勝田 正一

The extraction of gold(III) from 0.10 mol dm(-3) hydrochloric acid into various aprotic ionic liquids (ILs) was investigated at 25 degrees C. Eleven kinds of ILs were examined as the extraction solvents; the cations were 1-butyl-3-methylimidazolium ([BMIm](+)), 1-hexyl-3-methylimidazolium, 1-methyl-3-octylimidazolium, 1-butyl-2,3-dimethylimidazolium, 1-butyl-1-methylpyrrolidinium, and methyltrioctylammonium; the anions were tetrafluoroborate, hexafluorophosphate, bis(trifluoromethanesulfonyl)amide ([NTf2](-)), and bis(pentafluoroethanesulfonyl)amide. The metal was extracted as anionic tetrachloroaurate ([AuCl4](-)) into all the nonprotic ILs with high distribution ratios (>100). The distribution ratio of gold(III) differs largely (480-fold at most) depending on the IL species and also depends on the amount of extracted gold(III). These dependences of the distribution ratio were quantitatively explained as functions of the solubility product of the IL used, where we considered the equilibrium model comprising the ion pair extraction of [AuCl4](-) with the IL cation in the aqueous phase and the ion exchange of [AuCl4](-) with the IL anion in the IL phase. From a practical purpose, the back extraction of gold(III) from an IL ([BMIm][NTf2]) phase was also examined; nearly quantitative stripping was possible using acidic thiourea solutions.

The adsorption behavior of Be(II) on CuO nanoparticles dispersed in water was studied as a model for colloid formation of radioactive Be-7 nuclides in the cooling water used for electromagnets at high-energy proton accelerator facilities. An aqueous Be(II) solution and commercially available CuO nanoparticles were mixed, and the adsorption of Be(II) on CuO was quantitatively examined. From a detailed analysis of the adsorption data measured as a function of the pH, it was confirmed that Be(II) is adsorbed on the CuO nanoparticles by complex formation with the hydroxyl groups on the CuO surface (>S-OH) according to the following equation: n > S-OH + Be2+ (sic) (> S-O)(n) Be(2-n)+ + nH(+) (n = 2,3) S : solid surface. The surface-complexation constants corresponding to the above equilibrium, beta((s,2)) and beta((s,3)), were determined for four types of CuO nanoparticles. The beta((s,2)) value was almost independent of the type of nanoparticle, whereas the beta((s,3)) values varied with the particle size. These complexation constants successfully explain Be-7 colloid formation in the cooling water used for electromagnets at the 12-GeV proton accelerator facility.

Extraction constants for lead picrate, PbPic(2), with 18-crown-6 ether (L) from aqueous solutions at a narrow range of ionic strength (I) into eleven diluents were determined at 298 K by AAS measurements. These constants were defined as K-ex=[PbLPic(2)](0)/([Pb2+][L](0)[Pic(-)](2)) and K-ex +/-=[PbLPic(+)](0)[Pic(-)](0)/([Pb2+][L](0)[Pic(-)](2)), where the subscript "o" denotes the organic phase (or diluent). The ratio, K-ex/K-ex +/-, gave an ion-pair formation constant for PbLPic(o)(+) + Pic(o)(-)=PbLPic(2,o) at the averaged value of ionic strength (I-o) of the organic phase. A plot of log K-ex +/- versus log k(D.pc) yielded a straight line with the slope of 2.1 in a series of the diluents employed; K-D,K-Pic refers to an apparent distribution constant of Pic- between the aqueous and organic phases and its values were experimentally determined. The slope indicated that K-ex +/- is mainly controlled by the square of K-D,K-PIc when a thermodynamic cycle is assumed. The extraction constant based on the cycle was expressed as K-ex +/-=(K-D,K-Pic)(KD,MKML,orgK1,org)-K-2, where KD,MKM,L,orgK1,org denotes the product of other component equilibrium-constants. Moreover, the relation of log K-D.Pic=alog (I-o/I) + b was experimentally found at a approximate to 1 and then an example of b was expressed theoretically. It was shown that Pb(II) can be separated from mixtures with Cd(II) in unit operation. (C) 2014 Elsevier B.V. All rights reserved.

Extraction constants (K-ex and K-ex +/-) of CdBr2 into eleven diluents and Cd (Pic)(2) into eight diluents by 18-crown-6 ether (18C6) and apparent distribution constants (K-D,K-A) of pairing anions (A(-)) were determined at 25 degrees C. Here, K-ex, K-ex +/-, and K-D,K-A were defined as [CdLA(2)](o)/[Cd2+][L](o)[A(-)](2), [CdLA(+)](o)[A(-)](o)/[Cd2+][L](o)[A(-)](2), and [A(-)](o)/[A(-)], respectively: L=18C6, A(-)=Br- and picrate ion (Pic(-)), and the subscript "o" denotes the diluent phase. Also, K-2(org) was estimated from the ratio K-ex/K-ex +/-. Using the two extraction constants and their component equilibrium ones, extraction-abilities and -selectivities of the diluents for the above extraction systems were discussed. From the K-D,K-A values, the distribution constants of cationic ion-pairs CdLA(+) into 1,2-dichloroethane (DCE) and dichloromethane (DCM) were also standardized and thereby ion-transfer potentials of CdLA(+) at water (w)/DCE and w/DCM interfaces were estimated. Further, interactions of neutral ion-pairs CdLA(2) with w molecules were examined with cohesive energy densities obtained from the plots of log K-ex,K-ip versus log K-D,K-L, where K-ex,K-ip and K-D,K-L denote an ion-pair extraction constant of CdLA(2) into the diluents and the distribution one of 18C6, respectively. (C) 2012 Elsevier B.V. All rights reserved.

Extraction constants, defined as K-ex = [HPic](o)/[H+][Pic(-)], for picric acid (HPic) into ten diluents were spectrophotometrically determined at 298K, where the subscript "o" refers to an organic (o) phase which is composed of the diluent. Their values for the HPic extraction into benzene and chloroform were fairly consistent with those reported before. From the K-ex values, distribution constants (K-D,K-HPic) of HPic into the o phases were estimated using the thermodynamic relation K-ex = K-D,K-HPic,K-HPic, where K-HPic corresponds to a protonation constant of Pic(-) in water. Thereby, contributions of functional groups, such as -Cl and -CH3, involved in the diluents molecules to K-D,K-HPic were discussed. The same discussion was also applied for the distribution of the ion pair, composed of CdPic(2) and 18-crown-6 ether, into the diluents.

The extractabilities of aluminium(III), gallium(III), and indium(III) from hydrochloric acid solutions were investigated using a mixture of two protic ionic liquids, trioctylammonium bis(trifluoromethanesulfonyl)amide ([TOAHI][NTf2]) and trioctylammonium nitrate ([TOAH][NO3]). At a HCl concentration of 4 mol L-1 or more, gallium(III) was nearly quantitatively extracted and the extractability order was Ga > Al >> In. The extractability of gallium(III) increased with increasing [TOAH][NO3] content in the mixed ionic liquid. The extracted gallium(III) was quantitatively stripped with aqueous nitric acid solutions. The separation and recovery of gallium(III) from hydrochloric acid solutions containing excess indium(III) was demonstrated using the mixed ionic liquid.

Extraction constants (K,) for complex ions (MLz+) of L = 15-crown-5 ether (15C5), benzo-15C5, 18-crown-6 ether (18C6), benzo-18C6, dibenzo-18C6, or dibenzo-24-crown-8 ether (DB24C8) with A(-) = picrate ion (Pic(-)) into nitrobenzene (NB) were evaluated at z = 1 and 2. Here, the following thermodynamic relation was used for their evaluation: K-ex +/- = [MLz+]NB)(z)/([Mz+][L](NB)[A(-)](z))=K-D,K-M(K-D,K-A)(z)beta(NB)(1); K-D,K-j and beta(NB)(1) denote an individual distribution constant of species j (=Mz+, A(-)) into the NB phases and a stability constant for MLz+ in the phases. Using these results and the number of water (w) molecules co-extracted with M+, L, and ML+ into the NB phases, an effect of the w molecules released with the ML+ formation in the NB phases on K-ex +/- was discussed. The above results were also applied for the prediction of an actual separation of Ba2+ from Sr2+ or Ca2+, using DB24C8 or 18C6 as L, Pic- as A-, and NB as diluent. Then, it was predicted that DB24C8 is more effective as L for the separation of Ba2+ from Ca2+ than 18C6. No effective L for the separation of Cs+ from Na+ was found out, using A(-) = I- and NB as the diluent. (C) 2012 Elsevier B.V. All rights reserved.

The ion-pair formation constants (K(MLX)(0)/mol(-1) dm(3)) of CdL(2+) with Br(-) or NaL(+) with N,N-diethyldithiocarbamate ion (DDTC(-)) in water were determined potentiometrically at 25 degrees C; ionic strength (I)-> 0: L denotes 18-crown-6 ether (18C6) and its mono-benzo derivative for the CdBr(2)-L system and 15-crown-5 ether and 18C6 for the NaDDTC-L one. The formation constant corresponding to the simple salt, NaDDTC, in water was also determined at I -> 0 Using the log K(CdLX)(0) values of CdLCl(+), CdLBr(+), CdLPic(+), and CdLSO(4), then CdL(2+) and picrate ion (Pic(-)) in water have been classified with the hard and soft acids and bases principle, where the values were available in the literature, except for CdLBr(+). The same classification was examined in NaX-L systems with X(-) = DDTC(-), trifluoroacetate ion, MnO(4)(-), ReO(4)(-), Pic(-), and BPh(4)(-) and the AgPic-L one. Consequently, CdL(2+), NaL(+), and AgL(+) were classified as the hard acids, while Pic(-) and BPh(4)(-) as the hard bases. These results reflected the reactivities of the complex ions in ion-pair formation with X(-) and SO(4)(2-) in water.

Sodium permanganate, sodium picrate (NaPic), Bu(4)NPic, Me(4)NPic, and Et(4)NPic were extracted at an ionic strength of 2 x 10(-5) to 0.08 mol dm(-3) and 25 degrees C from water (w)-phases into the organic (o)-ones, 1,2-dichloroethane (DCE) and nitrobenzene (NB). Thereby, apparent distribution constants (K(D,+/-)) of the anions (A(-)) or the cations (M(+)) and ion-pair formation ones (K(MA)(org)) of the univalent salts (MA) in the o-phases were determined at 25 degrees C, where K(D,+/-) = ([A(-)](o)[M(+)](o)/[A(-)][M(+)])(1/2) = (K(D,A)K(D,M))(1/2) and K(MA)(org) = [MA](o)/[M(+)](o)[A(-)](o). Also, the K(ex) and K(D,MA) values with A(-) = Pic(-), MnO(4)(-) were estimated from the relations K(ex) (= [MA](o)/[M(+)][A(-)]) = K(MA)(org)(K(D,,+/-))(2) and = K(MA)K(D,MA), respectively. Standard potentials (Delta phi(0)(u)) for ion transfers at the w/DCE and w/NB interfaces were evaluated from the log K(D,A) or log K(D,M) values by assuming the relations K(D,Pic) = K(D,E14N) and = K(D,Me4N), respectively. The thus-obtained Delta phi(0)(u) values, especially for the w/DCE system, were in good agreement with the values based on the extra-thermodynamic assumption for Ph(4)As(+) and BPh(4)(-) transfers at the interfaces. In the present extraction systems, the ion-pair formation of MA in the w- and o-phases was less effective in the determination of their distribution constants into the two o-phases.

Ion-pair formation constants (K(n)(0), n = 1, 2) of Na(2)SO(4), Na(2)S(2)O(3), Na(2)CrO(4), CaCl(2), CdCl(2), CdBr(2), and Cdl(2) in water were determined at 298 K and an ionic strength of 0 mol.dm(-3) by potentiometry with Na(+)-, Cl(-)-, Br(-)-, and I(-)-selective electrodes. Simultaneously, equations for the K(n)(0) determination based on the DeFord-Hume method were derived. The thus-obtained K1 values for Na2SO4, Na2S203, CdCl(2),, and CaCl(2), were compared with those reported before, and the validity of their values was confirmed. interactions of Na(+) with oxo anions (X(2-)) and Cd(2+) with the halide ions in water were characterized by considering hydration to and Coulombic forces acting between these ions. Then, a difference in K(1)(0) between CdI(+) and NaSO(4)(-) was interpreted as that in the Coulombic force between the pairing ions. Also, the K(1)(0) difference between Na(+)BPh(4)(-) and Ph(4)As(+)Cl(-) or CaCl(+) and NaSO(4)(-) was examined by using a thermodynamic cycle of these salts in a water/nitrobenzene (NB) distribution system. Furthermore, the distribution constants in the NB phases were evaluated.

overall ion-pair formation constants (beta/mol(-2) dm(6)) of CdL(2+) with picrate ion (Pic(-)) and Cl(-) in water (w) were determined at 298 K potentiometrically, where L denotes 18-crown-6 ether (18C6) or benzo-18C6 (B18C6). These values at ionic strength (l) -> zero were 1.8 x 10(7) for Cd(18C6)(Pic)(2); 2.3 x 10(7) for Cd(B18C6)(Pic)(2); 1.4 x 10(6) for Cd(18C6)Cl(2); 2.7 x 10(6) for Cd(B18C6)Cl(2). Using the beta(2) value for CdL(Pic)(2) at L = B18C6 and other equilibrium constants. extraction constants {Kex(k), k (stoichiometric number of L) = 1, 2} and an association one (K(ML2A2)) of CdL(Pic)(2) with L in benzene were re-calculated from the extraction data reported before: Kex(1) = [CdL (Pic)(2)]o/[Cd(2+)][L]o[Pic(-)](2) = 10(2.37), Kex(2)=[CdL(2)(Pic)(2)]o/[Cd(2+)][L]o(2)[Pic(-)](2)=10(4.21), and K(ML2A2)=[CdL(2) (Pic)(2)]o/[CdL(Pic)(2)]o[L]o = 70 at the acidic w-phase of l = 0.095 mol dm(-3) (HNO(3)). Here, the subscript "o" denotes the benzene phase. These values were somewhat larger than those reported previously. From a thermodynamic cycle of an extraction model proposed here, the distribution constant of Cd(B18C6)(Pic)(2) into benzene was calculated to be 10(-3.56). A difference (4.50) in logarithmic distribution constant between Cd(B18C6)(Pic)(2) and B18C6 suggested the stronger hydration of the former than the latter in the w-phase. (C) 2009 Elsevier B.V. All rights reserved.

Cohesive energy densities (C(w,MLA)/J cm(-3)) for ion-pair complexes (MLA: M(+) = Li(+) to Cs(+); w: water) with six crown ethers (L), such as 18-crown-6 ether (18C6), benzo-18C6, and dibenzo-24-crown-8 one, and A(-) = picrate were calculated at 298 K by a procedure that uses either (i) an equation rearranged from that underlying log K(D,MLA)-vs.-log K(D,L) Plots or (ii) intercepts of their plots and from both procedures. Here, K(D,MLA) and K(D,L) denote the distribution constants of MLA and L from w into a diluent, respectively. As additional MLA, Na(18C6)(2,4-dinitrophenolate) and Na(18C6)(2,6-dinitrophenolate) were employed for the present C(w,MLA) calculation. The C(w,MLA) values calculated from the two procedures agreed well, and they were proportional to the log(K(D,MLA))(-1) values. From the log K(D,MLA) values for dinitrophenolates and previously-reported values for Na(18C6)A, the hydrophobic property of some pairing anions, A(-), was ordered as F(3)CCO(2)(-) < ReO(4)(-) < MnO(4)(-) < 2,4-dinitrophenolate < 2,6-dinitrophenolate < picrate, and then discussed based on a relation with the log K(ex) values, where K(ex) shows the extraction constant (mol(-2) dm(6) unit) for Na(18C6)A into 1,2-dichloroethane.

The ion-pair formation constants {K-j(0): j = MA (metal salt), MLA} of NaO2CCF3 (Na(+)tfa(-)) and its ion-pair complexes (MLA) in water (w) were determined potentiometrically at 25 degrees C and an ionic strength (I) of zero. 15-Crown-5 (15C5), 18-crown-6 ethers (18C6), and their mono-benzo derivatives were used as crown ethers (L). The extraction of Natfa by these four L from w into 1,2-dichloroethane was done at 25 degrees C, and then the extraction constants (K-ex) for NaLtfa were calculated by using the K-j values, which were estimated from the corresponding K-j(0) ones at I of the w-phases, and other equilibrium constants. Also, the distribution constants (K-D,K-MLA) of NaLtfa between the two phases were obtained from a thermodynamic cycle expressing K-ex. An interaction of w-molecules with NaLA was considered using a relation of log K-D,K-MLA with log K-D,K-L, derived from the Scatchard-Hildebrand equation, where K-D,K-L denotes the distribution constant of L between the two phases. The interaction increased in the order of NaL (picrate) < free L <= NaLMO4 (M = Mn, Re) < NaLtfa for L = 15C5 and 18C6.

Theoretical equations were derived for the determination of ion-pair formation constants (K-0 in mol(-1).dm(3)) for 2:2 (M2+X2-) and 2:1 electrolytes and NIX with crown ethers (L) in water at an ionic strength of zero. The K-0 values were determined potentiometrically at 25 degrees C; CdSO4, CdCl2, Cd(picrate)(2), CaCl2, and Ca(picrate)(2) were used as the electrolytes, and CdL2+SO42- with L = 18-crown-6 ether (18C6) and benzo-18C6 were used as the ion-pair complexes. By examining the validity of the equations directly or indirectly, the K-0 values for CdSO4 and CdCl2 were compared with the corresponding literature. Consequently, it was evident that the derived equations are useful for the determination of K-0.

The ion-pair formation constant (K-MLA(0) in mol(-1) dm(3)) for Li(B15C5)(+) with a picrate ion (Pic(-)) in water was determined by potentiometry with a K+-selective electrode at 25 degrees C and an ionic strength of 0, where B15C5 denotes benzo-15-crown-5 ether. Using the concentration equilibrium constants, K-MLA, estimated from this value, the extraction constants (mol(-2) dm(6) unit) of about ten diluents were re-calculated from previously reported extraction data. Also, the distribution constants of an ion-pair complex, Li(B15C5)Pic, between water and the diluents were re-estimated. A disagreement in the determined KMLA value between a solvent-extraction method and potentiometry was explained in terms of the Scatchard-Hildebrand equation; it came from the fact that the hydration of Li(I) in Li(B15C5)Pic was larger than that of free B15C5 in water. Then, the previously determined value by the former method was re-estimated using the potentiometric KMLA value.