Flocculation properties, various

Adsorption of nonionic and anionic polyacrylamides on kaolinite clay is studied together with various flocculation properties (settling rate, sediment volume, supernatant clarity and suspension viscosity) under controlled conditions of pH, ionic strength and agitation. Adsorption and flocculation data obtained simultaneously for selected systems were correlated to obtain information on the dependence of flocculation on the surface coverage. Interestingly, optimum polymer concentration and type vary depending upon the flocculation response that is monitored. This is discussed in terms of the different properties of the floes and the floe network that control different flocculation responses. Flocculation itself is examined as the cumulative result of many subprocesses that can depend differently on system properties. 

In order to generate information on the mechanism of flocculation by polymers it is, however, necessary to correlate flocculation with various system properties, particularly adsorption. Thus, if particle/polymer-polymer/particle contact is the aggregation mechanism, the flocculation responses should be expected to continuously increase with surface coverage. On the other hand, if particle/polymer-particle contact is predominant and if the polymer adsorption is essentially irreversible, maximum flocculation might be expected under submonolayer conditions. In order to determine the nature of this relationship for the present systems, selected flocculation responses are plotted in Figures 8 and 9 as a function of surface coverage for the nonionic and the anionic polymer respectively. The assumptions involved in the computation of the surface coverage are to be noted at this point ... 

Vinyl copolymers substituted with -OH, -0-R, -0C(0)-R, -C(0)-R, or -C5H4N groups have various practical applications, depending on their composition. These applications include uses in glues, lacquers, protective films, flocculent agents, various formulations in cosmetics (e.g. poly(1-vinyl-2-pyrrolidinone-co-ethyl methacrylate-co-methacrylic acid) is used in hair spray formulations, poly(1-ethenyl-2-pyrrolidinone-co-1-eicosene) is used as a pigment dispersant in cosmetics), etc. A number of pyrolysis studies were done on these materials [43], etc. Some thermal properties of a few common vinyl copolymers are summarized in Table 6.5.14. 

Yokoi, H Obita, T Hirose, J Hayashi, S Takasaki, Y. Flocculation properties of pectin in various suspensions. Bioresource Technology, v.84, p.287-290,2002. 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

Lignin amines with high nitrogen content are water soluble at both alkaline and acidic pH values. The lignin amines have various useful properties. For example, they are active as flocculants, filtration aids, scale inhibitors, fluid loss additives, oil well cement additives, and corrosion inhibitors among other potential uses. The nitrogen is introduced into the lignins with the Mannich reaction [1570]. 

The results of this study clearly show the complex dependence of the flocculation process on polymer dosage and charge density. It is seen that the form of dependence varies markedly among the responses monitored. In addition to the factors studied here, it can also be expected to depend upon several other physicochemical conditions of the system, including the type of mixing. The final state of flocculation achieved by a mineral/polymer system will depend upon many interactions in the system as determined by various chemical and hydrodynamic properties of the particles, polymer, dissolved organics and the fluids. 

Among the properties measured here, the settling rate is mainly a measure of the size of the floes and in later stages the compressibility of floes and floe networks, and the supernatant clarity is a measure of the size distribution of floes and size dependent capture of the particles and floes by the polymer. The sediment volume and the pulp viscosity on the other hand, are direct measures, not only of floe size and structure but also of adsorbed polymer layers. It is to be noted in this regard that it is this latter aspect which makes it possible to estimate the thickness of adsorbed polymer layers by measuring the viscosity of the medium and the suspension in the presence of polymers (20,21). This combination of effects is another reason one cannot always expect correlation between various flocculation responses. 

An emulsion is a dispersed system of two immiscible phases. Emulsions are present in several food systems. In general, the disperse phase in an emulsion is normally in globules 0.1-10 microns in diameter. Emulsions are commonly classed as either oil in water (O/W) or water in oil (W/O). In sugar confectionery, O/W emulsions are most usually encountered, or perhaps more accurately, oil in sugar syrup. One of the most important properties of an emulsion is its stability, normally referred to as its emulsion stability. Emulsions normally break by one of three processes creaming (or sedimentation), flocculation or droplet coalescence. Creaming and sedimentation originate in density differences between the two phases. Emulsions often break by a mixture of the processes. The time it takes for an emulsion to break can vary from seconds to years. Emulsions are not normally inherently stable since they are not a thermodynamic state of matter. A stable emulsion normally needs some material to make the emulsion stable. Food law complicates this issue since various substances are listed as emulsifiers and stabilisers. Unfortunately, some natural substances that are extremely effective as emulsifiers in practice are not emulsifiers in law. An examination of those materials that do stabilise emulsions allows them to be classified as follows ... 

The surface character of fibres influences their affinity towards various chemical additives by, for example, their adsorption properties and also in their tendency to flocculate. Cellulosic fibres, because of the presence of acidic groups which are introduced during chemical pulping and bleaching, are mildly anionic. These acidic groups may be carboxylic (COOH) or in some cases sulfonic acid (S03H) and they are able to dissociate to leave a net negative... 

While for the complexation with poly(sodium styrene sulfonate) or sodium cellulosesulfate 1 1 stoichiometry has been reported [150] a non-stoichiometric complex results with sodium carboxymethylcellulose [150]. Optimized conditions make it possible to create membranes with various properties using the PDADMAC/sodium cellulosesulfate system [166-168]. However, the symplex formation with PDADMAC or copolymers mostly results in flocculated precipitates [27,150,169]. Highly ordered mulilayer assemblies were prepared by alternate reaction of PDADMAC and various polyanions [170,171]. Recently, the efficiency and selectictivity of protein separation via PEL coacervation were examined using PDADMAC [172]. 

In 1954, Jeanes et al.5 reported the formation of glucan(s) by 96 strains of bacteria that were primarily Leuconostoc strains. (There is a question here as to whether they are strains or species, particularly with regard to the formation of different kinds of polysaccharides. The classification of the time was to place them into one species, mesenteroides, that had several different strains. This classification stands today.) The polysaccharides were characterized by various properties such as optical rotation, viscosity, periodate oxidation profile, and physical appearance after alcohol precipitation. The latter were observed to have different appearances, which were described by Jeanes et al.5 in various qualitative terms such as pasty, fluid, stringy, tough, long, short, flocculent, and so on. These differences in appearance provided an early suggestion of differences in structure (see Table I). Both water-soluble and water-insoluble polysaccharides were formed, and some strains seemed to form more than one kind of polysaccharide, as judged by their water solubility and by differences in the amount of alcohol needed to precipitate them. 

The various industrial uses of starch depend in large measure on the properties of the individual fractions. A starch paste may function in two ways it may be used for its flocculating, its adsorptive, or its gel qualities or it may act as a sol or protective colloid. These properties derive directly from the A and B fractions, respectively. In many instances, it appears that only one action is required, and that the presence of the other starch component may even be detrimental. Thus, Hixon and Sprague have reported superior qualities for waxy maize starch in those applications for which stability and protective colloid action are requisite. 

Traditionally, M. oleifera seeds have been used to clarify turbid waters in rural areas of Asia and Africa (29). Of the identified 14 species of the moringaceae family, M. oleifera has gained considerable importance as flocculants in nearly all tropical and subtropical regions (8). Further, the coagulating property of the seed powder of this plant has been used for various aspects of water treatment such as turbidity, alkahnity, total dissolved sohds, and hardness (30, 51,54, 63). The seeds of six more frequent and cultivated species of Moringa have been found to contain flocculant components. Numerous studies so far confirms that M. oleifera seeds possess effective coagulation properties (49,54,63,65). Branches of the M. oleifera when lopped and thrown into turbid and contaminated wells, over an episode of time, the previously dirty water becomes clear. The desiccated M. oleifera seeds are... 

Although this picture is remarkably generic, the mechanisms responsible for the formation of a particle-lean layer adjacent to the wall depend on the properties of the material under consideration. For the case of solid particle dispersions, wall depletion, particle migration, and solid-liquid separation are the most frequent sources of solvent layer lubrication. Wall depletion occurs whenever dispersions are brought into contact with smooth and solid surfaces because the suspended particles cannot penetrate rigid boundaries [147]. Particle migration is due to various forces arising from fluid inertia, fluid elasticity, and shear-induced diffusivity effects [165]. Solid-liquid separation, which frequently occurs in flocculated suspensions like... 

In a recent study, the necessity for understanding the effects that molecular probes (e.g., pyrene) can have on colloidal system has been clearly illustrated. " Mixtures of pyrene-labeled and unlabeled polyethylene oxide (PEO) were adsorbed on silica and the properties of the resulting suspension were monitored. Settling rate results (Eigure 7.29) clearly demonstrated that pyrene-labeled PEO has a marked effect on the flocculation of silica suspension. It has been shown that even relatively small amounts of labeled polymer, when mixed with unlabeled polymer, can dramatically affect the behavior of their mixtures. On the other hand, it has also been shown that when labeled polymer was used in sufficiently low amounts (<3%), the mixture behavior does not differ from that due to the unlabeled polymer. These findings once again underscore the fact that while certain measurement techniques are invaluable for investigating colloidal phenomena, potential effects caused by introduction of various molecular probes into the system should always be noted. 

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