Particulate matter, colloidal

Ultrafiltration, like reverse osmosis, is a pressure-driven membrane separation process. The applied pressures usually range from about 7 X 10" to 7 X 10 Pa, and the solvent, most often water, passes through the membrane. Material that does not pass through the membrane includes particulate matter, colloids, suspensions, and dissolved macromolecules of molecular weight generally greater than 10,000 and often greater than 2000. Rejection is usually close to complete. 

Applications of Dielectrophoresis Over the past 20 years the use of DEP has grown rapidly to a point at which it is in use for biological, colloidal, and mineral materials studies and handfing. The effects of nonuniform elec tric fields are used for handling particulate matter far more often than is usually recognized. This includes the... 

Major problems inherent in general applications of RO systems have to do with (1) the presence of particulate and colloidal matter in feed water, (2) precipitation of soluble salts, and (3) physical and chemical makeup of the feed water. All RO membranes can become clogged, some more readily than others. This problem is most severe for spiral-wound and hollow-fiber modules, especially when submicron and colloidal particles enter the unit (larger particulate matter can be easily removed by standard filtration methods). A similar problem is the occurrence of concentration-polarization, previously discussed for ED processes. Concentration-polarization is caused by an accumulation of solute on or near the membrane surface and results in lower flux and reduced salt rejection. 

Soils are commonly named and classified according to the general size range of their particulate matter. Thus sandy, sih and clay types dwive their names from the predominant size range.of inorganic cons tiiuents. Particles between 0 07 and about 2 mm are classed as sands. SUt particles range from 0-005 mm to 0-07, and clay particle Size ranges from 0-005 mni mean diameter down to colloidal matter. 

Baskaran and Santschi (1993) examined " Th from six shallow Texas estuaries. They found dissolved residence times ranged from 0.08 to 4.9 days and the total residence time ranged from 0.9 and 7.8 days. They found the Th dissolved and total water column residence times were much shorter in the summer. This was attributed to the more energetic particle resuspension rates during the summer sampling. They also observed an inverse relation between distribution coefficients and particle concentrations, implying that kinetic factors control Th distribution. Baskaran et al. (1993) and Baskaran and Santschi (2002) showed that the residence time of colloidal and particulate " Th residence time in the coastal waters are considerably lower (1.4 days) than those in the surface waters in the shelf and open ocean (9.1 days) of the Western Arctic Ocean (Baskaran et al. 2003). Based on the mass concentrations of colloidal and particulate matter, it was concluded that only a small portion of the colloidal " Th actively participates in Arctic Th cycling (Baskaran et al. 2003). 

When an ophthalmic ointment is manufactured, all raw material components must be rendered sterile before compounding unless the ointment contains an aqueous fraction that can be sterilized by heat, filtration, or ionizing radiation. The ointment base is sterilized by heat and appropriately filtered while molten to remove extraneous foreign particulate matter. It is then placed into a sterile steam-jacketed kettle to maintain the ointment in a molten state under aseptic conditions, and the previously sterilized active ingredients) and excipients are added aseptically. While still molten, the entire ointment may be passed through a previously sterilized colloid mill for adequate dispersion of the insoluble components. 

A significant fraction of lead carried by river water is expected to be in an undissolved form, which can consist of colloidal particles or larger undissolved particles of lead carbonate, lead oxide, lead hydroxide, or other lead compounds incorporated in other components of surface particulate matters from runoff. Lead may occur either as sorbed ions or surface coatings on sediment mineral particles, or it may be carried as a part of suspended living or nonliving organic matter in water. The ratio of lead in suspended solids to lead in dissolved form has been found to vary from 4 1 in rural streams to 27 1 in urban streams (Getzetal. 1977). 

Waste water from a drain or rain-overflow usually contains sediment, including sand, dust and solid particles such as grit. But smaller, colloidal particles also pollute the water. Water purification requires the removal of such particulate matter, generally before disinfecting the water and subsequent removal of any water-soluble effluent. 

Coagulants are used to bind together particulate and colloidal matter so they may be filtered from the feed before the membrane process. Coagulants can be either inorganic (such as ferric salts) or organic polyelectrolytes. The correct dosage and... 

Finally, completely equating the "mobile phase with solvent (e.g. pyridine) extractable "bitumen in coal ignores the potential presence of colloidal particulate matter in the pyridine extracts as well as possible solvent-induced scission of weak chemical bonds. Furthermore, the solvent-extractable fraction may well include macromolecular components, such as resinites. 

The link between colloids and surfaces follows naturally from the fact that particulate matter has a high surface area to mass ratio. The surface area of a 1cm diameter sphere (4jtr ) is 3.14 cm, whereas the surface area of the same amount of material but in the form of 0.1 pm diameter spheres (i.e. the size of the particles in latex paint) is 314 000 cm. The enormous difference in surface area is one of the reasons why the properties of the surface become very important for colloidal solutions. One everyday example is that organic dye molecules or pollutants can be effectively removed from water by adsorption onto particulate activated charcoal because of its high surface area. This process is widely used for water purification and in the oral treatment of poison victims. 

Reactions of dissolved species with particulate and colloidal suspended matter include adsorption/desorption, complexation, ion-exchange, precipitation/dissolution, coprecipitation during coagulation and flocculation (Morgan, 1966 Stumm and Morgan, 1981 Parks, 1975). These processes are particularly important at the land-sea boundary in estuaries (Duinker, 1980 Martin et al., this volume). The interaction with particles > 0.45 ym is not discussed here. 

Sorption coefficients quantitatively describe the extent to which an organic chemical is distributed at equilibrium between an environmental solid (i.e., soil, sediment, suspended sediment, wastewater solids) and the aqueous phase it is in contact with. Sorption coefficients depend on (1) the variety of interactions occurring between the solute and the solid and aqueous phases and (2) the effects of environmental and/or experimental variables such as organic matter quantity and type, clay mineral content and type, clay to organic matter ratio, particle size distribution and surface area of the sorbent, pH, ionic strength, suspended particulates or colloidal material, temperature, dissolved organic matter (DOM) concentration, solute and solid concentrations, and phase separation technique. 

Silt is formed by suspended particulates of all types that accumulate on the membrane surface. Typical sources of silt are organic colloids, iron corrosion products, precipitated iron hydroxide, algae, and fine particulate matter. A good predictor of the likelihood of a particular feed water to produce fouling by silt is the silt density index (SDI) of the feed water. The SDI, an empirical measurement (ASTM Standard D-4189-82,1987), is the time required to filter a fixed volume of... 

Sedimentation FFF implies application of the centrifugal field, which is produced by placing the channel in a centrifuge basket. SdFFF instruments can be linked readily to analytical instruments to provide analysis in real time. For the first time, Beckett (1991) introduced FFF-ICP-mass spectroscopy (MS) as a powerful analytical tool for characterizing macromolecules and particles. Taylor et al. (1992) illustrated the characterization of some inorganic colloidal particles and river-borne suspended particulate matter of size range <1 pm using SdFFF and ICP-MS. 

Other analytical tools have also been used as offline detectors for the FFF techniques. Bio et al. (1995) used for this purpose a graphite furnace atomic absorption spectrometer (GFAAS) to analyze colloidal kaolin particles. Contado et al. (1997) used same design to characterize river-suspended particulate matter of size <1 pm. However, the centrifuges available for SdFFF are only capable of separating particles with sizes down to 80 nm. Usage of SdFFF for characterization of HS is therefore restricted because of this limitation. 

Benedetti, M., Ranville, J.F., Ponthieu, M. and Pinheiro, J.P. (2002) Field-flow fractionation characterization and binding properties of particulate and colloidal organic matter from the Rio Amazon and Rio Negro, Organic Chemisrty 33, 269-279. 

Sub-division of particulate matter (e.g. separation of denser particles from colloids) can be achieved by centrifuging but the efficiency of the process depends on the size and density of the particles, and the speed and duration of the centrifugation. 

Study of the behaviour and properties of colloidal and particulate matter - Improvement of the measurement techniques currently available, particularly in the submicrometre range, as well as development of the theory necessary to describe the interactions between small colloids and organic matrices is needed. New techniques such as AFM or fluorescence correlation spectroscopy may give information on the conformation characteristics of such molecules as well as their adsorption and aggregation properties. 

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