Agglomeration in suspension

They are harder compared with pellets produced by powder layering. Their appearance is similar to pellets obtained by fluidized-bed granulation using the so-called rotating fluidized bed. " Owing to the fact that ideally round pellets are desired, several attempts were made to quantify their roundness. " The spherical agglomeration is a completely different method that is employed to develop pellets that are round and uniform in size. In this, particles are agglomerated in suspension. ... 

At certain conditions agglomeration also takes place in turbulently moving liquid suspensions. This is the case if, for example, a small amount of a second liquid is added as a binder. This component must be able to adhere to the solid particles in the suspension but must be immiscible with the suspending liquid. After its addition, spherical agglomerates form during a suitable movement of the liquid. Figure 86(a) to (h) shows schematically apparatuses that were successfully used for agglomeration in suspension. 

Figure 86. Methods used for spherical agglomeration in suspensions , (a) Container with stirrer, (b) container with liquid circulation, (c) inclined disc, (d) horizontal drum, (e) colloid mill , (f) shaking container, (g) vertical mixer, (h) continuous mixer...

Suspensions of oil in water (32), such as lanolin in wool (qv) scouring effluents, are stabilized with emulsifiers to prevent the oil phase from adsorbing onto the membrane. Polymer latices and electrophoretic paint dispersions are stabilized using surface-active agents to reduce particle agglomeration in the gel-polarization layer. 

Small particles are required, to provide a large surface-area-to-mass ratio and for the solid to remain in suspension. Surface absorption of air (oxygen) by the solid, or tlie evolution of combustible gas or vapour on heating, may be a predisposing factor. The presence of moisture reduces the tendency to ignite it also favours agglomeration to produce larger particles. An increase in the proportion of inert solid in particles tends to reduce combustibility. 

Wojcik, J. and Jones, A.G., 1998b. Particle disruption of precipitated CaC03 crystal agglomerates in turbulently agitated suspensions. Chemical Engineering Science, 53, 1097-1101. 

Consider a conductive solution consisting of water with a soluble salt, i.e.-1% NaCl, and a dispersing agent used to prevent agglomeration of particles in suspension. Two electrodes are placed in solution with a non-conducting orifice between them, as shown in 5.10.14, given on the next page ... 

By introducing surfactants, which lower the interfacial tension, it is possible to reduce the work necessary to deflocculate agglomerates. In liquid suspensions the introduction of an interfacial tension depressant facilitates wetting of the solid by the liquid and the displacement of adsorbed gases from the solid surface. Certain solids have adsorbed films whose adhesional forces are so great that they resist all mechanical efforts to displace them. Upon the addition of a surfactant, the Aims are displaced and a solid-liquid interface is achieved (1). 

Chimmili, S., Shear induced agglomeration in particulate suspensions. M. Sci. thesis, West Virginia University (1996). 

In this section three miscellaneous topics in the area of agglomeration shall be discussed, namely, dry pelletization, spherical agglomeration in liquid suspension, and spontaneous or inadvertent agglomeration of fine particles. 

When ultrasound emitter and electrode are different elements in the system, electrode-apart-transducer configuration, Fig. 4.2a, ultrasound removes the nanoparticles from the cathode to form suspended seeds. The ultrasonic agitation maintains a suspension of these preformed nanoparticles, which move continuously around, hit the electrodes, and these charged particles attach to one another and grow in suspension [90]. In this case, ultrasound keeps the larger structures from agglomeration. 

A similar technique has been applied to the generation of monodisperse suspensions in water. This type of method was first used in medical field and then widely used to spray monodisperse solid particles such as polystyrene latex particles. Aerosols of solutes have also been produced by atomizing solutions of salt, sugar or methylene blue dye dissolved in water. In practical operations, a low concentration of solid particles in a solvent is recommended in order to avoid possible agglomeration of suspensions in the solvent. 

Newtonian fluids containing a high concentration of rigid particles can show non-Newtonian flow behaviour with increasing shear rate, due to a break up of agglomerates in the shear field [4]. For many pseudoplastic fluid suspensions the... 

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