Filtration of suspensions

Cross-flow-elec trofiltratiou (CF-EF) is the multifunctional separation process which combines the electrophoretic migration present in elec trofiltration with the particle diffusion and radial-migration forces present in cross-flow filtration (CFF) (microfiltration includes cross-flow filtration as one mode of operation in Membrane Separation Processes which appears later in this section) in order to reduce further the formation of filter cake. Cross-flow-electrofiltratiou can even eliminate the formation of filter cake entirely. This process should find application in the filtration of suspensions when there are charged particles as well as a relatively low conduc tivity in the continuous phase. Low conductivity in the continuous phase is necessary in order to minimize the amount of elec trical power necessaiy to sustain the elec tric field. Low-ionic-strength aqueous media and nonaqueous suspending media fulfill this requirement. 

Filtration of suspensions, e.g. in filter presses, rotary vaeuum filters Sedimentation, gravity settling... 

Experimental evidence has demonstrated that Dean vortices can be effective for enhancement of membrane performance under laminar conditions [18]. As flow conditions approach the transition and turbulent flow regimes, straight membranes have a better mass transfer and higher wall shear rate than in flows with curved membrane channels. The effects of Dean vortices on the performance of membrane filtration have been studied experimentally and theoretically by Belfort and coworkers [19-22]. Mallubhotla and Belfort [21] assessed the filtration of suspensions of polydispersed polystyrene particles (mean diameter 25 pm) and silica particles (mean diameter 20 pm) with and without the presence of Dean flow using an 180° U-bend channel... 

Particle size increases from 100 up to 500 A at use of the mixed catalyst and the increase in density of films is observed. A filtration of suspension it is possible to receive films of any sizes. On the various substrates possessing good adhesive properties, it is possible to receive films dispersion of gel. Polymer easily doping AsF5, FeCl3,l2, and other electron acceptors. Preliminary tests have shown some advantages of such materials at their use in accumulators [48]. Gels poly acetylene with the similar properties. 

Cake filtration is based on passing a suspension through a permeable, relatively thin medium (chapter 8). The sohds are deposited in the form of a cake on the upstream side of the medium. As soon as the first layer of cake is formed, the subsequent filtration takes place on top of this cake and the medium provides only a supporting function. These so-called surface filters are best used for filtration of suspensions of solids concentrations in excess of 1% by volume in order to minimize medium blinding which occurs in the filtration of dilute suspensions. If cake filtration is to be applied to clarification of liquids, which imphes low feed concentrations of sohds, addition of filter aids is usually necessary—see section 2.2. 

Recovery of the collected material from the rotating chamber of the centrifuge and its further treatment, e.g., splitting into subsamples, washing for removal of seasalt or filtration of suspensions for sample transfer, should be performed in a dust-free environment (clean room or clean bench). 

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