ANALYST, NOVEMBER 1986, VOL. 111 1261 Extraction of Iron( Ill), Gold( Ill), Gallium( Ill), Thallium( Ill), Antimony(V) and Antimony(ll1) from Hydrochloric Acid Solution with Crown Ethers* Hideko Koshima and Hiroshi Onishit University o f Tsu ku ba, Sa ku ra -m ura, Iba ra ki- ken 305, Japan C h I oroform solutions of d icyclo hexyl-I 8-crown-6 (DC 18C6), d i benzo- 18-crown-6 (DB 18C6) and 18-crown-6 (18C6) efficiently extracted iron(lll), gold(lll), gallium(lll), thallium(lll) and antimony(\/) from solution in hydrochloric acid. Extraction with 15-crown-5 (15C5) and 12-crown-4 (12C4) was poor. Antimony(l1l) in the presence of titanium(ll1) chloride was efficiently extracted only with DC18C6. When tervalent iron, gold, gallium and thallium were extracted from acidic lithium chloride solution, even 15C5 and 12C4 gave good extractabilities.The molar ratio of crown ether to the metal ions, except antimony(lll), in the extracted species is probably 1 : 1, and the metals are probably extracted as chloro complexes, e.g., HFeC14 and LiFeCI4. Iron and gallium in aluminium-base alloys were determined after their separation by DC18C6 extraction. Keywords: Crown ethers; extraction; chloro complexes; hydrochloric acid solution; acidic lithium chloride solution Crown ethers have been used extensively for the extraction of alkali and alkaline earth metals.l>2 In a previous paper,3 the extraction of iron(II1) from hydrochloric acid and acidic lithium chloride solutions with crown ethers was briefly described. Iron(II1) was thought to be extracted as chloro complex(es) , This assumption suggested the possibility of extracting other metals that form chloro complexes, e.g., gallium(II1) and thallium(II1). Extraction of gold(II1) with dibenzo-18-crown-6 (DB 18C6) from potassium chloride and lithium chloride solutions was reported by Gloe et ~ 1 .~ Vasilikiotis et aZ.5 have added crown ethers to isobutyl methyl ketone to improve the extraction of gold(II1) from hydro- chloric acid solution. More recently, Caletka et a1.6 have described the extraction of tantalum with dicyclohexyl-18- crown-6 (DC18C6) from fluoride solution. The purpose of this work was to demonstrate the validity of the above assumption. The nature of the extracted species was also investigated. Experimental Reagents and Apparatus Chloroform solutions of five crown ethers [DC18C6, DB18C6, 18-crown-6 (18C6), 15-crown-5 (15C5) and 12-crown-4 (12C4)] ,3 standard solutions of gold(1II) ,7 gallium(III), thallium(1,III) and antimony(II1) and 125Sb* were prepared as described previously. A standard iron(II1) solution for investi- gating the extracted species was prepared by dissolving FeC13.6H20 in water and standardising the solution iodime- trically.9 A standard lithium(1) solution was prepared by dissolving lithium choride in water.An NaI(T1) scintillation counter (well type), a flame atomic absorption (and emission) spectrometer (Nippon Jarrell-Ash, AA-782) and a spectro- photometer (Shimadzu UV-120-02, 1-cm cell) were used. Procedure Ten-millilitre aliquots (or 2-ml aliquots for gold and antimony) of 0.2 mM gold(III), 1 mM gallium(III), 0.1 mM thallium(II1, I) or 0.1 mM antimony(V, 111) containing an adequate activity of l25Sb in hydrochloric acid or 0.1 M hydrochloric acid - lithium chloride solution were shaken with an equal volume of 50 mM crown ether in chloroform for 5 min.* Presented at the 34th Annual Meeting of the Japan Society for Analytical Chemistry, Kobe, Japan, October 1985. t To whom correspondence should be addressed. Gold was determined by atomic absorption spectrometry (AAS) after diluting an aliquot of the organic phase with methanol. Gallium was determined by AAS after shaking the organic phase with 10 ml of 0.1 M hydrochloric acid for 5 min (back-extraction). Thallium was determined by AAS after shaking the organic phase with 10 ml of 0.05 M sulphuric acid - 0.1 M sodium sulphite for 5 min.Antimony was determined by measuring the count rate of 125Sb after transferring a 1-ml portion of the organic phase into a polyethylene test-tube. In order to investigate the extracted species, hydrogen ion, lithium and iron concentrations were determined by sodium hydroxide titration using phenolphthalein as an indicator, by flame emission spectrometry and by AAS, respectively. Results and Discussion Extraction of Gold(II1) Graphs of the extraction of gold(II1) from solution in hydrochloric acid with five crown ethers are shown in Fig. 1. A 100% amount of the gold(II1) with 18C6 and 59% with 15C5 were extracted from a 6 M hydrochloric acid solution after shaking for 0.5-5 min. The effect of the gold(II1) concentration on the extraction with DC18C6 and 18C6 from a 6 M hydrochloric acid solution was investigated; 10&97% of gold(II1) was extracted with both DC18C6 and 18C6 from 0.2-25 mM gold(II1) solutions.1 0 2 4 6 8 1 0 1 2 Initial HCI concentrationiM Fig. 1. Extraction of gold(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: AuIII, 0.2 mM in 2 ml of HCI; crown ether, 50 mM, 2 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E , 12C41262 ANALYST, NOVEMBER 1986, VOL. 111 The extraction behaviour of gold(II1) from 0.1 M hydro- chloric acid - lithium chloride solutions with DC18C6, DB18C6 and 18C6 (Fig. 2) was similar to that from the hydrochloric acid solutions (Fig. 1). 15C5 and 12C4 gave good extractabilities from lithium chloride solutions.Extraction of Gallium(II1) Graphs of the extraction of gallium(II1) from solution in hydrochloric acid with five crown ethers are shown in Fig. 3. The gallium(II1) that had been extracted with 18C6 and 15C5 from an 8 M hydrochloric acid solution could be back-extracted with an equal volume of 0.1 M hydrochloric acid. The shaking time of 1-10 min for both extraction and back-extraction gave over-all recoveries of 100% with 18C6 and of 73% with 15C5. A 100% amount of the gallium(II1) was extracted with DC18C6, DB18C6 and 18C6 from 1-25 mM gallium(II1) solutions in 8 M hydrochloric acid. When 225 mM gallium(II1) was extracted with DB18C6, the extracted species deposited during the extraction also occurred in the extraction of iron.3 The deposit was soluble in acetone.From 0.1 M hydrochloric acid - lithium chloride solutions, gallium(II1) was efficiently extracted not only with DC18C6, DB18C6 and 18C6 but also with 15C5 and 12C4 (Fig. 4). Extraction of Thallium(II1) Graphs of the extraction of thallium(II1) from solution in hydrochloric acid with five crown ethers are shown in Fig. 5. The thallium(II1) that had been extracted with 18C6 and DB18C6 from a 6 M hydrochloric acid solution could be back-extracted with an equal volume of 0.05 M sulphuric acid - 0.1 M sodium sulphite. The shaking time of 1-10 min for both extraction and back-extraction gave over-all recoveries of 96% with 18C6 and of 51% with DB18C6. A 9%92% amount of thallium(II1) with DC18C6 and 96-95% with 18C6 were extracted from 0.1-20 mM thallium(II1) solutions in 6 M hydrochloric acid.Thallium(1) in the presence of titanium(II1) chloride as a reducing agent was poorly extracted with DC18C6, DB18C6 and 18C6 from hydrochloric acid solutions (Fig. 6). Thallium [initially thallium(I)] in the absence of titanium(II1) chloride, however, was extracted to some extent with DC18C6 and 18C6 from 28 M hydrochloric acid solutions (Fig. 6). Thallium(1) is probably oxidised by air to thallium(II1) in the presence of DC18C6 and 18C6 and then extracted, as in the examples of the adsorption on activated carbon,s Amberlite XAD resins and Chelex 100.7 The extraction behaviour of thallium(II1) from 0.1 M hydrochloric acid - lithium chloride solutions with DC18C6, DB18C6 and 18C6 (Fig. 7) was similar to that from hydro- chloric acid solutions (Fig.5). In contrast, 15C5 and 12C4 gave good extractabilities. Extraction of Antimony(V) and Antimony(II1) Graphs of the extraction of antimony(V) with five crown ethers from hydrochloric acid solutions containing ammonium cerium(1V) sulphate as an oxidising agent are shown in Fig. 8. A 100% amount of antimony(V) was extracted with DC18C6 from a 10 M hydrochloric acid - 2 mM cerium(1V) solution after shaking for 1-5 min. The effect of antimony(V) concentration on the extraction was investigated: DC18C6 extracted 100% of antimony(V) from 0.1-5 mM antimony(V) solutions that were 10 M in hydrochloric acid and 2-15 mM in cerium(1V). When antimony(V) was extracted with 18C6 from 20.1 mM antimony(V) solutions in 2 6 M hydrochloric acid - 2 mM cerium(IV), the extracted species deposited.The extraction of 21 mM antimony with DB18C6 from 2 6 M hydrochloric acid - 5 mM cerium(1V) also produced deposits. Graphs of the extraction of antimony(II1) in the presence of titanium(II1) chloride are shown in Fig. 9. A 9694% amount of antimony(II1) was extracted with DC18C6 from 0.1-25 mM antimony(II1) solutions in 7 M hydrochloric acid - 20 g 1-1 titanium(II1) chloride. Nature of the Extracted Species The stoicheiometry of the extracted species was investigated by the molar ratio method. Plots of the percentage extraction of gold(III), gallium(III), thallium(II1) and antimony(V) with 18C6 or DC18C6 from hydrochloric acid solutions against the 2olkz--J 0 2 4 6 8 1 0 1 2 Initial LiCl concentrationh Fig.2. Extraction of gold(II1) from acidic lithium chloride solution with a chloroform solution of crown ether. Conditions: AuIII, 0.2 mM in 2 ml of 0.1 M HCI - LiCI; crown ether, 50 mM, 2 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E , 12C4 l o o r 80 r 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 3. Extraction of gallium(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: GaIII, 1 mM in 10 ml of HCI; crown ether, 50 mM, 10 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E , 12C4 Initial LiCl concentrationh Fig. 4. Extraction of gallium(II1) from acidic lithium chloride solution with a chloroform solution of crown ether. Conditions: GaIlf, 1 mM in 10 ml of 0.1 M HCI - LiCI; crown ether, 50 mM, 10 ml. A , DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E, 12C4ANALYST, NOVEMBER 1986, VOL.111 1263 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 5. Extraction of thallium(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: T P , 0.1 mM in 10 ml of HCI; crown ether, 50 mM, 10 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E, 12C4 8 40 0 .- +- 2 20 u 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 6. Extraction of thallium(1) and thallium (initially I) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: TI, 0.1 mM, 10 ml; crown ether, 50 mM, 10 ml. A, DC18C6, TI' in HCI - 20 g 1-1 TiC1,; B, DB18C6, TI1 in HCl - 20 g 1-l TiCl,; C, 18C6, Tll in HCI - 20 g 1-l TiC1,; D, DC18C6, T1 !njtially I in HCI; E, DB18C6, T1 (initially I) in HC1; and F, 18C6, TI !initially I] in HCl loot-@-+ 0 2 4 6 8 1 0 1 2 Initial LiCl concentrationh Fig.7. Extraction of thallium(II1) from acidic lithium chloride solution with a chloroform solution of crown ether. Conditions: T P , 0.1 mM in 0.1 M HC1 - LiC1, 10 rnl; crown ether, 50 mM, 10 ml. A, DC18C6; B, DB18C6; C, 18C6; D, 15C5; and E, 12C4 100 - 80 - 8 $ 60 2 fi 40 - .- c - u 20 - 0 2 4 6 8 1 0 1 2 Initial HCI concentrationh Fig. 8. Extraction of antimony(V) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: SbV in HCl - 2 mM CeIV, 2 ml; crown ether, 50 mM, 2 ml. A, DC18C6,O.l mM Sbv; B, DB18C6, 0.1 mM Sbv; C, 18C6, 0.01 mM Sbv; D, 15C5,O.l mM Sbv; and E, 12C4, 0.1 mM SbV & 60 0 .- U 40 X w 20 0 2 4 6 8 1 0 Initial HCI concentrationh Fig.9. Extraction of antimony(II1) from hydrochloric acid solution with a chloroform solution of crown ether. Conditions: SbIII, 0.1 mM in HCI - 2 g 1-1 TiCl,, 2 ml; crown ether, 50 mM, 2 ml. A, DC18C6; B, DB18C6; C, 18C6; and D, 15C5 I R A I 100 $? 80 C 0 .- 60 h 4- 4 0 , 0 1 2 3 Molar ratio, [crown ether1 [metal] Fig. 10. Plots of percentage extraction of metals with crown ether from hydrochloric acid solution against molar ratio of crown ether to metal. A, 2 ml of 10 mM Au"' in 6 M HC1,2 ml of 2-25 mM 18C6; B, 10 ml of 10 mM Gal" in 8 M HCI, 10 ml of 2-30 mM 18C6; C, 10 ml of 10 mM T P in 6 M HCI, 10 ml of 2-25 mM 18C6; D, 2 ml of 5 mM SbVin 10 M HCI - 11 mM CeIV, 2 ml of 1-15 mM DC18C6; and E, 2 ml of 10 mM SbIrl in 7 M HCI - 20 g 1-1 TiCI3, 2 ml of 2-30 mM DC18C6 ratio [crown ether]/[metal] gave sudden breaks at ratios of 1.0-1.2 (Fig.10). These results indicate a molar ratio of 1 : 1 in the extracted species. The same result was obtained with ir0n(II1).~ Plots of percentage extraction of gold(III), gal- lium( 111) and thallium( 111) from acidic lithium chloride solutions with 18C6 (figures omitted) were similar to those from hydrochloric acid solutions, also indicating a molar ratio of 1 : 1. Gloe et aZ.4 have shown that the gold(II1) species extracted from potassium chloride solution with DB18C6 has a molar ratio of 1 : 1. The ratio of DC18C6 to antimony(III), however, could not be determined (Fig. 10). On the assumption that HFeC14 is extracted with crown ether from hydrochloric acid solution and that LiFeC14 is extracted from lithium chloride solution, the molar ratios of hydrogen ion to iron and of lithium to iron in the organic phases were determined as follows.A hydrochloric acid or lithium chloride (not acidified) solution of 0.1 M iron(II1) was shaken with an equal volume of 0.1 M DC18C6 in chloroform. An aliquot of the separated organic phase was shaken with water (back-extraction) and hydrogen, lithium and iron ions were determined in the aqueous phase. The hydrogen ion concentration was calculated by the procedure of Nachtrieb and Conway.1° As shown in Table 1, a molar ratio of 1 : 1 was obtained for both [H+]/[Fe] and [Li]/[Fe]; this indicates the validity of the above assumption. The results shown in Table 1 also indicate that hydrogen and lithium ions are extracted with DC18C6 from hydrochloric acid and lithium chloride solutions not containing iron(III), but presumably HFeC14 and LiFeC14 are extracted preferentially.1264 ANALYST, NOVEMBER 1986, VOL.111 Table 1. Molar ratios of hydrogen ion or lithium to iron in the organic phase after extraction with DC18C6 Organic phase after extraction Aqueous solution Solution of Ferrr/M ~ M H C I . . . . . . 0 0 0.1 ~ M H C I . . . . . . 0 0 0.1 6 ~ L i C 1 . . . . . . 0 0 0.1 8 ~ L i C l . . . . . . 0 0 0.1 CHCl, solution of DC 18C6/~ 0 0.1 0.1 0 0.1 0.1 0 0.1 0.1 0 0.1 0.1 H+ or Li/M <0.001 0.036 0.093 <0.001 0.114 0.099 0 0.006 0.087 0 0.031 0.098 Molar ratio Fe/M or [Li] : [Fe] 0 0.95 : 1.0 0 0.098 0 1.0: 1.0 0 0.099 0 0.98 : 1.0 0 0.089 0 0.99 : 1.0 0 0.099 [H+I Table 2.Determination of iron and gallium in NBS aluminium-base alloys Present method* Relative Element Certified standard Sample determined value, Yo Average, ‘/O deviation, % SRM85b . . . . . . Fe 0.24 0.231 2.6 SRM858 . . . . . . Fe 0.078 0.0780 3.6 SRM85b . . . . . . Ga 0.019 0.0197 2.2 * Six aliquots of the sample solution were taken for each separation and determination. When iron(II1) and gallium(II1) solutions in hydrochloric acid were extracted with DB18C6 in chloroform, the extracted species deposited. The deposits were filtered off using a suction pump and were dried in a silica gel desiccator. The elemental analyses of the deposits were C 42.38, H 4.83, Fe 9.47 and C1 24.11; and C 41.34, H 4.74, Ga 11.65 and C1 23.11%, respectively.On the basis of the contents of C, Fe (or Ga) and C1, a DB18C6: Fe (or Ga) : C1 ratio of 1 : 1 : 4 is obtained. The absorption spectra of iron(III), gold(II1) and thal- lium(II1) extracted from solution in hydrochloric acid with the crown ethers were similar to those of the chloro complexes of the metals in hydrochloric acid solutions. The absorbances of iron(II1) in the organic phase at about 250, 320 and 360 nm were much higher than those in hydrochloric acid solution. These results suggest that the metals are extracted as the chloro complexes. Determination of Iron and Gallium in Aluminium-base Alloys The extraction method was applied to the separation and determination of iron and gallium in National Bureau of Standards (NBS) aluminium-base alloys.A 0.5-g sample was dissolved in hydrochloric acid (1 + 1) by heating and the solution was diluted to 50 ml with hydrochloric acid (1 + 1). A 5-ml aliquot of this solution was transferred into a separating funnel and 5 ml of concentrated hydrochloric acid were added. The solution was shaken with 5 ml of 50 mM DCl8C6 in chloroform for 5 min. The separated organic phase was shaken with 10 ml of 0.1 M hydrochloric acid for 5 min and the aqueous phase (back-extract) was adjusted to 20 ml with 0.1 M hydrochloric acid. Iron and gallium were then determined by AAS and spectrophotometry with Rhodamine B ,I1 respec- tively. The calibration graphs were established without the extractive separation. The results are shown in Table 2. The authors thank the Radioisotope Centre of the University of Tsukuba for permitting the tracer work. The elemental analysis was carried out by the Chemical Analysis Centre of the University. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Kolthoff, I. M., Anal. Chem., 1979, 51, 1R. Cheng, K. L., Ueno, K., and Imamura, T., “CRC Handbook of Organic Analytical Reagents,” CRC Press, Boca Raton, FL, 1982, p. 127. Koshima, H., and Onishi, H., Anal. Sci., 1985, 1, 389. Gloe, K., Miihl, P., Kholkin, A. I., Meerbote, M., and Beger, J., Isotopenpraxis, 1982, 18: 170. Vasilikiotis, G. S . , Papadoyannis, I. N., and Kouimtzis, Th. A., Microchem. J., 1984, 29, 356. Caletka, R., Hausbeck, R., and Krivan, V., Fresenius 2. Anal. Chem., 1985, 320, 665. Koshima, H., Anal. Sci., 1986, 2, 255. Koshima, H., and Onishi, H., Anal. Sci., 1985, 1, 237. Japanese Industrial Standard, JIS K 8142, 1976. Nachtrieb, N. H., and Conway, J. G., J. Am. Chem. SOC., 1948,70, 3547. Hasegawa, Y., Inagake, T., Karasawa, Y., and Fujita, A., Talanta, 1983, 30, 721. Paper A41147 Received May 27th, 1986 Accepted June 16th, I984