Separation inorganic sorbents

For the extraction of Tc from molybdemun irradiated by neutrons or separated from uranium fission products, inorganic sorbents, especially aliuninum oxide have widely been applied. In preparing a Tc generator from irradiated molybdenum , MoOj is dissolved in cone, nitric acid, the solution is diluted and passed through an aluminum oxide column. The column is then eluted by 0.2 N H2SO4 to extract Tc. If molybdenum is adsorbed by AljOj as molybdatophos-phate instead of molybdate, the exchange capacity of molybdenum increases from... 

The number of publications involved with the recovery of rubidium from seawater is very limited. Most of the work in this field is by Russian scientists, who have proposed several schemes for the combined recovery of rubidium, strontium, and potassium with natural zeolites [15, 19, 250-253, 257]. A number of inorganic sorbents with high selectivity toward rubidium were also synthesized for the recovery of rubidium from natural hydromineral sources, including seawater. Ferrocyanides of the transition-metal ions were shown to exhibit the best properties for this purpose [258, 259]. Mordenite (another natural zeolite) has recently been proposed for selective recovery of rubidium from natural hydromineral sources as well [260]. A review of the properties of inorganic sorbents applicable for the recovery of rubidium from hydromineral sources has been published [261]. Studies of rubidium recovery fix>m seawater [15, 19, 250-253] have shown that the final processing of rubidium concentrates, especially the selective separation of Rb -K mixtures remains the major problem. A report was recently published showing that this problem can be successfully solved by countercurrent ion exchange on phenolic resins [262]. 

The RO process was implemented at the Institute of Atomic Energy, Swierk. The wastes collected there, from all users of nuclear materials in Poland, have to be processed before safe disposal. Until 1990 the wastes were treated by chemical methods that sometimes did not ensure sufficient decontamination. To reach the discharge standards the system of radioactive waste treatment was modernized. A new evaporator integrated with membrane installation replaced old technology based on chemical precipitation with sorption on inorganic sorbents. Two installations, EV and 3RO, can operate simultaneously or separately. The membrane plant is applied for initial concentration of the waste before the evaporator. It may be also used for final cleaning of the distillate, depending on actual needs. The need for additional distillate purification is necessitated due to entrainment of radionuclides with droplets or with the volatile radioactive compounds, which are carried over. 

Application of Inorganic Sorbents in Actinide Separations Processes... 

For several good reasons - poor hydraulic behavior, unsatisfactory sorption kinetics, unavailability, in some cases, of commercial quantities, etc., - inorganic sorbents, in contrast to their organic counterparts, have not been used extensively in the backend of the nuclear fuel cycle. Also, such production-scale applications of inorganic exchangers as have been made have been concerned much more with sorption of particular fission products (e.g., 137Cs) than with separation or purification of actinides. 

Various other inorganic sorbents are used occasionally in TLC for rather specific separation problems. These sorbents are generally unavailable as precoated plates and must be prepared from aqueous or alcoholic slurries. For further details, see Rossler (1969). Magnesium oxide layers were developed with petroleum ether (30-50°C)-benzene (3 1) for the separation and quantification of alpha- and beta-carotene in lettuce and snails (Drescher et al., 1993). Zinc carbonate with a starch binder has been used to separate aldehydes, ketones, and other carbonyl groups (Rossler, 1969). Magnesium silicate (talc or Florisil) prepared as an alcoholic slurry has been used, to separate pesticides (Getz and Wheeler, 1968), fatty acids, and lanatosides (Rossler, 1969). Charcoal has been combined with silica gel for ketone separations (Rossler, 1969). Two forms of charcoal are available, polar and nonpolar, and each type has very different capabilities. Charcoal has had very limited use in TLC, partly because of the difficulty of zone detection on the layer. For a discussion of the adsorptive properties of charcoal, see Snyder (1975). 

Polar inorganic sorbents. TLC on tradi tional straight phases such as alumina and silica is still the method of choice for many separation problems. Especially for separation of organic-soluble compounds such as lipophilic vitamins straight phase 11.C remains very successful. This is also demonstrated by the large number of applications on polar inorganic non-modified sorbents. 

Eor a long time there have been discussions about which type of sorbent is the best for SEC separations in various mobile phases. In principle, organic (copolymer) and inorganic packings can be used. Each type of packing has its benefits and drawbacks. Table 9.3 summarizes major sorbent properties and reveals some interesting aspects of SEC separations and its requirements on packings. 

The following sorbents have proven useful for the adsorptive separation of volatile inorganic species.1... 

Sorbents for the Separation of Volatile Inorganic Species Separation Material Typical Separations... 

Y.-K. Lu and X.-P. Yan, An imprinted organic-inorganic hybrid sorbent for selective separation of cadmium from aqueous solution, Anal. Chem. 76, 453-457 (2004). 

The columns used for the separation of phenolic acids are mainly reversed phase (RP), other sihca-based chemically bound phases, and non-silica polymers or mixed inorganic-organic phases. Special silica sorbents with reduced metallic residue contents and minimum residual silanol groups on the surface could positively influence peak symmetry without the strict demands for the successful separation of acidic analytes. Almost exclusively, RP C18 phases ranging from 100 to 250 mm in length and usually with an internal diameter of 3.9 to 4.6 mm are recommended. Particle sizes are in the range of 3-10 pm. Short 50- 100-mm columns with 3-pm particles have also been tested for fast phenolic acid separations. Narrow bore columns (internal diameter 2 mm) are recommended especially for HPLC-MS applications.Some problems could arise with the applications of narrow or microbore columns in the direct injections of plant extracts there is the possibility of plugging the column after repeated injections. In these cases, an additional clean-up step has to be applied instead of just the simple extraction... 

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