Particle separation methods

Particle separation methods can be divided into two groups (a) those that use gravity or centrifugal force, in which the particles move relative to the suspending medium (b) those that use chromatographic principles, where the particles move with the same velocity as the fluid. 

In the case of the LIST method, the curve of particle concentration versus sedimentation time of the particles passing the detector (at a given position) represents a differential PSD. The relationship between the (spherical) particle diameter, d, and the time, t, required for it to move from the meniscus to the detector, in the absence of a density gradient, is given by Stokes law, 

The intensity signal produced by the detector does not provide a direct measurement of the particle concentration, as it also depends on the particle mass and, in the case of light extinction, on the particle size itself. The signal can be related to the particle concentration using the theory of electromagnetic waves and particle interactions. The intensity, I, transmitted by a uniform dispersion illuminated by monochromatic light of intensity Iq is given by Beer s law. 

Using this optical correction, obtained from S/Qext, an accurate PSD can be obtained. 

A known quantity of concentrated sample suspension is diluted sufficiently so that particles in a given size range pass individually through the active sensing zone of the sensor, thereby 

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The scope of coverage includes internal flows of Newtonian and non-Newtonian incompressible fluids, adiabatic and isothermal compressible flows (up to sonic or choking conditions), two-phase (gas-liquid, solid-liquid, and gas-solid) flows, external flows (e.g., drag), and flow in porous media. Applications include dimensional analysis and scale-up, piping systems with fittings for Newtonian and non-Newtonian fluids (for unknown driving force, unknown flow rate, unknown diameter, or most economical diameter), compressible pipe flows up to choked flow, flow measurement and control, pumps, compressors, fluid-particle separation methods (e.g.,... 

Particle separation methods based on the effects on suspended particles of exposure to an ultrasonic standing-wave field have been reported [51]. Carrier medium exchange in a laminar flow microchannel has also been achieved using... 

This is an introductory textbook for studying separation. Primarily, this book covers the separation of mixtures of molecules in addition, it provides a significant treatment of particle separation methods. Separation of macromolecules has also received some attention. The treatment and coverage of topics are suitable for chemical engineering students at undergraduate and graduate levels. There is enough material here to cover a variety of introductory courses on separation processes at different levels. 

Virtually all separation processes taught to chemical engineering students in a variety of courses have heen covered via the approach illustrated in Chapters 3, 4, 6, 7 and 8 in addition, many particle separation methods have been treated. The structural similarity in the separation method between apparently unrelated separation processes becomes quite clear. A few basic principles equip the students with the capability to understand a wide variety of separation processes and techniques, including emerging ones. To aid the student, there are 118 worked examples, 300 problems, 340 figures, 100 tables and 1011... 

A separation method in which a mixture passes through a bed of porous particles, with smaller particles taking longer to pass through the bed due to their ability to move into the porous structure. 

SI units stands for Systeme International d Unites. These are the internationally agreed on units for measurements, (p. 12) size-exclusion chromatography a separation method in which a mixture passes through a bed of porous particles, with smaller particles taking longer to pass through the bed due to their ability to move into the porous structure, (p. 206)... 

It is worth noting that some of these methods are both an inlet system to the mass spectrometer and an ion source at the same time and are not used with conventional ion sources. Thus, with electrospray, the process of removing the liquid phase from the column eluant also produces ions of any emerging mixture components, and these are passed straight to the mass spectrometer analyzer no separate ion source is needed. The particle beam method is different in that the liquid phase is removed, and any residual mixture components are passed into a conventional ion source (often electron ionization). 

Size reduction (qv) or comminution is the first and very important step in the processing of most minerals (2,6,10,20—24). It also involves large expenditures for heavy equipment, energy, operation, and maintenance. Size reduction is necessary because the value minerals are intimately associated with gangue and need to be Hberated, and/or because most minerals processing/separation methods require the ore mass to be of certain size and/or shape. Size reduction is also required in the case of quarry products to produce material of controlled particle size (see Size measurement of particles). In some instances, hberation of valuables or impurities from the ore matrix is achieved without any apparent size reduction. Scmbbers and attritors used in the industrial minerals plants, eg, phosphate, mtile, glass sands, or clay, ate examples. 

Solids separation based on density loses its effectiveness as the particle size decreases. For particles below 100 microns, separation methods make use of differences in the magnetic susceptibility (magnetic separation), elec trical conductivity (electrostatic separation), and in the surface wettability (flotation and selec tive flocculation). Treatment of ultrafine solids, say smaller than 10 microns can also be achieved by utilizing differences in dielectric and electrophoretic properties of the particles. 

Modes of Operation There is a close analogy between sedimentation of particles or macromolecules in a gravitational field and their elec trophoretic movement in an electric field. Both types of separation have proved valuable not only for analysis of colloids but also for preparative work, at least in the laboratoiy. Electrophoresis is applicable also for separating mixtures of simple cations or anions in certain cases in which other separating methods are ineffectual. 

A more flexible option from an operational viewpoint is the implementation of process-oriented enhancements that intensify particle separation. This can be achieved by two different methods. In the first method, the suspension to be separated is pretreated to obtain a cake with minimal resistance. This involves the addition of filter aids, flocculants or electrolytes to the suspension. In the second method, the period during which suspensions are formed provides the opportunity to alter suspension properties or conditions that are more favorable to... 

Filter aids may be applied in one of two ways. The first method involves the use of a precoat filter aid, which can be applied as a thin layer over the filter before the suspension is pumped to the apparatus. A precoat prevents fine suspension particles from becoming so entangled in the filter medium that its resistance becomes exces-sive. In addition it facilitates the removal of filter cake at the end of the filtration cycle. The second application method involves incorporation of a certain amount of the material with the suspension before introducing it to the filter. The addition of filter aids increases the porosity of the sludge, decreases its compressibility, and reduces the resistance of the cake. In some cases the filter aid displays an adsorption action, which results in particle separation of sizes down to 0.1 /i. The adsorption ability of certain filter aids, such as bleached earth and activated charcoals, is manifest by a decoloring of the suspension s liquid phase. This practice is widely used for treating fats and oils. The properties of these additives are determined by the characteristics... 

Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

Gelatin and albumin nanoparticles have been prepared through desolvation of the dissolved macromolecules by either salts (e.g., sodium sulfate or ammonium sulfate) or ethanol [179-182], This is, in principle, similar to a simple coacervation method. The particles can then be insolubilized through cross-linking with an optimum amount of aldehydes. These phase separation methods avoid the use of oils as the external phase. 

The physical separation methods find wide application in this industry because of the nature of the wastes. Centrifugation may be feasible in some applications, but it is not suitable for abrasive or very fine particles (less than 5 pm). 

Flotation. In many cases, contaminants adsorbed on the surface of clay particles, or contaminants occurring in soil as discriminate particles, have different surface properties to clean soil particles. By adding special chemical substances, the formation of a hydrophobic surface on the contaminated particles is possible. Pulp aeration results in the attachment of hydrophobic contaminated particles to the surface of the small bubbles that are formed. In this way, selective flotation of these particles is achieved. Contrary to the gravimetric separation methods, flotation offers the possibility to separate contaminated and noncontaminated particles of the same grain size and density but with different surface properties. 

A second separation process reported by EBC is based on the use of hydrocyclones. Stable emulsions formed by good oil-cell-water contact and mixing can be separated continuously with hydrocyclones to obtain relatively clean oil and water. A method and an apparatus for separating a water/organic/solid emulsion, wherein the solid comprises particles having a length of about 50 xm or less, has been disclosed [267], This separation process scheme is shown in Fig. 14 and as before the separation method is envisioned as part of a BDS process. 

An emulsion separation method using hydrocyclones. The emulsion comprises a continuous phase, a discontinuous phase and fine solid particles. In the first step, the original emulsion is separated into an overflow emulsion and an underflow emulsion, in a first hydrocyclone. The overflow emulsion comprises portions of the continuous phase, the discontinuous phase and the fine solid particles. The overflow emulsion is inverted in which the continuous phase of the overflow emulsion is now a second discontinuous phase and the original discontinuous phase becomes a second continuous phase. Then, the inverted emulsion is directed to one or more subsequent hydrocyclones and the second continuous and discontinuous phases are collected. The fine solid particles remain in the second discontinuous phase. 

A molecule carried along in the mobile phase must contact the stationary phase if the system is an equilibrium separation method. That means that a molecule moving between particles must sense the chemical potential in the direction of the stationary phase and move toward it. 

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