Flocculation curve

With certain horse antitoxins and antiprotein sera and in some patients with Hashimoto s thyroiditis who have antibodies to thyro-globulin, one finds a different type of quantitative precipitation curve, termed a flocculation curve.Precipitation occurs only over a narrow range, and soluble antigen-antibody complexes are formed in the region of antibody excess as well as of antigen excess. Flocculation curves have... 

Figure 9 Domains of coagulation and flocculation. Curves 1 and 2 are calculated with the Rabinovich-Churaev Hamaker function a twice higher value is used for calculation of curves 1 and 2. The domain of flocculation is located above curve 1, while the domain of coagulation is located beneath curve 2. Volume fraction 0 = 0.01 (a) (j> = 0.l (b). Particle dimension 2a = 4 (xm. (From Ref 26.)...

Fig. 51. Illustrating the large difference in concentration of electrolyte for flocculation (curve f) and repeptization (curve ).

Fig. 3 Monoflocculation (curves 1 and 2) compared with dual flocculation (curves 3 and 4) of clay (10 g/L) in solutions of humic acid (HA) in water (25 or 50 mg/L) showing dependence of the absorption of the supernatant on the total amount of polymer used, PDADMAC was used for monoflocculation PDADMAC + HMW PA were used as dual system. Figure adapted from [26]...

Microwave-assisted Ag-g-PAM grades show better flocculation efficacy than conventional and microwave-initiated technique. Flocculation curves of comparative grades (Ag- -PAM 2 (C), Ag-g-PAM 2 (M.I), and Ag-g-PAM (M.A)) in wastewater with respect to agar and alum (coagulant) are graphically represented as in Figure 3.11. 

Fig. 4 Flocculation curve dependence on the degree of flocculation F on flocculant dosing...

The measurement and evaluation of flocculation state is typically carried out over 10 min by means of programmed dosing, in which the flocculation value F is recorded during a stepwise increase in flocculant dosing. Figure 4 shows an example of a flocculation curve. The amount of flocculant required for optimal flocculation is that where F reaches an asymptotic limit (bridging mechanism) or a maximum (patch charge mechanism). 

The flocculation curve of flocculant A is almost ideal after a short initiation or response time, during which the amount of polymer is still too low for sufficient destabilization of the particles, there is a significant increase in the degree of flocculation at higher polymer concentrations. The flocculation curve is linear over a wide range and finally approaches an asymptote at even higher polymer concentrations. The flocculation curves... 

Fig. 7 Flocculation curves for excess sludge with Sedipur products (Al, A2, A3) variation of molecular weight of Ae flocculants...

Fig. 8 Flocculation curves for excess sludge with Sedipur products variation of charge density A4 2.0 meq/g, A5 4.2 meq/g, A6 8.4 meq/g...

The time of day, the actual flocculation aid concentration, the change in the flocculation value in comparison with the previous concentration step (dF), and the absolute flocculation value (F) are given the bar chart corresponds to the flocculation curve shown before. The optimal flocculant concentration is defined as that at which increasing of the Sedipur concentration twice no longer increases the flocculation value by more than 20%. On the basis of this Sedipur concentration, which is transmit-... 

Often the van der Waals attraction is balanced by electric double-layer repulsion. An important example occurs in the flocculation of aqueous colloids. A suspension of charged particles experiences both the double-layer repulsion and dispersion attraction, and the balance between these determines the ease and hence the rate with which particles aggregate. Verwey and Overbeek [44, 45] considered the case of two colloidal spheres and calculated the net potential energy versus distance curves of the type illustrated in Fig. VI-5 for the case of 0 = 25.6 mV (i.e., 0 = k.T/e at 25°C). At low ionic strength, as measured by K (see Section V-2), the double-layer repulsion is overwhelming except at very small separations, but as k is increased, a net attraction at all distances... 

Studies of flow-induced coalescence are possible with the methods described here. Effects of flow conditions and emulsion properties, such as shear rate, initial droplet size, viscosity and type of surfactant can be investigated in detail. Recently developed, fast (3-10 s) [82, 83] PFG NMR methods of measuring droplet size distributions have provided nearly real-time droplet distribution curves during evolving flows such as emulsification [83], Studies of other destabilization mechanisms in emulsions such as creaming and flocculation can also be performed. 

Plastic fluids are Newtonian or pseudoplastic liquids that exhibit a yield value (Fig. 3a and b, curves C). At rest they behave like a solid due to their interparticle association. The external force has to overcome these attractive forces between the particles and disrupt the structure. Beyond this point, the material changes its behavior from that of a solid to that of a liquid. The viscosity can then either be a constant (ideal Bingham liquid) or a function of the shear rate. In the latter case, the viscosity can initially decrease and then become a constant (real Bingham liquid) or continuously decrease, as in the case of a pseudoplastic liquid (Casson liquid). Plastic flow is often observed in flocculated suspensions. 

A Delgado, V Gallardo, A Parrera, F Gonzalez-Ca-ballero. A study of the electrokinetic and stability properties of nitrofurantoin suspensions. II Flocculation and redispersion properties as compared with theoretical interaction energy curves. J Pharm Sci 79 709-718, 1990. 

The typical viscous behavior for many non-Newtonian fluids (e.g., polymeric fluids, flocculated suspensions, colloids, foams, gels) is illustrated by the curves labeled structural in Figs. 3-5 and 3-6. These fluids exhibit Newtonian behavior at very low and very high shear rates, with shear thinning or pseudoplastic behavior at intermediate shear rates. In some materials this can be attributed to a reversible structure or network that forms in the rest or equilibrium state. When the material is sheared, the structure breaks down, resulting in a shear-dependent (shear thinning) behavior. Some real examples of this type of behavior are shown in Fig. 3-7. These show that structural viscosity behavior is exhibited by fluids as diverse as polymer solutions, blood, latex emulsions, and mud (sediment). Equations (i.e., models) that represent this type of behavior are described below. 

The principle of this method is that the initial slope (time = zero) of the optical density-time curve is proportional to the rate of flocculation. This initial slope increases with increasing electrolyte concentration until it reaches a limiting value. The stability ratio W is defined as reciprocal ratio of the limiting initial slope to the initial slope measured at lower electrolyte concentration. A log W-log electrolyte concentration plot shows a sharp inflection at the critical coagulation concentration (W = 1), which is a measure of the stability to added electrolyte. Reerink and Overbeek (12) have shown that the value of W is determined mainly by the height of the primary repulsion maximum in the potential energy-distance curve. 

The major difference in the flocculation behaviour of PEG 40,000 at pH 5.3 and pH 2.3 is demonstrated by the absorbance in the supernatant solution E,., (fig. 13). At pH 2.3 a small addition of polymer leads to significant flocculation and therefore a small absorbance, i.e. a high transparency of the supernatant liquid. The time dependences of the absorbances with and without polymer are shown for pH 5.3 and ca.pH 2 in fig. 14. Fig. 15 shows similar curves for a selection of salt concentrations. Similarly the time dependence of the absorbances Ej with and without polymer is illustrated for pH 5.3 and ca.pH 2 in fig. 16 and for different salt concentrations in fig. 17. 

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. 

Gmin.in the free energy-particle separation curves. Since AS g is reduced in concentrated dispersions,the flocculation of the dispersion occurs at relatively lower Gm- n than that observed with dilute dispersions. Thus, this effect would result in a reduction of the CFC for concentrated dispersions. However, the net result of reduction of CFC may be due to a combination of this effect and depletion of electrolyte from the dense region of the adsorbed layers. 

Figure 1. Flocculation. Experimental and theoretical particle concentration vs. time. Initial dose in OFC units beside curves. Molecular weight 1x10, charge density 95%. Shear rate 1800 s-. ...

Figure 13.4 shows the titration curve of a palladium nitrate solution [Pd] = 5 g/L by soda [NaOH] = 0.1N. Three regions can be clearly distinguished, corresponding to a true solution (starting point until addition of about 14 mL of soda), to the formation of colloidal PdO particles (from 14 to 24 mL added), and to the flocculation of particles with segregation of liquid and solid phases (above 25 mL). 

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