Flocculating concentration

The most commonly used inorganic polymers are the polyacrylamides. Chemical flocculant concentrations employed normally range from 100 to 500 mg/Liter. The wastewater pH may require adjustment between 4.5 and 5.5 for the ferric compounds or between 5.5 and 6.5 for the aluminum compounds using an acid such as H2SO4 or a base such as NaOH. In many applications, the DAF effluent requires additional pH adjustment, normally with NaOH to assure that the effluent pH is within the limits specified by the POTW.. The pH range of the effluent from a DAF is typically between 6 and 9. 

Table VI Critical Coagulation/Flocculation Concentration and the slope of log W vs log C plot...

Figure 7 Relationship between critical flocculation concentration(CFC) and concentration of HPC-M for HPC-latex systems.

The crucial question is at what value of <)> is the attraction high enough to induce phase separation De Hek and Vrij (6) assume that the critical flocculation concentration is equivalent to the phase separation condition defined by the spinodal point. From the pair potential between two hard spheres in a polymer solution they calculate the second virial coefficient B2 for the particles, and derive from the spinodal condition that if B2 = 1/2 (where is the volume fraction of particles in the dispersion) phase separation occurs. For a system in thermodynamic equilibrium, two phases coexist if the chemical potential of the hard spheres is the same in the dispersion and in the floe phase (i.e., the binodal condition). 

To (obtained from extrapolation of the ascending part of the flow curve) as a function of C. The shear modulus, GQ, measured using the pulse shearometer, is also shown as a function of C in the same figure. A measurable x and GQ is obtained above a critical value of C, which in both cases is -0.22 mol dm 3. As we will see later, this electrolyte concentration should be taken as the critical flocculation concentration (CFC) for the concentrated dispersion. Above the CFC, xg increases rapidly with increasing C whereas G initially increases gradually with increasing C until C = 0.3 mol dm 3, above which there is a more rapid increase of Gq. 

It is seen that the flocculation rates are generally considerably lower than the coagulation rate. A "pseudo" optimum flocculation concentration of 6 OFC units is found for short flocculation times, but for longer times it is clear that the suspension is stabilized and no further flocculation occurs. At higher initial doses restabilization becomes even more pronounced. ... 

The method described here provides a convenient means of determining the specific filtration resistance of fairly dilute suspensions. Results for clay suspensions flocculated by cationic polymers show that the specific resistance gives a sensitive indication of flocculation and is a useful guide in the selection of optimum flocculant concentrations. In a series of trials not reported here, it has been shown that the specific resistance results are very well matched by re-filtration rate data, as expected. The results also agree well with other, unrelated techniques. For more concentrated suspensions, some discrepancies have been found between permeability methods and other measures of flocculation (4). 

Even though the new technique is largely automated, it is still a rather lengthy procedure, compared to some other methods of flocculation testing (13), and would probably not be used simply to find optimum flocculant concentrations. 

Critical currents, 23 821-823 in superconducting, 23 819-825 Critical event (CE), 15 462 Critical failure, 26 982 Critical features, in separating nonideal liquid mixtures, 22 307 Critical fields, thermodynamic, 23 809-811 Critical flocculation concentration, 11 631 Critical item evaluation, for reliability, 26 991... 

Polymers may show an optimum flocculation concentration which depends on molecular weight and concentration of solids in suspension. Overdosing with flocculant may lead to restabilisation(44), as a consequence of particle surfaces becoming saturated with polymer. Optimum flocculant concentrations may be determined by a range of techniques including sedimentation rate, sedimentation volume, filtration rate and clarity of supernatant liquid. 

Keywords Additional discharge streams Antisealants Chemical treatment Coagulation/flocculation Concentration factor Dechlorination Filtration High recovery Membrane cleaning Pretreatment Recovery rate... 

Panayiotopoulos KP, Barbayiannis N, Papatolios K (2004) Influence of electrolyte concentration, sodium adsorption ratio, and mechanical disturbance on dispersed clay particle size and critical flocculation concentration in alfisols. Comm Soil Sci Plant Anal 35 1415-1434... 

The flocculation concentrations of mono-, di-, and trivalent gegen ions should, from this theory, be expected as... 

Several major barriers need to be overcome for the development of nonviral gene delivery systems into true therapeutic products for use in humans. These barriers fall into three classes manufacturing, formulation, and stability (extracellular barriers and intracellular barriers) (85). Cationic lipids and cationic polymers self-assemble with DNA to form small particles that are suitable for cellular uptake. At the therapeutic doses positively charged particles readily aggregate as their concentration increases, and are quickly precipitated above their critical flocculation concentration. 

Larpent and Tandros [102] prepared microlatex particles by polymerization of PEO-MA macromonomer with MMA, styrene, and vinyl acetate. The nonionic latexes are very stable, giving no flocculation up to 6 mol dm 3 NaCl or CaCl2 and a critical flocculation concentration (CFC) of 0.6 mol dm 3 for Na2S04 or MgS04 was estimated. Charged latexes are less stable than the nonionic ones. The CFC of all latexes are determined as a function of electrolyte concentration. With the nonionic latexes, however, the critical flocculation temperature (CFT)... 

The lower rejection ratio of 16 was accompanied by high selectivity in pyritic sulfur dispersion. This was due to the higher (10 mg/l) flocculant concentration which resulted in higher coal yield (93.1 wt) in the flocculated fraction. On the other extreme, when higher dispersant concentration (500 mg/l) was used with lower flocculant concentration (2 mg/l), much less coal was flocculated (77 wt) and more sulfur was apparently rejected (39 ). The intermediate conditions of 300 mg/l PAAX dispersant and 2 mg/l flocculant produced correspondingly intermediate results. 

Aggregates like polyelectrolyte complexes having positive charges and hydrophobic domains show a broader optimum flocculation concentration range and are considered as new reactive nanoparticles [11-14], Thus, polycations with hydrophobic functionalities represent an interesting class of water-soluble associating polyelectrolytes relevant for controlled stabilization/flocculation of dispersions in numerous industrial applications. 

This is expected since the extrapolation procedure usually overestimates the yield value. The data of Figs. 3 and 4 show a rapid increase in yield value above a critical PEO concentration, 4. This concentration corresponds to the critical flocculation concentration of the free polymer. However, since the rise in Tg did not occur at a sharp value, the latter was taken as the intersection point at which the extrapolated hprizontal and vertical lines meet. This gave values of 4 of 0.02 0.002, O.OItO.001 and O.OOStO.OOl for PEO with of 20,000, 35,000 and 90,000 respectively. Moreover, the 4p values obtained from the two sets of rheological results were almost the scime within the error of locating p. 

Oxide particles Above the stoichiometric line, excess polymer coexists with fully covered spheres. Below the stoichiometric line, excess spheres cause unlimited bridging and the separation of a concentrated gel from the pure solvent. Then at even lower polymer concentrations, below the optimum flocculation concentration (o.f.c.), the gel can no longer accommodate all the spheres, and some are rejected. 

When the electrostatic stabilization of the emulsion is considered, the electrolytes (monovalent and divalent) added to the mixture are the major destabilizing species. The zeta potential of the emulsion particles is a function of the concentration and type of electrolytes present. Two types of emulsion particle-electrolyte (ions) interaction are proposed non-specific and specific adsorption.f H non-specific adsorption the ions are bound to the emulsion particle only by electrical double-layer interactions with the charged surface. As the electrolyte concentration is increased, the zeta potential asymptotes to zero. As the electrostatic repulsion decreases, a point can be found where the attractive van der Waals force is equal to the repulsive electrostatic force and flocculation of the emulsion occurs (Fig. 9A). This point is called the critical flocculation concentration (CFC). 

Some product is sold in slurry which is a convenient form since it eliminates dust, saves energy, and lowers the cost. The industries which are frequent users of such product are paper and paints. Many other applications require material to be in a powder form, therefore the sluny is flocculated, concentrated (filter presses), and dried. Several dryer types are used such as rotary, tray, fluidized bed process or spray. The clay may be pulverized after some of these drying process depending requirements. Figure 2.34 shows the morphology of kaolin. A typical platy structure is clearly displayed on this photograph. 

Plots of log W versus log C are shown in Figure 10.28. The condition log W = 0 [W = 1) is the onset of fast flocculation. The electrolyte concentration at this point defines the critical flocculation concentration (CFG). Above the CFG, W<1 (due to the contribution of van der Waals attractions which accelerate the rate above the Smoluchowski value). Below the GFG, W > 1 and it increases with a decrease... 

The effect of the concentration of the potential-determining ions and the counterions on the interface potential of the particles has been discussed earlier in this section. Also, it was stated that the critical flocculation concentrations (CFG) of inorganic electrolytes of different valencies are related to each other in the following manner ... 

An interesting new result is the strong dependence of the radius on the ionic strength if this is increased before the addition of TES (A6, A7, and A8, Tables I and II). LiN03 was chosen to change the ionic strength because it dissociates completely in this concentration range (53). The flocculation concentration of the sol A6 was 5 mM of LiNC>3. 

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