The effects of cationic polymers on flocculation of a coal thickener feed in washery water as a function of pH

A flocculant based on cashew gum (CG) grafted with polyacrylamide (PAM) was synthesized using potassium persulfate as the chemical initiator and ultrasound energy. The intrinsic viscosity, hydrodynamic radius, and grafting efficiency of the grafted copolymers (CG-g-PAM) were investigated at different monomer and initiator concentrations. The CG-g-PAM copolymers were evaluated in kaolin suspension and river water by using jar test procedure comparatively to a commercial flocculant (Flonex-9045). Ultrasonication resulted in reduced reaction time and high grafting efficiency. The reaction gel point was reached within 10 min and the grafting efficiency was dependent on the acrylamide concentration. The grafted copolymer CG-g-PAM-15 285 obtained with 0.285 mmol of initiator showed higher hydrodynamic radius, with flocculation efficacy of 96% comparable with the flocculant Flonex-9045.

Section: Resultsmentioning

confidence: 99%

Chemical modification of cashew gum with acrylamide using an ultrasound‐assisted method

Klein

Lima

Feira

et al. 2016

“…Cationic starches, especially those with high DS, are the most common type of starch derivative flocculants investigated due to the efficient flocculation of anionic trash and produce a good settling performance for relatively low cost. Over the recent years many studies have been performed to examine flocculation behavior and to elucidate the interaction between cationic starch and substrate 5–15. All authors reiterated the point that the adsorption and flocculation processes must occur simultaneously to work and should not be thought of as separate mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Flocculation properties and adsorption kinetics of cationic starches in kaolin suspensions

Chen

Liu

Wang

2007

The flocculation characteristics of cationic starches with degree of substitution (DS 0.32-0.63) have been evaluated in 1.0 wt % kaolin suspension by spectrophotometry and colloid titration. Cationic starch is found to be an effective flocculant for removal of anionic suspension particles. Changes in the electrokinetics of kaolin as a function of pH were investigated in the absence of flocculant. The results show that kaolin in water exhibits a negative surface charge at pH > 2.5. The negative hydrophilic surface sites of kaolin are responsible for the adsorption of cationic starch molecules. The experimental data of the adsorption of cationic starch (DS 0.51) follow a Langmuir isotherm with maximum adsorption capacities of 16.89 mg/g. For the adsorption of cationic starch, chemical reaction seems significant in the rate-controlling step and the pseudosecond-order chemical reaction kinetics provides the best correlation for the experimental data.

“…It was only within a more or less narrow range of polymer/kaolin ratio where flocculation occurred and the polymer fulfilled his purpose as clarifying agent. Comparable flocculation curves have been obtained by other workers 6, 8, 15–22. While attempts were reported to define the point of optimum polymer dosage,7 a description of the flocculation performance including the limits of beginning flocculation and restabilization, based on plots such as shown in Figure 4, are commonplace in testing laboratories.…”

Section: Resultsmentioning

confidence: 71%

Chitosan‐graft‐acrylamide polyelectrolytes: Synthesis, flocculation, and modeling

Laue¹,

Hunkeler²

2006

A series of chitosans have been grafted with quaternary ammonium cationic monomers, as well as acrylamide using Ce(IV) to induce macroradical formation on the polysaccharide backbone. The materials, which have long chain branches per molecule between 0.3 and 5.5, are shown to provide very high specific flocculation efficiency, at the very least equal to the entirely synthetic materials which have been previously documented in the literature. A charge ratio, determined from the polymer concentration at which flocculation takes place, the charge density of the polymer, and the surface charge of the suspended matter are proposed as metrics to evaluate the occurrence of charge neutralization and bridging or charge patch flocculation mechanism. Furthermore, a window of application (WA) for flocculants, which characterizes the region of concentration wherein the polyelectrolyte can remove 99% of the supernatant turbidity, has been defined. It was shown to depend on the square root of the ionic strength and varies inversely with the Debye length, providing a fundamental basis for the concept of the WA. A mathematical expression is presented which links the WA with the salt concentration and the number of branches of the grafted polymer. Grafted chitosans have been shown to be more robust than polyacrylamides in testing against model kaolin suspensions.