Charge density flocculation

There are two main advantages of acrylamide—acryUc-based flocculants which have allowed them to dominate the market for polymeric flocculants in many appHcation areas. The first is that these polymers can be made on a commercial scale with molecular weights up to 10—15 million which is much higher than any natural product. The second is that their electrical charge in solution and the charge density can be varied over a wide range by copolymerizing acrylamide with a variety of functional monomers or by chemical modification. 

Flocculation is indeed dependent on polymer adsorption, and there are hypotheses correlating the two phenomena, but often these have been put forth without detailed measurement of the two phenomena simultaneously (10-13). In this paper, flocculation is investigated as a function of polymer and solution properties and hydrodynamic conditions by measuring different properties of the system, including adsorption, using well characterized kaolinite and polymer samples prepared specifically for this purpose. Also, the role of concentration and charge density of polyacrylamide and polyacrylamide-polyacrylic acid co-polymers in determining kaolinite flocculation is examined under controlled hydrodynamic conditions. 

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. 

Figure 7. Diagram illustrating the effect of polymer charge density on various flocculation responses of Na-kaolinite at pH 4.5.

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-. ...

When using more active emulsifiers of the C-10 type (Yeliseyeva, 1966) the effective rate and the equilibrium value of adsorption increase in the polymerization of polar monomers, which reduces the intensity of the processes of initial flocculation. Moreover, in this case the charge density is not the only stabilizing factor it is su(f>lemented by the enthalpy factor which arises from hydration of oxyethylenic chains of emulsifier molecules. The presence of these emulsifiers creates conditions that enable tbe obtain-ment of polar polymer latexes of high stability. 

Properties Off-white granular powder. Den 47-53 Ib/f3, pH of 0.5% solution at 77F 6.5-8.5. TM for a dry polyacrylamide cationic, flocculated with controlled molecular weight distribution and varying charge densities. 

Simple Charge Neutralization and Charge Patch Neutralization Oppositely charged polyelectrolytes reduce the particle surface charge density such that particles may approach each other sufficiently closely so that the attractive van der Waals force becomes effective. Flocculation caused by this mechanism should not be sensitive to the molecular weight of the polymer. 

Size and size distribution Shape Agglomeration, flocculation state Charge Density Liquid/solid ratio Viscosity Density pH Expression mechanism Pressure Temperature Operating time Filter medium Pretreatments... 

With new data for polyelectrolytes obtained with the techniques described above it should become possible to determine carefully the effects of ionic strength and externally controlled surface potential on the rate of adsorption of poly electrolytes. We hope that the effects of molar mass and charge density of the poly electrolyte, as well as the nature of that charge (annealed or quenched) can be established. This should stimulate further theoretical research aimed at constructing an adequate equivalent of the Von Smolu-chowsky-Fuchs theory for the rate of flocculation. At present, it would seem that an analysis of the adsorption process taking all complications into account necessitates a simulation-oriented approach. 

---