < 6.2. Although zinc is also extracted from diluted mineral
acids, the separation of zinc from a large amount of copper is
feasible in the presence of cyanide.
Copper (II) and MOABP form a stable yellow colored complex,
whose solution in chloroform follows the Lambert-Beer\u27s law. A
procedure for rapid spectrophotometric determination of copper
has been developed. The influence of various cations and anions
on the absorbance of the complex has been investigated.
The ratio of copper to MOABP · in the extractable complex
has been established spectrophotometrically, and from the dependence
of the copper distribution ratio on the MOABP concentration
in the organic phase. A MOABP complex having 2 ligand molecules coordinated to the copper ion has been isolated in pure form

B. Tamhina

M. J. Herak

V. Jagodić

English

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CROATICA CHEMICA ACTA CCACAA 45 (4) 593-601 (1973) CCA-806 YU ISSN 0011-1643 543. 7 ;545.82 Original Scientific Paper Solvent Extraction and Separation of Zinc from Copper and Direct Spectrophotometric Determination of Copper (II) by Monooctyl a -Anilinobenzylphosphonate B. Tamhina, M. J . Herak, and V. Jagodic Laboratory of Analytical Chemistry, Faculty of Science, University of Zagreb, and Institute »Ruder Boskovic«, 41000 Zagreb, Croatia, Yugoslavia Received October 8, 1973 Extraction of copper (II) from diluted hydrochloric, nitric and sulphuric acid solutions with monooctyl a-anilinobenzylpho-sphonate (MOABP) dissolved in chloroform, has been studied. Copper is quantitatively extracted from the solutions at 4.5·< < pH < 6.2. Although zinc is also extracted from diluted mineral acids, the separation of zinc from a large amount of copper is feasible in the presence of cyanide. Copper (II) and MOABP form a stable yellow colored complex, whose solution in chloroform follows the Lambert-Beer's law. A procedure for rapid spectrophotometric determination of copper has been developed. The influence of various cations and anions on the absorbance of the complex has been investigated. The ratio of copper to MOABP · in the extractable complex has been established spectrophotometrically, and from the depen-dence of the copper distribution ratio on the MOABP concentration in the organic phase. A MOABP complex having 2 ligand molecules coordinated to the copper ion has been isolated in pure form. INTRODUCTION Monooctyl a-anilinobezylphosphonate (MOABP) has been utilized as a suitable reagent for extraction and separation of certain metals. 1- 9 Physical properties of MOABP and its extraction efficiency in different solvents have also been studied.10•11 This paper descri!bes the use of MOABP as an extractant to separate zinc from a large amount of copper. Since 65Zn is produced in a cyclotron by nuclear reaction 65Cu(d, 2n)65Zn, this separation has a prac-tical importance because it yields radiochemically pure zinc. Although both zinc and copper are extracted under similar conditions, their separation was achieved with the aid of an alkali cyanide. It has been found that MOABP forms stable colored complexes with some metals. This property has been utilized to determine metal extractable species.1•8 Copper(II) forms a yellow complex with MOABP whose solution in chloroform follows the Lambert-Beer's law. On the basis of this property a new spectrophotometric determination of copper was developed. The expe·· rimental conditions for quantitative extraction of copper and its subsequent determination in the organic phase are described. The influence of various cations and anions on the absorbance of the copper-MOABP complex was investigated. The composition of the extractable copper complex was studied 594 B. TAMHINA ET AL. spectrophotometrically and was also established from the dependence of copper distribution ratio, D , on the MOABP concentration in the organic phase. A copper-MOABP complex was isolated in pure form and characterized by chemical analysis. EXPERIMENTAL Reagents and Apparatus The radionuclide 60Zn of high specific activity was obtained in chloride form from the Institute »Boris Kidric«, Vinca, Yugoslavia. Inactive CuS04, Cu(NOah and ZnC12 solutions were standardized gravimetrically and by complexometric titrations. The synthesis of MOABP was descr.ibed earlier12 • Its solution in chloroform served as organic phase. All chemicals used were of analytical grade. The y-activity of the radioactive zinc was counted on a well-type y-scintillation counter with a NaI/Tl crystal. The absorbance measurements were made on a Beckman Spectrophotometer, Model DU-2, using a 1 cm quartz transmission cell. The IR spectra were recorded on a Perkin-Elmer IR Spectrophotometer, model 257. Isolation of Copper(II)-MOABP Complex The extractable complex of copper was prepared by shaking equal volumes of a 0.05 M solution of MOABP in chloroform and a 0.1 M solution of a copper (II) salt. The acidity of the aqueous phase was previously adjuste<;l. to pH = 5. The organic phase was separated and the chloroform evaporated in vacuo. The yellow-greenish complex was recrystallized from a chloroform-petroleum ether (1 : 1) mixture. Anal. C42HssN20GP2Cu (812.39) calc'd: C 62.09; H 7.20; N 3.45; P 7.62; Cu 7.820/o. found: C 62.28; H 7.28; N 3.49; P 7.50; Cu 7.450/o. Procedure for the Spectrophotometric Determination of Copper(II) An aqueous solution (8 ml), contaifting 0.05-0.5 mg of copper (II), ris adjusted to approximately 5 <pH< 6 a..."ld stabilized with an acetate buffer (2 ml), pH = 5.5. It is then extracted with 0.01 M solution of MOABP in chloroform (5 ml) for 2 min. The chloroform layer is transferred into a 10 ml volumetric flack. To extract the remaining traces of copper, the aqueous phase is extracted with chloroform (3 ml) , the chloroform extracts are combined. diluted to volume with chloroform, and the absorbance of the complex is measured at 371 nm. Procedure for the Separation of Zinc from Copper Irradiated metalic copper, used as a target for 65Zn, is disolved in 2 M HN03. The excess of the acid is neutralized, and a solution of potassium cyanide is added. To prevent the extraction. of copper, the molar ratio of copper to cyanide has to be at least 1 : 50. The solution is adjusted to pH = 5.5, and is then extracted with an equal volume .of 0.05 M solution of MOABP in chloroform for 2 min. Under these circumstances, zinc is quantitatively extracted into the organic phase, while copper remains in the aqueous phase. Reextraction of zinc can be carried out with 1 M hydrochloric or any other mineral acid. RESULTS AND DISCUSSION Extraction and Spectrophotometric Determination of Copper Extraction of copper(II) as a function of hydrochloric acid concentration, with MOABP dissolved in chloroform, is shown in Fig. 1. Copper is quanti-tatively extracted only from a weakly acidic solution having a pH in the range 4.5 ~ pH ~ 6.2. The same results were obtained with sulfuric and nitric acid and are therefore not presented. The reextraction of copper can be carried out with a 1 M mineral acid. The absorbance of the copper(II)-MOABP complex is also dependent on the acidity of the aqueous solution from which copper is being extracted, and DETERMINATION OF COPPER (II) 595 is the highest in the range 4.5 ~ pH ~ 6.2, as is shown in F1g. 2. In the expe-riments this pH was maintained with acetate buffer because -it has been found that these anions do not interfere with the extractiion of copper. The solution 100 80 60 -,, %E '0 02 A 20 0.1 -6 -1. -2 log [HCI] pH Fig. 1. Extraction of Cu(II) (2 ·10-• M) from hydrochloric acid solution with MOABP (5 ·10-2 M) dissolved in chlQroform. Fig, 2. Effect of pH in the aqueous phase on the absorbance of Cu(II) -MOABP complex i n chlo-roform. Concn. of Cu(II) 2 ·10-• M; MOABP 5·10-2 M . of the complex in chloroform is yellow colored with the maximum absorbance at 371 nm (Fig. 3.), and the molar absorptivity 1400. It follows the Lambed--Beer's law in the whole range of concentrations studied. The complex is stable in solution and the absorbance did not change even after several days of standing. 0.6 A 0., 0.2 3' 0 360 380 l OO '10 1.1.0 '60 lBO 500 520 ;\/nm Fig. 3. Absorption spectrum of Cu(II)-MOABP complex in chloroform. 596 B . TAMHINA ET AL. Factors Influencing the Absorbance of Cu(II)-MOABP Complex In ·order to obtain the quantitative extraction of copper and the reprodu-cible aibsorbance readings, the concentration of MOABP must be at least 15 times higher than that of copper. A still larger excess of MOABP has no further influence on the absorbance values. The influence of various anions on the spectrophotometric determination of copper is shown in Table I. Chloride, su1phate, nitrate, bromide, perchlorate, acetate and tartrate do not interfere. Citrate, pho,Sphate and thiocyanate inter-fere only when they are present in a high concentration. Cyanide, oxalate, ethylenediaminetetraaceta te (EDT A) and diaminocyclohexanetetraacetate (DCTA) interfere strongly and they must be absent. TABLE I Influence of Anions on the Spectrophotometric Determination of Copper (II) . Concentration of Cu (II) 2 · 10-4 M; MOABP 5 · 10-2 M. pH of the Aqueous Phase 5.5. Anion chloride sulphate nitrate bromide perchlorate acetate tartrate citrate phosphate thiocyanate oxalate EDTA DCTA cyanide Copper : anion molar ratio 1 : 1000 1 : 1000 1 : 1000 1 : 1000 1 : 1000 1· : 1000 1: 1000 1: 1000 1: 500 1 : 100 1: 50 1: 10 1 : 1000 1: 500 1 : 200 1: 100 1 : 10 1 : 1000 1 : 100 1: 50 1 : 10 1 : 1000 1 : 100 1 : 10 1 : 1 1: 100 1: 10 1 : 1 1: 100 1 : 10 1 : 1 1: 100 1: 80 1: 50 1: 5 1 : 1 Absorbance at 371 nm 0.270 0.269 0.270 0.270 0.269 0.268 0.270 0.270 0.050 0.125 0.260 0.265 0.269 0.140 0.180 0.195 0.265 0.269 0.094 0.255 0.260 0.262 0.030 0.023 0.030 0.030 0.006 0.004 0.010 0.005 0.014 0.017 0.000 0.000 0.010 0.210 0.269 DETERMINATION OF COPPER (II) 597 The influence of cations on the spectrophotometric determination of copper is presented in Table II. Most of the cations studied do not interfere even when they are present in a moderate excess with respect to copper. Aluminium(III), TABLE II Influence of Cations on the Spectrophotometric Determination of Copper (II). Concentration of Cu (II) 2 · 10·4 M; MOABP 5 · 10-2 M. pH of the Aqueous Phase 5.5. Cation -K (I) Na (I) NH4 (I) Mg (II) Ni (II) Ba (II) Al (III) Cr (III) Ca (II) Co (II) Mn(II) Bi (III) V(V) Ti (IV) Zr (IV) Fe (III) Ga (III) Nb (V)* U (VI) Zn (II) Copper : cation molar ratio -1 : 1000 1 : 1000 1 : 1000 1 : 1000 1 : 100 1 : 1000 1 : 100 1 : 1000 1 : 100 1 : 50 1 : 50 1 : 100 1: 1000 1 : 100 1 : 10 1 : 50 1 : 5(), 1 : 100 1 : 10 1 : 100 1 : 100 1 : 10 1 : 100 1 : 100 1 : 10 1 : 10 1 : 1 1 : 10 1 : 1 1 : 10 1 : 1 1 : 10 1 : 1 • Added as tartrate complex Absorbance at 371 nm 0.270 0.269 0.268 0.269 0.235 0.268 0.233 0.267 0.245 0.260 0.267 0.270 0.270 0.147 0.240 0.268 0.270 0.267 0.240 0.263 0.272 0.250 0.265 0.273 >2 1.800 0.200 0.269 0.225 0.268 0.225 0.265 0.098 · 0.267 chromium(III), cobalt(II) and manganese(II) do not exhibit any interference even if their concentration exceeds 50 times that of copper, providing there is an excess of MOABP to prevent the formation of insoluble complexes between metals and MOABP. Cations which are extracted very much under these conditions, like gallium(III), niobium(V), zinc(II) and uranium(VI), compete with the extraction of copper aind may therefore bring about a decrease of the absorbance values. This interference could easily be overcome by using a more concentrated MOABP solution. Among all cations investigated only 598 B. TAMHINA ET AL. iron(III) influences the determination of copper even if present in smaller quantities. Determination of Cu(II)-MOABP Ratio in the Extractable Complex The ratio of copper t,o MOABP in the extractable complex was determined by three spectrophotometric methods and by extraction dependence study. The ratio was determined by Job's method of continuous variations,13 by the molar ratio method,14 and by the slope ratio method.14 The results obtained are shown in Figs. 4, 5 and 6, respectively. Since MOABP is practically insoluble in water, for all these experiments the appropriate solutions of MOABP in chloroform were shaken with aqueous solution of copper. Then the organic layer was separated and its absorbance measured spectrophoto-1.2 •• --~,c---~,~, -~OL6-~0~8 -~LO·----~-(Cuj [Cu].(MOABP] O.l __!.._.__l__ _ _J -- = _J_j_J _ __l _ _ 2 4 6 I> 10 !1 20 30 'O SO [MOABP] ~Fig. 4. Determination of composition of (Cu(II)-MOABP complex by Job's method. Concn. of (0) [CU]+ [MOABP] = 3 ·10•3 M ; (i'.',) [Cu] + [MOABPJ = 4·10-3 M; (0) [Cu] + [MOABP] = 6·10· :l :M; pH of aqueous solution 5.·5 (acetate buffer). Fig. 5. Determination of composition of Cu(II)-MOABP complex by molar ratio method. Concn. of Cu(II) constant 2-10-• M; concn. of MOABP varied. pH of the aqueous phase 5.5 (acetate buffer). 0.7 06 A OT , ].jY 02 0.1 ~~-~~-~-~~.L____l-~---Q2 ~ M M tO L2 U ~ cxlOo/M Fig. 6. Determination of composition of Cu(II)-MOABP complex by slope ratio method. (0) MOABP concn. 2-10-• M. Cu(Il) concn. varied, <•) MOABP cocn. varied, Cu(II) concn. 2·10-• M; (0) MOABP concn. 8·10-5 M, Cu(II) concn. varied; <•) MOABP concn. varied, Cu\II) concn. 8·10-5 M. metrically. The experimental results indicate a complex with 1 : 2 ratio of Cu(II) to MOABP, and formula Cu[C6H 5NHCH(CGH5)PO(OC8Hd0] 2 (marked DETERMINATION OF COPPER (II) 599 later as CuA2). This complex was also isolated from the organic phase as described in the Experimental Section. The broad shallow absorption of the OH vibration in the 2500-2700 cm-1 range characteristic for the ligand mole-cule is not evident in the IR spectrum of the complex. The P-+0 frequency shift of 35 cm-1 provides support that this group is involved in the complex formation. The dependence of the distribution ratio, D, for copper on the MOABP concentration in the organic phase is shown in F ig. 7. A curve with a slope ,of 0 en -" -1 -I - _ _!__ - _ _J_ - - · -----1._____ - --- - . · 3 -2 -I log (MOABP] Fig . 7. Dependence of d istribu tion r a t io, D , of Cu(II) (2·10-• M) on the MOABP concn. in the organic pha se. Initial acidity of the a queous phase (0) pH = 2.5; (6 ) pH = 2.0. 2 was obtained, indicating that D is proportional to the second power of the extractant concentration. Taking into account that MOABP is actually dimer-ized in chloroform 11 , the stoichiometry of the copper extraction can be repre-sented as: Cu~:q> + (HAL cu> ~ CuA2 <ol + 2H~qJ where (HA) 2 denotes dimeric form of MOABP. Separation of Zinc from Copper As shown in Fig. 1, copper is quantitatively extracted from very diluted mineral acids. Zinc is also extracted from the solutions with pH higher than 3.7 Their separation is, nevertheless, feasible if copper ions are masked with cyanide. The copper cyanide complex is soluble only in water and insoluble in chloroform. To prevent the competition between MOABP and cyanide, the 600 B. TAMHINA ET AL. molar concentration of the latter must exceed that of copper at least 50 times (Table I). It is shown in Table III that the excess of cyanide does not interfere with the extraction of zinc. Using this procedure it is possible to extract zinc from the aqueous solutions containing a large amount of copper. TABLE III Extraction of Zinc (II) in the Presence of Different Amounts of Copper (II) and Cyanide Ions. Concentration of Zn (II) 1 · 10·0 M; MOABP 5 · 10·3 M. pH of the Aqueous Phase 5.5. Cu(N03h concn. in l KCN concn. in I aqueous phase/M aqueous phase/M 1 . 10-4 1 . 10·3 5 . 10·3 1 . 10·2 5 . 10·2 1 . 10-1 O.Ql 0.1 0.5 1.0 5.0 10.0 REFERENCES Zinc extracted O/o 99.9 99.9 99.9 99.9 99.9 99.9 l. V. Jago di c and D. Gr den i c, J . Inorg. Nucl. Chem. 26 (1964) 1103. 2. M. J. Her a k and V. J ago d i c, Croat. Chem. Acta 36 (1964) 51. 3. V. Jago di c, M. M. Her a k and M. J . Her a k, Radiochim. Acta 6 (1966) 64. 4. M. M. Her a k, V. J a g o d i c and M. J. Her a k, Croat Chem. Acta 39 (1967) 89. 5. V. Jago di c, M. J. Her a k and :r. Rados e vi c, J. Less-Common Metals, 15 (1968) 371. 6. M. J . Her a k, N. Vu j i c i c and V. Jago di c, Mikrochim. Acta ((1969) 16. 7. M. J . Her a k and V. Jago di c, Proc. Int. Solv. Extr. Conf., The Hague 1971, 656. 8. V. Jago di c and M. J. Her a k, J . Inorg. Nucl. Chem. 33 (1971) 2641. 9. V. Jago di c, M. J. Her a k, B. Sip a 1 o and J. Rados e vi c, J . Inorg. Nucl. Chem. 33 (1971) 2651. 10. V. J a god i c and M. J ., Her a k, J. Inorg. Nucl. Chem. 32 (1970) 1323. 11. M. J. Her a k and V. Jago di c, J. Inorg. Nucl. Chem. 35 (1973) 995. 12. V. Jago di c, Chem. Ber. 93 (1960) 2308. 13. P. J ob, Ann. Chim. (Paris) 9 (1928) 113. 14. A. E. Harvey, Jr. and D. L. Manning, J. Amer. Chem. Soc. 72 (1950) 4488. IZVOD Odjeljivanje cinka od bakra metodom ekstrakcije i spektrofotometrijsko odredivanje bakra (II) pomocu monooktil-a-anilinobenzilfosfonata B. Tamhina, M. J. Herak i V . Jagodic Proucavana je ekstrakcija bakra (II) iz razrijedenih otopina klorovodicne, du-s1cne i sumporne kiseline pomocu otopine monooktil-a-anilinobenzilfosfonata (MOABP) u kloroformu. Bakar se kvantitativno ekstrahira iz otopina s pH u rasponu 4.5 <pH < 6.2. Iako se cink takoder ekstrahira iz razrijedenih otopina mineralnih kiselina, odjeljivanje cinka od velikih koliCina bakra izvedivo je u prisutnosti cijanida. Bakar (II) i MOABP tvore stabilan foto obojeni kompleks cija otopina u kloro-formu slijedi Lambert-Beerov zakon. Razraden je postupak za spektrofotometrijsko odredivanje bakra i ispitan je utjecaj raznih kationa i aniona na apsorpciju kompleksa. DETERMINATION OF COPPER (II) 601 Omjer bakra i MOABP u kompleksu je utvrden spektrofotometrijski i iz odnosa distribucijskog omjera bakra prema koncentraciji MOABP u organskoj fazi. U cistom stanju izdvojen je kompleks s MOABP u kojemu su 2 molekule liganda vezane s ionom bakra. ZAVOD ZA ANALITICKU KEMIJU, PRIRODOSLOVNO· MATEMATICKI FAKULTET, ZAGREB i INSTITUT »RUDER BOSKOVIC«, 41000 ZAGREB Primljeno 8. listopada 1973. 

Solvent Extraction and Separation of Zinc from Copper and Direct Spectrophotometric Determination of Copper (II) by Monooctyl a -Anilinobenzylphosphonate

Solvent Extraction and Separation of Zinc from Copper and Direct Spectrophotometric Determination of Copper (II) by Monooctyl a -Anilinobenzylphosphonate

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