Abstract
Extraction of Pb(II) with picrate ion [Pic−] and 0, 0.58, 15, 48, or 97 mmol·dm−3 Cd(NO3)2 by benzo-18-crown-6 ether (B18C6; L as its symbol) into benzene (Bz) was studied. Three kinds of extraction constants, Kex, Kex±, and KPb/PbL (or Kex2±), were determined at 298 K: these constants were defined as [PbLPic2]Bz/P, [PbLPic+]Bz[Pic−]Bz/P, and [PbL2+]Bz/[Pb2+][L]Bz (or [PbL2+]Bz([Pic−]Bz)2/P), respectively. The symbol P shows [Pb2+][L]Bz[Pic−]2 and the subscript “Bz” denotes the Bz phase, Bz saturated with water. Simultaneously, conditional distribution constants, KD,Pic (=[Pic−]Bz/[Pic−]), of Pic− with distribution equilibrium-potential differences (dep) were determined. Then, based on the above four constants and others, the component equilibrium constants of K1,Bz (=[PbLPic+]Bz/[PbL2+]Bz[Pic−]Bz), K2,Bz (=[PbLPic2]Bz/[PbLPic+]Bz[Pic−]Bz), and KD,PbL (=[PbL2+]Bz/[PbL2+]) were obtained. Using these constants, the Pb(II) extraction with B18C6 under the co-presence of Cd(II) in the water phase was characterized. In such a characterization, I and IBz dependences on the constants were mainly discussed, where their symbols denote the ionic strength of the water phase and that of the Bz one, respectively.
Highlights
In extraction systems with crown compounds (L), some extraction constants, such as Kex and Kex±, have been employed for evaluating their extraction-abilities and -selectivities [1,2,3,4,5,6]
One of the authors reported the I and IDCE dependences of the Kex and Kex± values in the silver picrate (AgPic) extraction with benzo-18-crown-6 ether (B18C6) into 1,2-dichloroethane (DCE), where IDCE refers to the I value for the DCE phase [12]
= KPb/PbL 0 (KD,Pic 0 )2, Kex2± 0 = Kex± 0 /K1,Bz 0, and Kex± 0 = KPb/PbL 0 K1,Bz 0 (KD,Pic 0 )2, hold in the system. It seems that the linear equation is superior to the polynomial-type one for the IBz dependences of the above equilibrium constants, the R values with the former were less than those with the latter
Summary
In extraction systems with crown compounds (L), some extraction constants, such as Kex and Kex± , have been employed for evaluating their extraction-abilities and -selectivities [1,2,3,4,5,6]. For evaluating the ability and selectivity of L for its extraction, many studies have been present [1,2,3,4,5,6,7,8,9], but those for clarifying ionic strength (I) dependences of the equilibrium constants seemed to be few [10,11]. One of the authors reported the I and IDCE (with HNO3 as an I conditioner) dependences of the Kex and Kex± values in the silver picrate (AgPic) extraction with benzo-18-crown-6 ether (B18C6) into 1,2-dichloroethane (DCE), where IDCE refers to the I value for the DCE phase [12].
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