Particle destabilization

There are four principal mechanisms by which particle dispersions can be destabilized (Benjamin and Lawler, 2013)  

Neutralization of the surface charge hy adsorption of counter-ions 

Addition of electrol3des to compress the thickness of the diffuse layer 

Addition of surface active organics that provide interparticle bridging 

Formation of a precipitate that captures particles in a sweep floe 

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The importance of the thin film between the mineral particle and the air bubble has been discussed in a review by Pugh and Manev [74]. In this paper, modem studies of thin films via SFA and interferometry are discussed. These film effects come into play in the stability of foams and froths. Johansson and Pugh have studied the stability of a froth with particles. Small (30-/ m), moderately hydrophobic 6c = 65°) quartz particles stabilized a froth, while more hydrophobic particles destabilized it and larger particles had less influence [75]. 

It has been observed for more than 30 years that preozonation ahead of particle removal units can improve the efficiency significantly, can induce a lower coagulant demand or allow higher flow rates, e. g. in deep-bed filtration. Ozone gas is added either before or together with the coagulant (ferric or aluminum salts or cationic polymers) at rather low dosages of 0.5-2 mg L l. The terms microflocculation or ozone-induced particle destabilization are used in practice (Jekel, 1998). 

TJhe aggregation of particles in a colloidal dispersion proceeds in two distinct reaction steps. Particle transport leads to collisions between suspended colloids, and particle destabilization causes permanent contact between particles upon collision. Consequently, the rate of agglomeration is the product of the collision frequency as determined by conditions of the transport and the collision efficiency factor, the fraction of collisions leading to permanent contact, which is determined by conditions of the destabilization step (2). Particle transport occurs either by Brownian motion (perikinetic) or because of velocity gradients in the suspending medium (orthokinetic). Transport is characterized by physical parame-... 

The rate of coagulation depends upon the collision frequency, which is controlled by physical parameters describing perikinetic or ortho-kinetic particle transport (temperature, velocity gradient, number concentration and dimension of colloidal particles), and the collision efficiency factor a measuring the extent of the particle destabilization which is primarily controlled by chemical parameters. 

Paode RD, Chandrankanth MS, Amy GL, Gramith JT, Ferguson DW. Ozone versus ozone/peroxide induced particle destabilization and aggregation a pilot plant. Ozone Sci Eng 1995 17 25-51. 

Hematite particles destabilized with salt, dp estimate assumes that aggregate size (R) is proportional to time as Roctl/d dp estimated by curve-fitting. 

Figure 33. Pseudoemulsion film formed between mixed antifoam (oil with hydrophobic particles) and air, on the tip of a glass capillary (schematic). The film area is increased by pushing the antifoam out of the capillary. The particles destabilize the pseudoemulsion film by partially submerging into the aqueous phase.

PSEUDOEMULSION FILM PSEUDOEMULSION FUJI PARTICLES DESTABILIZE... 

An additional potential application of particulate counting is process control and monitoring. With the improvement in aqueous particle counters, on-line measurement of number concentrations and size distributions for particulates larger than 1-2 pm is now feasible. Both feedforward and feedback process control applications can be envisioned. Feed-forward control could be used to estimate the coagulant chemical requirements needed for particle destabilization based on measurement of particle count and estimation of particulate surface area (32). Feedback control possibilities include control of the particle size distribution entering a filter, control of chemical dosing prior to granular-media filtration, and control of filter operation. 

Doll, B., Particle destabilization in turbulent pipe flow , Proc. 14th lAWPRC Biennial International Conference (Brighton, 1988), Book 2, pp. 435-442, lAWPRC, London (1988)... 

That the liquid hydrophobic oils formed above their respective melting temperatures are ineffective is a consequence of the metastability of the relevant pseudoemulsion films, as we have discussed elsewhere (see, e.g.. Section 3.3). In the case of the impure materials where a region of mixed solid and liquid phase exists, it seems likely that the solid component is able to destabilize those films. Similar effects have been described in oil-in-water emulsion systems where partial melting leads to instability of the oil-water-oil films due the presence of crystals at the oil-water surface [204-206]. We address the effect of particle destabilization of pseudoemulsion films on antifoam action in the following section. 

Chheda, P. and Grasso, D. (1994) Siurface thermodynamics of ozone-induced particle destabilization Langmuir, 10, 1044-1053. 

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