Solid-liquid separators selection

Clark, J. G., Select the Right Fabric for Liquid-Solid Separation, Chem. Eng. Prog., V. 86, No. 11, 1990. 

Table 2.3-1 lists each potential arsenic removal process evaluated in this study along with major evaluation criteria with respect to HP s GaAs processing facility. Because effective liquid solid separation was required, filtration was selected as the process of choice. 

Chapter 5 focuses on equipment for the separation of heterogeneous phases. The chapter starts with a convenient general selection guide. More specific guides are given for liquid-solid separations, Section 5.5, and for sohd-sohd separations. Section 5.18. 

Clark, J. G. 1990. Select the right fabric for liquid-solid separation. Chemical Engineering Progress 86 45-50. 

A major problem in the treatment of nonaqueous systems is the removal of eolloidal particles to produce acceptable liquid products (e.g., fuel oil). Such a situation is encountered in hydrocarbon production from tar sands and oil shale. The particles (such as oxides, silicates, and clay mineral) suspended in the hydrocarbon hquids originate from a rock matrix. Particle separation problems occur in the solvent extraction of bitumen with nonaqueous media such as toluene. Electrostatic forces (bonding forces) play a predominant role in the physical state of these nonaqueous systems. In many instances, by addition of antisolvents, and selecting the proper temperature and agitation, these systems can be altered to improve solid separation. Separation of carbon black particles suspended in tetralin using Aerosol OT as a surfactant and by filtration through a bed of sand (deep-bed filtration) is another example of liquid-solids separation in nonaqueous systems. 

Roasting can be used instead of pressure leaching to regenerate the copper sulfate solution in Step 3. If roasting is selected, batch centrifugation instead of decantation is required to concentrate the copper sulfide slurry to effect a cleaner liquid-solids separation. Step 4, copper recovery, can also be accomplished by ion exchange. 

Conventional downflow sand filters are effective for liquid-solid separation at flow rates up to about 15m /h.m of filter area, although higher rate downflow filters are available. With proper selection of filter media, gelatinous as well as granular suspended matter can be filtered out, without a rapid differential pressure build-up. 

One application of the grand canonical Monte Carlo simulation method is in the study ol adsorption and transport of fluids through porous solids. Mixtures of gases or liquids ca separated by the selective adsorption of one component in an appropriate porous mate The efficacy of the separation depends to a large extent upon the ability of the materit adsorb one component in the mixture much more strongly than the other component, separation may be performed over a range of temperatures and so it is useful to be to predict the adsorption isotherms of the mixtures. 

Certain highly porous solid materials selectively adsorb certain molecules. Examples are silica gel for separation of aromatics from other hydrocarbons, and activated charcoal for removing liquid components from gases. Adsorption is analogous to absorption, but the principles are different. Layers of adsorbed material, only a few molecules thick, are formed on the extensive interior area of the adsorbent - possibly as large as 50,000 sq. ft./lb of material. 

For future studies on MOF-based slurry systems, there is basic selection of criteria that needs to be satisfied by both MOF and the liquid solution. The selection of the MOF possessing the appropriate pore size for the preparation of the slurry system is very important to guarantee that the size of the liquid is large enough and does not occupy the pores which leaves no space for C02 to adsorb. Moreover, the structural stability of the MOF in the aqueous solution is essential so that it does not lose its porous framework nor its surface area. The selection of the liquid candidate is crucial, as it should not provide any extra mass transfer resistance for C02 molecules. Further, experimental and computational investigations are still required to understand the separation mechanism in slurry mixtures and to have insight into the different types of interactions between the gas, liquid, and solid materials. 

Selective transfer of material in sub-microgram to milligram quantities between a solid sorbent and a liquid phase separations depend on different relative affinities for the two phases based on adsorption, size or charge selectivity achieved by pH control, solvent composition and surface chemistry of the sorbent. 

Solid phase extraction (SPE) involves the separation of components of samples in solution through their selective interaction with and retention by a solid, particulate sorbent. SPE depends on differences in the affinities of the various components of the sample for the sorbent. The mechanisms of the interactions are virtually identical to the sorption processes that form the basis of liquid chromatographic separations (p. 80). The choice of solvent, the pH and ionic strength of aqueous solutions, and the chemical nature of the sorbent surface, especially its polarity, are all of importance in controlling the selectivity and efficiency of an extraction. 

On the basis of the preceding discussion, it should be obvious that ultratrace elemental analysis can be performed without any major problems by atomic spectroscopy. A major disadvantage with elemental analysis is that it does not provide information on element speciation. Speciation has major significance since it can define whether the element can become bioavailable. For example, complexed iron will be metabolized more readily than unbound iron and the measure of total iron in the sample will not discriminate between the available and nonavailable forms. There are many other similar examples and analytical procedures that must be developed which will enable elemental speciation to be performed. Liquid chromatographic procedures (either ion-exchange, ion-pair, liquid-solid, or liquid-liquid chromatography) are the best methods to speciate samples since they can separate solutes on the basis of a number of parameters. Chromatographic separation can be used as part of the sample preparation step and the column effluent can be monitored with atomic spectroscopy. This mode of operation combines the excellent separation characteristics with the element selectivity of atomic spectroscopy. AAS with a flame as the atom reservoir or AES with an inductively coupled plasma have been used successfully to speciate various ultratrace elements. 

In Section 2.5, we described separation procedures in which analytes are extracted from solid samples via contact with liquid solvents that selectively dissolve the analyte and leave other components undissolved or unextracted. There are several methods by which analytes can be extracted from liquid matrices as well. 

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