Particle separation from solution,

Coa.cerva.tlon, A phenomenon associated with coUoids wherein dispersed particles separate from solution to form a second Hquid phase is termed coacervation. Gelatin solutions form coacervates with the addition of salt such as sodium sulfate [7757-82-6] especially at pH below the isoionic point. In addition, gelatin solutions coacervate with solutions of oppositely charged polymers or macromolecules such as acacia. This property is useful for microencapsulation and photographic apphcations (56—61). 

Coacervation. A phenomenon associated with colloids wherein dispersed particles separate from solution to form a second liquid phase is termed... 

The spin coating technique of preparing PAMAM dendrimer samples for AFM is the best method to maintain undistorted dendrimer shape allows the visualization of isolated single dendrimer molecules. In spin coating, a dendrimer solution is rapidly spread across the sample surface and the majority of particles separate from one another. 

It is not obvious to all scientists that the pH reported in (pH) or ao(pH) plots (from which the lEP or PZC is determined) is the equilibrium pH of the dispersion used for the measurements. The following description was found in [208], The authors equilibrated their particles in a solution 1 of pH 1, 1.9, 3, 5, 7, 8, 11, or 13. The particles were then separated from solution 1 and redispersed in pure water. The new dispersion (particles in solution 2) was used to measure the electrophoretic mobility. Obviously, the pH of the solution 2 formed by equilibration of pretreated particles with water was different from the pH of solution 1, and most scientists would have plotted the potential against the pH of solution 2 to... 

An important means by which small particles in suspension are separated from solutions is through capture by collectors, which may be larger particles, or granular, porous, or fibrous media. An example of such collection is filtration. The separated solids may be collected as a cake on the surface of the filter medium (much like ultrafiltration), and this is termed cake filtration. Alternatively, the solids may be retained within the pores of the medium, and this is termed depth filtration. It is important to recognize that particle collection in a porous medium is not simply a matter of straining that is, the capture is not purely steric, since, in filtration, particles are captured that are much smaller than pores of the medium. The capture of small suspended particles from fluids in laminar flow by a collector is a consequence of the simultaneous action of fluid mechanical forces and forces between the particle and collector, such as van der Waals or electrostatic forces. It is the combined forces, at least close to the collector, that govern the particle trajectories and determine whether a particle will be transported to and retained at the surface of a collector that is fixed in the flow (Spielman 1977). 

We can consider the solution process as having three components, each with an associated enthalpy change Solute particles separate from one another (AHsoiute)> solvent particles separate from one another ( Hgolventh solute and solvent particles mix (AHj ). The overall enthalpy change, AHsoln> is... 

Step 1. Solute particles separate from each other. This step involves overcoming intermolecular attractions, so it is endothermic ... 

The principle of this technique is similar to conventional liquid antisolvent crystallization. The high solubility of SCFs, which is an antisolvent for the solute, in most common organic solvents causes a volume expansion and a subsequent decrease in the solvent density by nearly twofold (8). Such a reduction in the solvent capacity causes phase changes wherein the solute molecules nucleate and particles separate from the solution. The process is typically carried out... 

So far, we have been concerned with the distribution of molecules, ions or macromolecules between two immiscible phases. The molecules may have been solutes present in small quantities or major constituents of either or both phases. Classical principles of thermodynamics were used to develop estimates of such solute distributions. When it comes to large particles, such as ore fines, cells or other particulate matter, classical thermodynamics may not appear to he of any use. However, using the phenomenon of wetting based on interfecial thermodynamics, particle separation from one phase is achieved by introducing a second immiscible phase. 

Suspensions contain particles with different densities. When particles are larger than about lOOOmn in diameter, they can separate from solution upon standing. 

Electrospun nanoflbrous membranes (ENMs) were found to be applicable for particle separation from water. Thus, they can be used for the treatment of wastewater prior to the treatment by UF, NF, and RO [56,59-72], Gopal et al. [73] demonstrated the PVDF ENM applicability in particulate removal. Characterization of these electrospun membranes revealed that they have similar properties to that of conventional MF membranes. The electrospun membranes were used to separate 1, 5, and 10 pm PS particles. The electrospun membranes were successful in rejecting more than 90% of the microparticles from solution. It was suggested by Gopal et al. that nanoflbrous membranes have potential for the pretreatment of water prior to RO or as prefllters to minimize fouling and contamination prior to UF or NF. 

Two classes of micron-sized stationary phases have been encountered in this section silica particles and cross-linked polymer resin beads. Both materials are porous, with pore sizes ranging from approximately 50 to 4000 A for silica particles and from 50 to 1,000,000 A for divinylbenzene cross-linked polystyrene resins. In size-exclusion chromatography, also called molecular-exclusion or gel-permeation chromatography, separation is based on the solute s ability to enter into the pores of the column packing. Smaller solutes spend proportionally more time within the pores and, consequently, take longer to elute from the column. 

Moving-bed percolation systems are used for extraction from many types of ceUular particles such as seeds, beans, and peanuts (see Nuts). In most of these cases organic solvents are used to extract the oils from the particles. Pre-treatment of the seed or nut is usually necessary to increase the number of ceUs exposed to the solvent by increasing the specific surface by flaking or rolling. The oil-rich solvent (or misceUa) solution often contains a small proportion of fine particles which must be removed, as weU as the oil separated from the solvent after leaching. 

In contrast to sodium chloride, langbeinite has an extremely slow rate of solution. Upon control of agitation time, essentially all the sodium chloride dissolves but most of the langbeinite remains as a soHd. Langbeinite is separated from the brine, dried, and then screened into granular, standard, and special-standard particle sizes. These fractions are marketed directiy. In one plant, the unsalable fines are used as the source of sulfate reactant for the production of potassium sulfate. 

Sorption and Desorption Processes. Sorption is a generalized term that refers to surface-induced removal of the pesticide from solution it is the attraction and accumulation of pesticide at the sod—water or sod—air interface, resulting in molecular layers on the surface of sod particles. Experimentally, sorption is characterized by the loss of pesticide from the sod solution, making it almost impossible to distinguish between sorption in which molecular layers form on sod particle surfaces, precipitation in which either a separate soHd phase forms on soHd surfaces, covalent bonding with the sod particle surface, or absorption into sod particles or organisms. Sorption is generally considered a reversible equdibrium process. 

Extraction of Bertrandite. Bertrandite-containing tuff from the Spor Mountain deposits is wet milled to provide a thixotropic, pumpable slurry of below 840 p.m (—20 mesh) particles. This slurry is leached with sulfuric acid at temperatures near the boiling point. The resulting beryUium sulfate [13510-49-1] solution is separated from unreacted soflds by countercurrent decantation thickener operations. The solution contains 0.4—0.7 g/L Be, 4.7 g/L Al, 3—5 g/L Mg, and 1.5 g/L Fe, plus minor impurities including uranium [7440-61-1/, rare earths, zirconium [7440-67-7] titanium [7440-32-6] and zinc [7440-66-6]. Water conservation practices are essential in semiarid Utah, so the wash water introduced in the countercurrent decantation separation of beryUium solutions from soflds is utilized in the wet milling operation. 

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