Metal ions separation

When the polymer was prepared by the suspension polymerization technique, the product was crosslinked beads of unusually uniform size (see Fig. 16 for SEM picture of the beads) with hydrophobic surface characteristics. This shows that cardanyl acrylate/methacry-late can be used as comonomers-cum-cross-linking agents in vinyl polymerizations. This further gives rise to more opportunities to prepare polymer supports for synthesis particularly for experiments in solid-state peptide synthesis. Polymer supports based on activated acrylates have recently been reported to be useful in supported organic reactions, metal ion separation, etc. [198,199]. Copolymers are expected to give better performance and, hence, coplymers of CA and CM A with methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN) were prepared and characterized [196,197]. 

Horwitz, E. P. Shulz, W. W. Metal Ion Separation and Preconcentration Progress and Opportunities Bond, A. H. Dietz, M. L. Rogers, R. D. Eds., American Chemical Society, 1998. 

Visser, A.E. et al. Metal ion separations in aqueous biphasic systems and room temperature ionic liquids, PhD thesis. University of Alabama, Tuscaloosa, AL, USA, 2002. 

A number of liquid crystalline polyphosphazenes with mesogenic side groups have been prepared (48—50). Polymers with nonlinear optical activity have also been reported (51). Polyphosphazene membranes have been examined for gas, liquid, and metal ion separation, and for filtration (52—54). There is interest in phosphazene—organic copolymers, blends, and interpenetrating polymer networks (IPNs) (55—61) to take advantage of some of the special characteristics of phosphazenes such as flame retardance and low temperature flexibility. A large number of organic polymers with cydophosphazene substituents have been made (62). 

NEW TECHNOLOGIES FOR METAL ION SEPARATIONS POLYETHYLENE GLYCOL BASED-AQUEOUS BIPHASIC SYSTEMS AND AQUEOUS BIPHASIC EXTRACTION CHROMATOGRAPHY Robin D. Rogers and Jianhua Zhang... 

Goken, G. L., Bruening, R. L., Krakowiak, K. E., and Izatt, R. M. (1999) Metal-ion Separations Using SuperLig or AnaLig Materials Encased in Empore Cartridges and Disks, ACS Symposium Series 716, 251-259. 

Vofsi, D. (1967) Metal-ion separation by Eng Chem Proc Des Develop, 6, 231. 

For a solid-state chemist, it is possible to synthesize compounds with polyhedra containing transition-metal ions separated by diamagnetic elements. By cationic substitution, the following arrangements can be obtained ... 

TABLE XXII. Name and Structure of Several Different Types of Extractants Utilized for Metal Ion Separations... 

A new potentially exciting development in this area of extractions concerns the use of different reversed micellar systems in countercurrent extractions of different rare earth metals. A mathematical model was developed in order to help optimize the different parameters of this new mode of extraction (364). This should facilitate the further development and utilization of this approach to metal ion separations. 

A very important finding is that hard cations (e.g., Be2+, Al3+, Ti4+) prefer ligands with hard donor atoms (e.g., F, O, Cl), and soft cations (e.g., Ag+, Cd2+, Tl+) prefer ligands with soft donor atoms (e.g., I, Te, As). This fact has a myriad of applications, because it can be advantageously used for analysis, selective reactions, metal ion separation, removal, recovery, etc. It is an application of the Hard Soft Acid Base (HSAB) principle enunciated by Pearson at the end of the 1960s. 

Examples of the use of synthetic mixed donor macrocycles in heavy metal ion separations are found in the discrimination of silver from lead. A number of studies indicate that the inclusion of sulfur in macrocyclic sequestering agents shifts the discrimination to silver. An example of this is seen with (57) and (58). For the aza-oxa macrocycle (57) the log K is 5.9 for both silver and lead ions, while the thia-incorporated ligand (58) complexes silver more efficiently (log K = 9.9) compared to lead (log K = 5.7). ... 

CE has been widely used for the analysis of metal ions generally with indirect UV detection. A recent volume of J. Chromatography (201 has covered developments and applications. Typically a small amine such as imidazole or benzylamine is added to the buffer to provide the background UV absorbance signal. Low-pH buffers are normally employed to suppress EOF flow and enhance resolution. Selectivity of metal ion separations can be modified (21 ( by the addition of small oiganic acids such as lactic or formic acid. 

Metal ions separation for hydrometallurgical applications has attracted considerable interest. Selective separations of alkali, alkali earth, heavy metal ions, rare earth, precious metals, etc. are studied by many authors using all the above-described techniques. Referenced works in metal separations classified according to the OHLM techniques with types of membrane walls and carriers used are listed in Table 13.6. 

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