Bulk effects, separation

One possible application in which large amounts of rare earths and actinides would be processed occurs in some schemes for nuclear waste management. If it should prove to be advantageous to remove transplutonium elements from nuclear waste, for example, the recovery of Am and Cm from the much larger amounts of rare earths would be required. This problem has been investigated by the author in tracer tests with rare earth mixtures typical of fission products, using a heavy rare earth such as holmium as a stand-in for Am and Cm (Fig. 5). It is clear that the bulk of the holmium can be recovered in reasonable purity, and that the bulk of the lighter rare earths is effectively separated from the very small amount of heavy rare earths, Am, and Cm. 

Since the probability of the initial recombination can be expressed by the separation step rates, the natural way of its determination is to measure the bulk-generated photocurrent. However, one should keep in mind that the measured photocurrent contains carrier mobilities in addition to the effective separation probability (f/oG). The carrier mobilities... 

The last strategy is the use of supramolecular binding in catalyst immobilization. Immobilization of efficient homogeneous catalysts has been investigated extensively. Except for one case, the thousands of publications and patents have not led to industrial applications. In the s)m-thesis of fine chemicals, homogeneous catalysts may be removed in a column, but crystallization of the product is the preferred operation. In bulk chemical s)mthesis, we find all the unit operations applied to effect separation of the catalyst from the product mixture. 

A crucial factor in chromatographic MIP applications is the extensive peak broadening and tailing that results from the bulk effect in the polymer matrix. This is a critical limitation for MIPs in chromatography. Bulk effects are essential in sensory applications, where the sensitivity of sensor coatings depends on a one-step enrichment for an applicable selective incorporation. Instead, chromatographic columns have thousands of plates for an entire separation and hence the inclusion process can be weaker and less selective in comparison to sensor layers. 

Char acts as a vapour cracking catalyst so rapid and effective separation from the pyrolysis product vapours is essential. Cyclones are the usual method of char removal and two are usually provided - the first to remove the bulk of the material and the second to remove as much of the residual fines as possible. However, some fines always pass through the cyclones and collect in the liquid product where they accelerate aging and exacerbate the instability problem, which is described below. 

Table 1 indicates the solids or substances that can be effectively separated by the adsorptive bubble separation process. In general, the light-weight suspended solids, such as fibers, activated sludge, free oil, chemical floes, and fats, can be readily separated by the process in accordance with the physical-chemical bubble attachment mechanism shown in Fig. 1. The colloidal solids, soluble organics, soluble inorganics, and surface-active substances can be separated from the bulk liquid by the bubble separation process after they are converted from colloidal or soluble form into insoluble form (i.e., suspended solids), which can then be floated by gas bubbles. 

The simplest photoelectrochemical cells consist of a semiconductor working electrode and a metal counter electrode, both of which are in contact with a redox electrolyte. In the dark, the potential difference between the two electrodes is zero. The open circuit potential difference between the two electrodes that arises from illumination of the semiconductor electrode is referred to as the photovoltage. When the semiconductor and counter electrode are short circuited, a light induced photocurrent can be measured in the external circuit. These phenomena originate from the effective separation of photogenerated electron-hole pairs in the semiconductor. In conventional photoelectrochemical studies, the interface between the flat surface of a bulk single crystalline semiconductor and the electrolyte is two dimensional, and the electrode is illuminated from the electrolyte side. However, in the last decade, research into the properties of nanoporous semiconductor electrodes interpenetrated by an electrolyte solution has expanded substantially. If a nanocrystalline electrode is prepared as a film on a transparent conducting substrate, it can be illuminated from either side. The obvious differences between a flat (two dimensional) semiconductor/ electrolyte junction and the (three dimensional) interface in a nanoporous electrode justify a separate treatment of the two cases. 

The shape of the adsorption isotherm is clearly affected by the magnitude of the segmental adsorption energy %s defined above. The thermodynamics of the bulk solution also influence the adsorption for polymers in 6 solutions the amount adsorbed is higher and generally this tends to increase continuously with increasing solution concentration. If the solvent quality is worse still, then one may have a very thick adsorbed layer indeed effectively one has bulk phase separation initiated at the surface. This situation is discussed in section 5.3. 

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