Extraction of lead picrate by 18-crown-6 ether into various diluents: Examples of sub-analysis of overall extraction equilibrium based on component equilibria
作者:Yoshihiro Kudo、Yuu Takahashi、Chiya Numako、Shoichi Katsuta
DOI:10.1016/j.molliq.2014.01.017
日期:2014.6
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.