Filtration of colloids

Gregory, I., 1984b. Flocculation and filtration of colloidal particles. In Emergent process methods for high temperature ceramics, Eds. R.F. Dvais etai. Plenum Press, London p. 59. 

D. Jiao and M. M. Sharma. Mechanism of cake buildup in crossflow filtration of colloidal suspensions. J Colloid Interface Sci, 162(2) 454-462, February 1994. 

Wen LS, Santschi PH, Tang DG (1997) Interactions between radioactively labeled colloids and natural particles Evidence for colloidal pumping. Geochim Cosmochim Acta 61 2867-2878 Whitehouse BG, Yeats PA, Strain PM (1990) Cross-flow filtration of colloids from aquatic environments. Limnol Oceanogr 35 1368-1375... 

LA Mer, V. K. Disc. Faraday Soc. 42 (1966) 248. Filtration of colloidal dispersions flocculated by anionic and cationic polyelectrolytes. 

Wang, L.K. Role of polyelectrolytes in the filtration of colloidal particles from water and wastewater. Separ. Purif. Meth. 1977, 6 (7), 153-187. 

Electrostatic. Virtually all colloids in solution acquire a surface charge and hence an electrical double layer. When particles interact in a concentrated region their double layers overlap resulting in a repulsive force which opposes further approach. Any theory of filtration of colloids needs to take into account the multi-particle nature of such interactions. This is best achieved by using a Wigner-Seitz cell approach combined with a numerical solution of the non-linear Poisson-Boltzmann equation, which allows calculation of a configurational force that implicitly includes the multi-body effects of a concentrated dispersion or filter cake. 

W.R. Bowen and F. Jenner, Theoretical descriptions of membrane filtration of colloids and fine particles an assessment and review, Adv. Colloid Interface Sci. 56 (1995) 141-200. 

Precipitates obtained from dilute or very concentrated solutions are often in the form of very fine crystals. These fine precipitates will generally become filterable if allowed to stand for some time in contact with the mother liquor, preferably, if the solubility permits, near the boiling point of the solution. The addition of macerated filter paper is beneficial in assisting the filtration of colloidal precipitates. The macerated filter paper increases the speed of filtration by retaining part of the precipitate and thus preventing the clogging of the pores of the filter paper. 

Chen V, Fane AG, Madaeini S, and Wenten IG. Particle deposition during membrane filtration of colloids transition between... 

Bacchin, P., Si-Hassen, D., Starov, V., Clifton, M.J., and Aimar, P., A unifying model for concentration polarization, gel-layer formation and particle deposition in cross-flow membrane filtration of colloidal suspensions, Chem. Eng. Sci., 57, 77, 2002. 

Chen, V., Fane, A.G., Madeini, S., and Wenten, I.G., Particle deposition during membrane filtration of colloids Transition between concentration polarization and cake formation, J. Membr. Sci., 125, 109, 1997. 

In groundwaters distant from the engineered portions of a high-level waste repository the mobilities of U and Th may be limited by adsorption at low U and Th concentrations and by the solubilities of U and Th solids at higher concentration. In the same groundwaters, the mobilities of Ra, I, Tc, Np, and Pu are more likely to be limited (if they are limited) by adsorption and/or by coprecipitation in the structures of major mineral precipitates, or by the instability or filtration of colloids. Explain these statements and discuss the possible detailed behavior of each element. 

The use of ultrafiltration (UF) membranes for the separation of dissolved molecules of different size and nature has seen an increased interest in recent years. Depending on their pore size, membranes can be used in a variety of fields, such as removal of particulates from air, filtration of colloidal suspensions, treatment of product streams in the food and beverage industry, recovery of useful material from coating or dyeing baths in the automobile and textile industries and treatment of industrial waste waters (J, 2 ). UF membranes also serve as supports for ultrathin reverse osmosis (composite) membranes. 

In the past ten to fifteen years or so, the applications sphere of cross-flow filtration has been extended to include microfiltration (MF) which primarily deals with the filtration of colloidal or particulate suspensions with size ranging from 0.02 to about 10 microns. Microfiltration applications are rapidly developing and range from sterile water production to clarification of beverages and fermentation products and concentration of cell mass, yeast, E-coli and other media in biotechnology related applications. 

Sintered membranes are made on a fairly large scale from ceramic materials, glass, graphite and metal powders such as stainless steel and tungsten.9 The particle size of the powder is the main parameter determining the pore sizes of the final membrane, which can be made in the form of discs, candles, or fine-bore tubes. Sintered membranes are used for the filtration of colloidal solutions and suspensions. This type of membrane is also marginally suitable for gas separation. It is widely used today for the separation of radioactive isotopes, especially uranium. 

In summary, although the MF of coUoids is generally well understood, the literature is somewhat limited in the areas of filtration of colloids much smaller than the membrane pore size, and in systems where aggregation occurs. Systems are, in this regard, often poorly characterised, especially in the presence of humic substances. As shown in Chapter 2 organics stabilise inorganic colloids at sizes much smaller than pores, and their behaviour in MF or surface waters is largely unknown. 

Filtration of colloids at pH extremes served as a baseline of colloids, which are neither aggregated nor stabilised by an adsorbed organic layer. As expected from the literature review, the particle size closest to the membrane pore size (250 nm) caused largest flux decline. Rejection occurred in this case due to a combination of hydrophobic, specific, and van der Waals forces, and could not be explained by charge interaction only. Blocking law analysis showed evidence of pore blocking, cake formation, adsorption and pore closure at some stage of the filtration process. 

McDonogh R.M., Fane A.G., Fell C.J.D. (1989), Charge effects in the cross-flow filtration of colloids and... 

Nazzal F.F., Wiesner M.R. (1993), The effect of pH and ionic strength on the cross-flow filtration of colloidal silica and humic solutions using ceramic membranes, Proc. of AWWA Membrane Technology Conf, Baltimore, Aug 93, 93-104. 

Another important problem that has attracted the attention of a host of investigators (Ruckenstein and Prieve, 1973 Saville, 1977 Spielman, 1977 Tien and Payatakes, 1979) is particle collection. In the deep bed filtration of colloidal particles, one seeks to describe the interaction and the collision between one colloidal particle and one grain of the packing material that forms the bed. The latter, called the collector, is immobile. The liquid containing the suspended colloidal particles flows past the collectors and flocculation of the colloid particles with the grains of the packing material is called particle capture. The particles are brought to the collector surface both by convection and diffusion. 

Schafer, B., M. Hecht, J. Harting, and H. Nirschl. 2010. Agglomeration and filtration of colloidal suspensions with DVLO interactions in simulation and experiment. Journal of Colloid and Interface Science 349, no. 1 186-195. doi 10.1016/j.jcis.2010.05.025. 

Whitehouse, B.G, G Petrick, and M. Ehihardt. 1986. Crossflow filtration of colloids from Baltic Sea water. Water Res. 20 1599-1601. 

Cabane, B., Meireles, M., and Aimar, P. (2002). Cake collapse in frontal filtration of colloidal aggregates Mechanisms and consequences. Desalination 146, 155-161. 

Chun, M.-S., H. I. Cho, and I. K. Song. 2002. Electrokinetic behavior of membrane zeta potential during the filtration of colloidal suspensions. Desalination 148 363-368. 

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