1973 Volume 46 Issue 12 Pages 3772-3779
The solvent extraction of trace amounts of various metal ions with STTA (1,1,1-trifluoro-4-(2-thienyl)-4-mercapto-3-buten-2-one) in the presence or in the absence of TOPO (tri-n-octylphosphine oxide) has been investigated. The results are as follows: (a) The apparent extraction constant of each metal–STTA chelate in cyclohexane, logK, increases, and their pH 1⁄2 values decrease, in the order of: Cd(II)-In(III)-Zn(II)-Fe(III)-Ni(II)-Ag(I)-Bi(III)-Co(II)-Pb(II)-Cu(II)-Hg(II). This order was found to hold also in the back-extraction, except for cobalt, which was not back-extracted even with 1–12 M HCl. The other metals, Au(III), and Pd(II), could also be extracted as their STTA chelates. (b) The kind of the solvent has an effect to the lowest pH value where the metal STTA chelates begin to be extracted; the lowest pH is shifted to a higher value in the order of: C6H12, CCl4, MIBK, C6H6 and CHCl3. (c) The distribution coefficient, Pr, and the enol dissociation constant, Ka, of STTA were logPr=2.99 (10−3 M STTA in cyclohexane-0.1 M NaClO4-pH 1.0) and logKa=−4.38 (10−4 M STTA in 0.12 M HCl, 0.1 M CH3COOH (pH 4.5) and 0.1 M NaOH-C2H5OH (1/5, v/v) solution) at 20 °C. (d) The extraction equilibrium of Zn seemed to be rapid, that of Ni showed its rate-determining step to be the formation of Ni(STTA)+, and that of Co seemed to be accompanied by a transformation of Co(STTA)2 to Co(STTA)3. (e) In the metal–STTA(0.001 M)-TOPO(0.01 M)–cyclohexane system, the |ΔpH1⁄2| was found to be 0.45 for Ni, 1.95 for Zn, and 0.25 for Co. The Co–STTA–TOPO chelate could be back-extracted to some degree with 1 M HCl. The extracted species were ascertained to be Zn(STTA)2, Zn(STTA)2TOPO, Ni(STTA)2, Co(STTA)2, Co(STTA)3, and Co(STTA)2TOPO. The stability constant of Zn(STTA)2 TOPO was found to be 6.05.
This article cannot obtain the latest cited-by information.