Polymer flocculation of calcite: Relating the aggregate size to the settling rate

Heath, Alex R.; Bahri, Parisa A.; Fawell, Phillip D.; Farrow, John

doi:10.1002/aic.10789

Cited by 65 publications

(44 citation statements)

References 42 publications

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“…Aggregation can be induced by different means one of the most common being based on the addition of polymeric additives, namely polyelectrolytes. Flocculation by polyelectrolytes is of importance to many industrial areas, namely in food manufacturing, pharmaceuticals and also in papermaking, and is well documented in the literature [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…Another traditional technique to monitor flocculation and to assess the performance of flocculants is based on settling tests in the absence of turbulence, monitored by different means [5,6], which can supply indirect information on flocs average size and structure [21] (namely the mass fractal dimension) for the conditions prevailing in a sedimentation system.…”

Section: Introductionmentioning

confidence: 99%

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The use of LDS as a tool to evaluate flocculation mechanisms

Rasteiro

Garcı́a

Ferreira

et al. 2008

Chemical Engineering and Processing: Process Intensification

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Flocculation studies of precipitated calcium carbonate induced by cationic polyacrylamides (C-PAMs) were carried out using light diffraction scattering (LDS). The effect of both polymer charge density and concentration on the flocculation process and on flocs density was investigated. As expected, results show that high charge density C-PAM induces flocculation by bridging and patching mechanisms simultaneously, while medium charge density C-PAM acts mainly according to the bridging mechanism. Consequently, the mass fractal dimensions of the flocs produced by high charge density C-PAM are higher. Results also show the effect of flocculant concentration: flocculation rate decreases and denser flocs are obtained as flocculant concentration increases. The results obtained so far allowed a preliminary quantitative evaluation of flocculation kinetics. In the flocculation curve, two regions corresponding to different kinetics were identified: a first region dominated by particle aggregation and a second region dominated by flocs stabilization. Therefore, LDS is considered a useful tool to evaluate flocculants performance. A strategy was developed that resulted in the use of LDS to retrieve, in a single test, information on the evolution with time of flocs dimension and structure, flocs resistance and flocculation kinetics. All the tests were performed under turbulent conditions similar to the ones prevailing in process equipment.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The use of LDS as a tool to evaluate flocculation mechanisms

Rasteiro

Garcı́a

Ferreira

et al. 2008

Chemical Engineering and Processing: Process Intensification

View full text Add to dashboard Cite

show abstract

“…Usually in dewatering applications one deliberately adds flocculants to the suspension, and these cause solid particles to aggregate together into flocs, with these flocs then settling faster than individual solid particles would (Heath et al, 2006). As the overall solids fraction becomes high enough however, the flocs can themselves network together into a weight bearing gel.…”

Section: Introductionmentioning

confidence: 97%

Designing thickeners by matching hindered settling and gelled suspension zones in the presence of aggregate densification

Zhang

Grassia

Martin

et al. 2015

Chemical Engineering Science

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A model is presented for design of a thickener for solid–liquid separation where the flocs or aggregates within the solid–liquid suspension undergo an aggregate densification process due to the action of rakes. This aggregate densification facilitates suspension dewatering. The novel feature of the model is that it manages to couple together a hindered settling zone (higher up in the thickener, where the flocs are separated from one another, and the suspension cannot bear weight) and a gelled suspension zone (lower down in the thickener, where the flocs are packed together, and the suspension is able to bear weight). The model determines solids fraction profiles throughout the hindered settling zone and the gelled suspension zone, and also gives zone heights and residence times. Parametric investigations using the model are carried out for different suspension fluxes (which influence the solids fluxes and underflow solids fractions attained), and also for different specified amounts of and rates of aggregate densification

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“…In these equations, A is a pre-exponential factor (μm), t is time (min) and k 1 and k 2 are the kinetic constants. The kinetic equations are written in terms of d 4,3 because, by doing so, it is easier to relate the growth of the aggregates with the decrease of the number of particles in the system, as is often done when describing flocculation kinetics [7]. Table 2 the values of the kinetic constants for the two stages, k 1 and k 2 , respectively, for the four PELs studied, are summarized.…”

Section: Flocculation Kineticsmentioning

confidence: 99%

“…Polyelectrolytes (PEL) are widely used to achieve efficient solid-liquid separation in many industries [1][2][3][4]. In the case of papermaking, flocculation is the most important phenomena of the…”

Section: Introductionmentioning

confidence: 99%

Using Light Scattering to Screen Polyelectrolytes (PEL) Performance in Flocculation

et al. 2011

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Flocculation of precipitated calcium carbonate (PCC) was monitored using light diffraction spectroscopy (LDS). Four cationic polyacrylamides of high molar mass and with different degrees of branching, all copolymers of acrylamide (AM) and acryloyloxyethyltrimethyl ammonium chloride (Q9), were tested. LDS supplied information about the kinetic curves for flocs growth and also for the flocs structure evolution. Flocculation kinetics, flocs size and structure, flocs resistance and reflocculation capacity could be correlated with the degree of branching of the polyelectrolytes (PEL). Furthermore, PEL with different degrees of branching corresponded to different values for the intrinsic viscosity, indicating differences in the polymer conformation, which explained well the performance differences in flocculation.

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Polymer flocculation of calcite: Relating the aggregate size to the settling rate

Cited by 65 publications

References 42 publications

The use of LDS as a tool to evaluate flocculation mechanisms

The use of LDS as a tool to evaluate flocculation mechanisms

Designing thickeners by matching hindered settling and gelled suspension zones in the presence of aggregate densification

Using Light Scattering to Screen Polyelectrolytes (PEL) Performance in Flocculation

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