Extraction of metal cations

The results of the extraction of metal cations are summarized in Table 3. The 4b showed the selectivity toward Fe " cation and cannot act as an extractant for Fe " at pH 2.2. The extraction of Fe cation with 4b was increased with increasing pH, but the Fe cation ratios at all pH decrease than that of 2b and 3b. The results suggested that the conformation of 4b and the C=0 groups in the polymer affected the extraction of Fe in this process. 

Table 3 Extraction of Metal Cations with Ligands ...

Martinet, L., Berthon, L., Peineau, N., Madic, C., Zemb, T. 2002. Aggregation of the solvates formed in liquid-liquid extraction of metallic cations by malonamides Study of the Nd(N03)3/H20/LiN03/DMDBTDMA/dodecane system. In Proc ISEC 02. Sole,... 

Figure 6. The dimers formed by phosphorus(V) acids in non-polar solvents, (A) and the structurally related pseudo-chelates (B) formed on extraction of metal cations.

Extraction of metal cations Me from the sofid can also lead to creation of surface hydroxyls, with n OH groups created per Me species removed, in agreement with the rule of charge preservation. Typically, this chemistry can be formulated as an exchange reaction. However, more comphcated situations are also encoimtered. For example, extraction of framework Al ions from zeolites leads to the formation of so-called silanol nests (Figure 2.2). A perfect nest should consist of four Si—OH groups (26). 

An example of nonideal oiganic-iihase behavior arises with di-2-ethylhexyl phosphoric acid (DEHPA) in the extraction of metal cations. E ilibrium data of Troyer for extraction of copper in die presence of nickel from sulfote solution into xylene solutions of DEHFA are shown in Fig. 8.3-10. Although the organic-phase copper concentration would be expected to rise in proportion to that in the aqueous phase. 

It should be realized that the field of liquid-liquid extraction of metallic cations, basic and applied, is a very large one—even if the systems are restricted to those employing an acidic phosphorus-based extractant and the rare earths are the only metals considered. So the picture of the field presented here should not, in any sense, be considered representative. It is, rather, a reflection of our particular interests, directed by our dual love of coordination chemistry and of the rare earths. 

Figure 5.26 Selective extraction of metal cations by pillar[5]arenes with 10 phosphine oxide (H5.26) and 10 diglycoamide arms (H5.27).

Several studies on the use of phosphonium ionic liquids for selective extraction of metal cations from aqueous solution were reported. Binnemans and co-workers described a green extraction process in which cobalt was separated as a tetrachlorocobaltate(ii) complex in a tri(he yl)tetradecylphosphonium chloride ionic liquid phase. This left behind nickel, magnesium and calcium in the aqueous phase. The overall process showed a vety low environmental impact since no additional organic solvents were required. Other processes to extract zinc(n) nickel(II) and cobalt(II), cadmium (11), palladium and... 

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