Extraction of Lanthanoids with Bis(2-ethylhexyl) Hydrogenphosphate -Equilibria in the Region of High Loading-
1982 Volume 1982 Issue 4 Pages 627
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1982 Volume 1982 Issue 4 Pages 627
Extraction of lanthanoids (Ln) with bis (2-ethylhexyl) hydrogenphosphate (D2EHPA, (C8H17O)2POOH) has been investigated in the region of high metal loading. Extracted species are polymerized and form gelatinous materials at high metal loading (Rtr>0.15) as shown in Fig.1. Table 1 indicates that the composition of the polymerized species is LnX3 (X: (C8H17O)2POO). Fig.3-(a) indicates that the extractant dependence of the distribution ratio of a lanthanoid is 2.5 power in benzene, and therefore the extraction reaction is represented as Eq. (2) (Ln (a)8++ 5/2 (HX)2(o) ↔ LnX3⋅2 HX(o) + 3 H(a)+). Fig.4 (a) shows that the concentration of a lanthanoid in the organic phase is of first order in the D2EHPA concen tration in the presence of gelatinous materials when benzene is a diluent, and therefore the equilibrium between the organic phase and the gelatinous materials is represented as Eq. (3)(1/p (LnX3)p(g) + (HX)2(o) ↔ LnXLnX3⋅2 HX(o)), where p is the degree of polymerization. The dependence on D2EHPA concentration is lower in heptane than in benzene as shown in Fig.3-(b), 4-(b) and 5-(b). The difference can be explained by the fact that the association number of D2EHPA in heptane is more than 2.
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