Separation selective resins

Kiss [8] examined various techniques for the efficient separation and preconcentration of boron from marine sediments. Alkaline fusion with potassium carbonate was used to render boron reactive, even in the most resistant silicate minerals. Fusion cakes were extracted with water and borate was isolated by Amberlite XE-243 boron-selective resin. Borate was determined spectrophotometrically, following elution with 2 mol L 1 hydrochloric acid. Either the carminic acid complex (620nm), formed in sulphuric acid (94%) or sulphuric acetic acid (1 4), or the azomethine hydrogen ion association complex (415nm) formed at pH5.2, were used for borate measurement. 

Carbon molecular sieve membranes. Molecular sieve carbons can be produced by controlled pyrolysis of selected polymers as mentioned in 3.2.7 Pyrolysis. Carbon molecular sieves with a mean pore diameter from 025 to 1 nm are known to have high separation selectivities for molecules differing by as little as 0.02 nm in critical dimensions. Besides the separation properties, these amorphous materials with more or less regular pore structures may also provide catalytic properties. Carbon molecular sieve membranes in sheet and hollow fiber (with a fiber outer diameter of 5 pm to 1 mm) forms can be derived from cellulose and its derivatives, certain acrylics, peach-tar mesophase or certain thermosetting polymers such as phenolic resins and oxidized polyacrylonitrile by pyrolysis in an inert atmosphere [Koresh and Soffer, 1983 Soffer et al., 1987 Murphy, 1988]. 

Separation by ion exchange Strongly basic or weakly basic ion exchange resins are used to separate selectively the uranium from the weakly acidic or alkaline solutions from the leaching step. The uranium is eluted from the ion exchange resins with nitrate or chloride solutions as anionic (carbonato- or sulfato-) complexes. 

Even more advantageous is the fact that with the concentration of the feed mixture increasing, the distance between the fronts of the two components under separation noticeably increases. This corresponds to an increase in the separation selectivity, which further enhances the productivity of the process. An analogous phenomenon was first observed by Nelson and Kraus [116] in 1958 in the separation of concentrated solutions of LiCl from HCl on the anion-exchange resin Dowex-lxlO. The prolonged retention of HCl at increasing LiCl concentration was explained at that time by the authors as due to a drop of the activity coefficient of HCl in the resin phase (which, obviously, was not a correct explanation). 

Pertechnetate separation is acconqilished using a strongly basic anion exchange resin. The separation selectivity using anion exchange is adequate for the analysis of aged LAW sanqile matrixes and provides reliable separation of pertechnetate from the major radioactive constituents ( Sr/ V, Cs) and the minor constituents (e.g., isotopes of Sn, Sb, and Ru). A combination of column washes using dilute nitric acid, nitric-oxalic acid, sodium hydroxide, and moderately concentrated nitric acid has been developed for reliable separation of pertechnetate from anionic species. 

The selectivity of the present LIX79 impregnated resins against the extraction of different metal-cyano complexes was studied with a 35% LIX 79 content resin and aqueous solutions with aqueous 10 mg/L metal concentration. Results are plotted in Figure 9.13, which represents the percentage of metal extraction by TVEX/LIX 79 resins against equilibrium pH, showed that the aurocyanide complex is extracted at the most alkaline pH value and, consequently, can be separated selectively from other metal-cyano complexes present in the aqueous phase in this pH range. 

SPE is one of the most important preconcentration/separation procedures to trace heavy-metal ions and organic pollutants, due to its simplicity and limited usage of the organic solvents. Among many others, ion exchange and selective resins are very popular methods due to their applicability to both preconcentration and separation. The implementation of highly selective columns to flow-based methodologies allowed the automation of many analytical methods. 

Separation by extraction chromatographic materials appears as the most suitable technique to develop automated radiochemical methodologies followed by LLE. There are a large number of selective resins for radionuclides determination, e.g. Ra, Ni, Pb, Th, U, Np, Pu, Am, Cm, Sr, Tc, H, Fe and Pa [4], which have been largely included in protocols with online separation [5—8]. Automatic separation exploiting flow systems can also be carried out by LLE which involves the formation of complexes between several organic compounds and radionuclides [9—11]. 

Selective resins for radionuclide separations are commercially available in different forms, such as cartridges, packed columns, beads and disks. Moreover, there are available various pore size ranges. 

Polymeric cation-exchange resins are also used in the separation of fmctose from glucose. The UOP Sarex process has employed both 2eohtic and polymeric resin adsorbents for the production of high fmctose com symp (HFCS). The operating characteristics of these two adsorbents are substantially different and have been compared in terms of fundamental characteristics such as capacity, selectivity, and adsorption kinetics (51). 

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