Leaching continuous

Polymer-supported catalysts incorporating organometaUic complexes also behave in much the same way as their soluble analogues (28). Extensive research has been done in attempts to develop supported rhodium complex catalysts for olefin hydroformylation and methanol carbonylation, but the effort has not been commercially successful. The difficulty is that the polymer-supported catalysts are not sufftciendy stable the valuable metal is continuously leached into the product stream (28). Consequendy, the soHd catalysts fail to eliminate the problems of corrosion and catalyst recovery and recycle that are characteristic of solution catalysis. 

Impeller-agitated tanks These can be operated as continuous leaching tanks, singly or in a series. If the sohds feed is a mixture of particles of different setthng velocities and if it is desirable that all particles reside in the leaching tank the same lengths of time, design of a continuous stirred leach tank is difficult and uncertain. 

Screw-Conveyor Extractors One type of continuous leaching equipment, employing the screw-conveyor principle, is strictly speaking neither a percolator nor a dispersed-solids extractor. Although it is often classed with percolators, there can be sufficient agitation of the solids during their conveyance by the screw that the action differs from an orthodox percolation. 

Figure 24. Drawing of the continuous leaching model used by Vigier et al. (2001) to estimate the residence time of particles in the soils of the Mackenzie Basin, and the related equations. This model assumes that particles are continuously leached in the soil before leaving to the river. Dissolved load of the river integrates the present leaching of the whole soil profile. 238, 234, 230 and 226 are the leaching coefficients of h and Tla nuclides, respectively, and x is the duration of the chentical...

Supercritical fluid extraction can be performed in a static system with the attainment of a steady-state equilibrium or in a continuous leaching mode (dynamic mode) for which equilibrium is unlikely to be obtained (257,260). In most instances the dynamic approach has been preferred, although the selection of the method probably depends just as much on the properties of the matrix as those of the analyte. The potential for saturation of a component with limited solubility in a static solvent pool may hinder complete recovery of the analyte. In a dynamic system, the analyte is continuously exposed to a fresh stream of solvent, increasing the rate of extraction from the matrix. In a static systea... 

Figure 10.5. Flow diagram for continuous leaching plant...

The continuous leaching procedure (a minicolumn packed with a chelating resin) and concentration step were established using the experimental design... 

The experimental conditions influencing an ultrasound-assisted continuous leaching process were studied using an experimental design... 

Figure 2. One-pass continuous leaching system—functional diagram...

In continuous manifolds (particularly flow injection manifolds), the word open is used to refer to those cases where the entire light or diameter of the tubing is occupied by liquids by contrast, packed is used when the solid material (a sorbent, a support-enzyme conjugate, etc.) fills a portion of the tube. In the context of continuous leaching manifolds, open as opposed to closed is used to distinguish linear manifolds from manifolds in which the liquid is recirculated with the aid of valves that convert the manifold from closed to open and vice versa. 

This has been achieved by (a) reduction with 4 M mercaptoethanol (Thompson and O Donnell, 1961,1962b), (b) using 0.1 M benzyl mercaptan in ethanol-water mixture (Maclaren, 1962), (c) electrolytic reduction at a constant cathode potential, using catalytic concentrations of thioglycolate maintained in the SH form continuously (Leach et al., unpublished observations, 1963), and (d) repeated reduction and alkylation of the SH groups of the wool (O Donnell, 1954). 

Continuous leaching can also be carried out on a laboratory scale, with one or more tanks (in series or in parallel) and with recycling of solids, if necessary. The difficulties that arise in long-term operation of these systems are usually due to wear on the equipment due to the action of the mineral particles, problems in maintaining complete suspension and homogeneity of the mineral, and accurate transfer of relatively small volumes of mineral suspensions from the feed tank to the... 

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