Flocculation Of Clay Suspensions Research Articles

Flocculation of Clay Suspensions by Anionic and Cationic Polyelectrolytes: A Systematic Analysis

The characteristics of clayey suspensions, majorly composed of quartz microparticles, in the presence of anionic and cationic polyelectrolytes were investigated using different techniques. A wide range of clay concentrations was used, i.e., from 0.07 to 1000 g/L for different experimental techniques, based on the fact that the clay concentration possible to analyze with selected experimental methods was significantly different. The optimum flocculant to clay ratio was defined as the ratio that gives the fastest initial floc growth by static light scattering or fastest initial settling velocity by settling column experiments. In case of anionic polyelectrolyte, it was observed that the optimum flocculant dose depends on the amount of cations present in the system. For suspensions made with demi-water, a lower optimum flocculant dose (<1 mg/g) than for suspensions prepared in tap water (2.28 mg/g) was observed. At these lower salinities, the supernatant remained turbid in all the experiments and was, therefore, not a good measure for optimal anionic based flocculation. The equilibrium floc size at a given shear rate was found to be independent on the shear history of the floc and only dependent on the current applied shear. This was confirmed by both light scattering and rheological analysis. In case of cationic polyelectrolyte, the optimum flocculant ratio (5–6 mg/g) corresponded to the ratio that gives the lowest electrophoretic mobility for each clay concentration and to the ratio that gives the fastest settling velocity for the highest clay concentrations (12–15 g/L), where static light scattering measurements were not possible. All investigation techniques, therefore, proved to be good indicators for predicting the optimum flocculant to clay ratio. For the lowest concentrations (1.75–8.7 g/L) studied by settling column measurements, the optimum flocculant ratio was observed to increase with decreasing clay concentration, for fixed mixing conditions. The optimum flocculant to clay ratio was not always corresponding to the clearest supernatant and the size of flocs at optimum dosage was dependent on the mixing efficiency. The equilibrium floc size at a given shear rate was found to be dependent on the shear history of the floc and the current applied shear. This was confirmed by both light scattering and rheological analysis.

Influence of pH and ionic strength on flocculation of clay suspensions with cationic xylan copolymer

In this work, the influence of pH and ionic strength on the flocculation performance of cationic xylan copolymer in kaolin and bentonite suspensions was systematically investigated. The cationic xylan was produced via copolymerizing xylan with 2-(methacryloyloxy ethyl) trimethylammonium chloride (METAC), and the cationic xylan copolymer (CMX) showed a maximum adsorption of 4.6 and 1.8mg/g on kaolin and bentonite particles at the CMX dosage of 8mg/g, pH 10, 30°C and 1h, respectively. The reduction in charge density of CMX from 2.66 to 2.48meq/g was observed, with an increase in pH of CMX solution to from 2 to 10. The maximum increase in the zeta potential of kaolin (+54mV) and bentonite (−3mV) suspensions and the highest removal of kaolin (75%) and bentonite (96%) from the suspensions were obtained at 8mg/g CMX and pH 7. Stability studies revealed that pH had a noticeable influence on the sedimentation of kaolin and bentonite particles. CMX increased the destabilization index of kaolin (0.4–45) and bentonite (0.2–51) suspensions by increasing the floc size of kaolin and bentonite particles to 9.5μm and 12.7μm, respectively. CMX removed more of bentonite than kaolin at any pH under static and dynamic conditions. The impact of inorganic salts on the removal of kaolin particles was also studied. CMX exhibited better performance than a commercial flocculant (PDADMAC) in flocculating the commercially produced effluent.

セリシンによる粘土粒子の凝集に関する研究(第1報) : パイロフィライト,イライトおよびモンモリロナイトの電気泳動に及ぼすセリシンの影響について

セリシンによる粘土粒子の凝集に関する研究(第1報) : パイロフィライト,イライトおよびモンモリロナイトの電気泳動に及ぼすセリシンの影響について

Studies on flocculation of clay suspension by polyacrylamide

Abstract The flocculation of dilute pottery clay suspension using polyacrylamide (PAM) was investigated. Different molecular weight PAMs were synthesized by free-radical polymerization initiated with the persulfate-bisulfate redox pair. The synthesized polyelectrolytes (PAM1, PAM2 and PAM3, from low to high molecular weight) and a commercial one (C-492) were used for flocculation studies. The flocculating performance of polyelectrolytes was measured on 3% w/v pottery clay suspension using settling tests and turbidity measurements. PAM2 at pH 5.0 showed the maximum settling rate, which is nearly three times that of C-492, and it also showed a better turbidity reduction. Molecular weight is the key factor in influencing settling and turbidity reduction. In the present study, increasing molecular weight enhanced settling rate and turbidity reduction to a certain level beyond which there is a decrease, suggesting an optimum molecular weight for the given application. PAM2, a medium molecular weight polyelectrolyte (2.0·105 g/mol) has shown better performance than PAM1 (1.3·105 g/mol), PAM3 (6.0·105 g/mol) and the commercial polyelectrolyte C-492 (molecular weight of order 106).

Higher efficiency in the flocculation of clay suspensions by using combinations of oppositely charged polyelectrolytes

Abstract Dual systems—the highly charged polycation poly(diallyll-dimethyl-ammoniumchloride) (PDADMAC) in combination with different high molecular weight polyanions of the polyacrylamide type—were tested as flocculants for clay suspensions and natural waste waters from gravel pits. The flocculant performance was characterised by measuring the sedimentation behaviour as well as the residual turbidities and the extent of polymer adsorption. Whereas the molecular weight of the high molecular weight polycation is of lower influence, the removel of suspended particles is greatly affected by the molecular weight of the polyanion. Our experiments showed that degradation of the very high molecular weight polyanions leads to higher turbidity of the supernatant. The order of addition of the two polyelectrolytes influences the flocculation mechanism. Most effective is the addition of polycation followed by the polyanion. So a combination of patching and bridging is obtained.

The influence of silicic acid on aluminium hydroxide precipitation and flocculation by aluminium salts

Silic acid is always present in natural waters and interactions between silicic acid and aluminium have been reported over wide concentration ranges. Since aluminium salts are commonly used as coagulants in water treatment, it is possible that their effects may be modified by the presence of silicic acid. In many cases flocculation of particles in water is dependent on the formation of an amorphous precipitate of aluminium hydroxide and silicic acid may influence the precipitation process. Using a simple continuous optical technique, the influence of silicic acid on the precipitation process and on the flocculation of clay suspensions by aluminium sulphate has been examined. It has been found that silicic acid can promote or prevent the aggregation of primary aluminium crystallites depending on solution pH and the concentration of silicic acid. These effects are closely matched by the effect of silicic acid on the flocculation process. At pH 7, with about 0.3 mM of silicic acid, the growth of precipitate and flocculation are enhanced; but with higher silicic acid concentrations these processes are hindered and eventually prevented altogether (at around 1.5 mM). The effects of silicic acid are more pronounced at pH 8, where less than 0.1 mM is sufficient to enhance precipitation and flocculation, and at 0.25 mM they are completely inhibited. These trends have been confirmed by determining the residual turbidity of suspensions after a standard stirring and sedimentation procedure and by electrophoretic mobility measurements on particles shortly after dosing of coagulant. It appears that the effects are closely connected with silicic acid–aluminium interactions, especially with regard to modifications in the charge of precipitated species.

Effect of Interaction Between Clay Particles And Fe3+ Ions on Colloidal Properties of Kaolinite Suspensions

AbstractFine kaolinite suspensions were mixed with unaged or aged FeCl3 in this experiment. The interaction between clay particles and Fe3+ hydrolysis products was studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The proportion of Fe adsorbed was measured and the electrical charge on the clay particles was determined by electrophoresis. The effect of this interaction on flocculation of clay suspensions was investigated in a series of sedimentation tests. The Fe3+ ions acted as counterions when their concentration was low and when unaged FeCl3 solution was used. Otherwise, their hydrolysis complexes acted as a bonding agent between kaolinite particles. The dispersion-flocculation behavior of kaolinite suspensions was found to be in agreement with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO), as the sedimentation behavior could be predicted from the data of zeta potentials (ζ).

Flocculation of clay suspensions with water‐insoluble starch grafting acrylamide/sodium allylsulfonated copolymer powder

AbstractUse of water‐soluble and ‐insoluble starch grafting acrylamide/sodium allylsulfonated copolymers as flocculants to flocculate the clay suspension was investigated. The composition of acrylamide (AM), sodium allylsulfonated (SAS), and starch (St) repeating units in the water‐soluble and ‐insoluble starch‐grafted copolymer is about 0.718, 0.022, and 0.260 and 0.439, 0.014, and 0.547, respectively. For the water‐soluble starch‐grafted copolymer, the fast initial Ar decreasing rate and the lowest final Ar value occur at pH 2, 80 mg/L water‐soluble starch‐grafted copolymer and 100 mg/L clay suspension. As the suspension contains 1000 mg/L Na+ ion, the flocculating capability would be increased. For the water‐insoluble starch‐grafted copolymer, the initial Ar decreasing rate and the final Ar value are 1.6 times and 0.4 times, respectively, that of the water‐soluble starch‐grafted copolymer at the same test suspension. © 1995 John Wiley & Sons, Inc.

Flocculation of clay suspensions by an anionic soil conditioner

Ca- and Na-montmorillonite and Na-kaolinite were flocculated from suspension by two anionic soluble polymers. Light absorbance at 280 nm served as degree of flocculation measure. A prerequisite for flocculation was that salt concentration in clay suspension should exceed 1.0 and 0.2 meq. l −1 for Na- and Ca-montmorillonite, respectively. Furthermore it was shown that the clay had to adsorb a minimum amount of polymer: 0.8 mg/g for a 0.735 g l −1 Na-montmorillonite suspension and 1.0 mg/g for a 0.436 g l −1 Ca-montmorillonite suspension. Saturation adsorptions of polymers on Na- and Ca-clays were estimated to be 4.6 and 7.0 mg/g. These levels of adsorption stabilized the suspension and prevented flocculation. Na-polymetaphosphate (Calgon) added to a Na-montmorillonite suspension after the polymer addition retarded flocculation whereas its addition at a level >2.7 mg/g prior to the polymer addition prevented flocculation. Increasing the pH of the Na-kaolinite suspension from 6.5 to 8.2 considerably reduced its flocculation by the polymer. The effects of both pH and Na-polymetaphosphate indicate the importance of the positively charged sites on the clay in adsorption of anionic polymers and contribute to understanding of flocculation mechanisms.

Flocculation of clay suspensions separated from soils of different soil type

Abstract The critical coagulation concentration (c.c.c.) was measured for Na-saturated clay suspensions prepared from selected soils including Gray Lowland Soils, Yellow Soils, Red Soils, and Dark Red Soils by the addition of NaCl solution. A clear difference in c.c.c. was observed between the clays of Gray Lowland Soils and those of Red and Yellow Soils (Yellow Soils, Red Soils, and Dark Red Soils). The c.c.c. values for Gray Lowland Soils exceeded 2 me/dm3, whereas those for Red and Yellow Soils were for the most part less than 2 me/dm3. This difference was ascribed to differences in surface charge density. The value of 1 μe/m2 formed the boundary between the two groups. In each of the Gray Lowland Soils and Red and Yellow Soils, the clays containing smectite exhibited higher c.c.c. values than did the other clays.

Flocculation of Clay Suspensions in the Presence of Humic and Fulvic Acids

AbstractSurface waters which contain suspended clay and organic matter, differ strongly in response to flocculation from suspensions of “pure” reference clays in controlled systems. The mechanism of interference was investigated by means of a synthetic system, consisting of suspensions of reference clay with humic and fulvic acid added. These organic soil acids increase the colloidal stability of the suspension. Due to chemical reaction taking place between the organic acids and the cationic flocculant, higher flocculant doses were required in systems where interaction of clay and organic matter occurred.