Flocculation Of Suspensions Research Articles

Surface chemical properties and selective flocculation studies on alumina and silica suspensions in the presence of xanthan gum

The changes in the surface chemical properties of alumina and silica suspensions consequent to the addition of xanthan gum were studied. The adsorption density of xanthan gum for alumina was found to be maximum at pH 2, whereas nil adsorption was found for silica throughout the pH investigated. The isoelectric points (i.e.p.) of alumina and silica were found to be located at pH 9.1 and presumably less than pH 2 respectively. The addition of xanthan gum shifted the i.e.p. of alumina towards more acidic pH values, in proportion with the concentration of xanthan gum added, with a concomitant change in the zeta potentials to more electronegative or less electropositive values. The addition of xanthan gum beyond a certain concentration (>50ppm), increases the flocculation of alumina suspension to a higher value (∼92%), in the pH range of 2–9. The electrokinetic and flocculation characteristics of the silica were not altered much by the addition of xanthan gum, akin to the adsorption result. FTIR spectral investigations provide evidence in support of hydrogen bonding and chemical interaction forces between alumina and xanthan gum. Maximum separation efficiency of ∼93% for alumina-silica synthetic mixture was observed in selective flocculation tests.

Inferring in-situ floc size, predicting solids recovery, and scaling-up using the Leung number in separating flocculated suspension in decanter centrifuges

Abstract Centrifugation accompanied by flocculation of fine biosolids is often utilized in wastewater treatment. Unfortunately, commonly used laboratory jar tests often over-estimate the size of the flocculated solids (flocs) that can be realized in-situ in the centrifuge as the fragile flocs can be easily broken by shear and turbulence during feed acceleration in the centrifuge. Currently, there is no satisfactory method to predict in-situ floc size in the centrifuge, despite the floc size is critical to separation and solids recovery. The difficulty in making predictions also leads to inaccuracy in predicting solids recovery by decanter centrifuge and scale-up between centrifuges of different sizes, designs, and operating conditions, which is an even more serious issue. This study attempts to address these hurdles. In this study, first the flow pattern in a decanter centrifuge in form of moving layer at the pool surface is demonstrated by two different experiments. Second, a model on separation of suspended flocs in the moving layer in a centrifuge is developed. Further, a two-parameter model is proposed to represent the floc size distribution wherein the first parameter represents the minimum floc size (primary particle without coagulation or flocculation) and the second parameter represents the median floc size. A closed form analytical solution for the model is obtained with results expressed by the ratio of minimum-to-median floc size and a dimensionless Leung number which measures feed rate to the clarification rate of the centrifuge. Third, a Buckingham-π analysis has been conducted on separation in a moving layer under centrifugal field confirming these two governing dimensionless parameters can also be derived independently from the more basic dimensionless π groups. Fourth, by matching the solids recovery obtained from field tests with the model prediction, the median floc size can be inferred. In this matching process, the minimum floc size is assumed to be equal to the size of the primary, unflocculated solids. Fifth, four sets of tests (over 20 runs) have been carried out using two decanter centrifuges of different sizes and designs operating, respectively, under different pool depths, feed rates, polymer dosages and rotation speeds in a wastewater treatment plant processing mixed sludge with 48% primary sludge and 52% waste activated sludge. The median floc size inferred from the present method is in the range of 4–9 mm from the three series of tests (14 tests). The improved feed acceleration design with speed matching closely that of the rotating pool results in less pool turbulence, larger flocs, and lower polymer dosage (7 kg polymer/ton sludge); while the poorer feed acceleration with more pool disturbance from the under-accelerated feed results in smaller flocs, and higher polymer dosage (9 kg/t). Sixth, an important application of the model is to predict solids recovery using an estimated median floc size and this approach has predicted the solids recovery reasonably well on the fourth set of tests (9 tests). Seventh, the scale-up for predicting solids recovery of flocculated suspension from decanter centrifuges of different sizes, designs, and operating conditions has been demonstrated using the dimensionless Leung number and the minimum-to-median floc size ratio.

Optimization of coag-flocculation processes of a newly synthesized quaternized oil palm empty fruit bunch cellulose by response surface methodology toward drinking water treatment process application

An optimization of coagulation and flocculation of kaolin suspension by a newly synthesized quaternized oil palm empty fruit bunch cellulose denoted as a 9QC was investigated using the central composite design of the response surface methodology. The influences of coag-flocculant dosage, pH, and kaolin suspension on turbidity removal efficiency and sludge volume index responses were studied and assessed according to a 23 full factorial design. The developed quadratic models revealed that the overall optimum values to obtain the highest performance of the responses were 62.5 mg/L of coag-flocculant dosage, pH 7, and 1400 mg/L of kaolin concentration. The predicted optimum responses were found to be in close proximity to the observed responses. The coag-flocculating of river water using 9QC carried out at the optimum values showed encouraging results as compared to alum which is commonly used in drinking water treatment process.

Ultraviolet-assisted synthesis of polyacrylamide-grafted chitosan nanoparticles and flocculation performance

In the present work, a new flocculant, polyacrylamide-grafted chitosan nanoparticles (NCS-g-PAM), was synthesized by the copolymerization of acrylamide (AM) and chitosan nanoparticle (NCS) under ultraviolet irradiation using 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone as photo-initiator. The NCS was prepared by the ionic gelation between chitosan and sodium tripolyphosphate. The structure and morphology of NCS-g-PAM were characterized by Fourier Transform Infraredspectroscopy (FT-IR), X-ray diffraction, 1H-nuclear magnetic resonance spectrometry, scanning electron microscopy, and thermogravimetric analysis. The factors affecting the intrinsic viscosity and the yield of copolymer were studied, which showed that the optimum conditions for the synthesis of NCS-g-PAM were mAM:mNCS=8:1, 0.15g of initiator dosage, mCS:mTPP=4.5:1, 1min of ultrasonication time, 4h of illumination time, and 30min of stirring time. The NCS-g-PAM was found to be more effective than NC-g-PAM in the flocculation of both kaolin suspension and Cu2+ simulated wastewater. With 5mg/L of polyaluminium chloride (PAC) coordinated and 1mg/L of NCS-g-PAM it was confirmed to be appropriate for flocculating kaolin suspension.

Role of cationic polarization in humus‐increased soil aggregate stability

It is well known that humus markedly increases soil aggregate stability, but at the same time strongly decreases the flocculation of clay particles in suspension. These seemingly inconsistent observations suggest the need for a deeper understanding of the physical mechanisms that govern clay–humus interactions. In this research, soil samples from an Entisol were used to explore the role of cationic polarization in humus‐increased soil aggregate stability and sodium (Na+) and potassium (K+) ions were used to characterize weak and strong polarization, respectively. The results showed that strong cationic polarization has a critical role in increased soil aggregate stability in the presence of humus. We concluded that, without cationic polarization, the effects of humus alone on soil aggregate stability were weak in the presence of monovalent metal cations. When we compared the individual contributions of humus and strong cationic polarization, the latter proved much more important than humus in increasing soil aggregate stability. The strongest increase in soil aggregate stability occurred when strong cationic polarization was coupled with humus. The combined analysis of activation energy of soil flocculation in suspension and soil aggregate stability in the presence of humus indicated that humus increased the long‐range electrostatic repulsive force of soil particles, and increased the short‐range attractive force of soil particles. Consequently, humus decreased the flocculation of soil particles in suspension but increased soil aggregate stability; all effects were adjusted by the strength of cationic polarization.Highlights Elucidation of physical mechanisms of cation–surface interactions that determine clay–humus interactions. Cations at the particle surface of the clay–humus complex are strongly polarized. Cationic polarization has a critical role in humus‐increased soil aggregate stability. Without cationic polarization, the effect of humus alone on soil aggregate stability was weak.

Preparation and flocculating properties of highly substituted cationic starches of different vegetable origins

Kinetic regularities of flocculation of model kaolin suspensions by highly substituted cationic flocculants synthesized from different starches (corn, waxy corn, potato, and tapioca starches) have been studied as depending on the doses and vegetable origins of the flocculants. The rate of kaolin suspension flocculation has been found to increase with the dose of the cationic starches of all types. It has been shown that, irrespective of the dose, the highest rate of kaolin sedimentation in the model systems is observed in the presence of cationic potato starch. It has been demonstrated that cationic potato starch flocculates kaolin suspensions with concentrations of 0.1, 0.5, and 1.0% with the same efficiency. In this case, the suspensions are almost completely clarified within 2–5 min. Moreover, the dependence of the flocculating efficiency for a 0.1% model suspension on the dose of cationic starch has been found to pass through a maximum at a starch content of 1.0–5.0 mg/g of kaolin depending on the type of starch.

Flocculation of fine hematite and quartz suspensions with anionic cellulose nanofibers

Research was undertaken to investigate the efficiency of anionic dicarboxylic acid (DCC) and sulfonated (ADAC) cellulose nanofibers in flocculating fine hematite and quartz particles. Flocculation was studied at pH levels varying from 5 to 10 and chemical dosages of 0–2000ppm, with turbidity measurements after sedimentation and with analytical centrifugation after a short intense mixing stage. Results showed that DCC and ADAC cellulose nanofibers did not flocculate quartz within pH range 5–10 but were able to flocculate hematite. DCC's ability to flocculate hematite and the ability of formed flocs to withstand the shear forces of subsequent intense stirring depended markedly on the pH of the suspension. The most effective performance was obtained at a pH of 8–9, and a DCC dosage of 200–500ppm was enough to flocculate hematite efficiently. In addition, unlike ADAC nanofibers, DCC nanofibers were able to flocculate hematite under short vigorous stirring. ADAC nanofibers proved to be as efficient a hematite flocculant as DCC nanofibers at a dosage of 500ppm after longer conditioning time and less vigorous stirring. Furthermore, the operational pH region was wider for ADAC nanofibers, and the hematite flocs did not show any pH-dependent breakage.

Transient viscosities of negatively buoyant concentrated alumina suspensions

AbstractThe transient viscosities of sterically stabilized alumina suspensions with different degrees of aggregation were measured at low viscous flows in a Couette viscometer. The well‐dispersed suspensions showed an increase in viscosity under a constant applied shear while the flocculated suspensions showed just the opposite behaviour. The drifts in the viscosity of the well‐dispersed suspensions show strong features of shear‐induced particle migration. However, experimental observations strongly indicate that the observed viscosity profiles of these suspensions are resultant of the competitive processes of shear‐induced particle migration and shear rejuvenation. The drifts in viscosity of the well‐dispersed suspension could be correlated to the degree of aggregation present in the suspension. On the other hand, the viscosity profiles of the flocculated suspensions showed characteristic shear rejuvenation behaviour. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd.

Cationic xylan–METAC copolymer as a flocculant for clay suspensions

The work presented herein focused on the flocculation of kaolin and bentonite clay suspensions using cationic copolymerized xylan under controlled conditions.

Temperature- and pH-Responsive Benzoboroxole-Based Polymers for Flocculation and Enhanced Dewatering of Fine Particle Suspensions.

Random copolymers based on N-isopropylacrylamide (NIPAAm) containing 2-aminoethyl methacrylamide hydrochloride (AEMA) and 5-methacrylamido-1,2-benzoboroxole (MAAmBo) were synthesized and subsequently evaluated for their performance in solid-liquid separation at various pH and temperatures. The strong interactions between benzoboroxole residues and kaolin hydroxyl groups were evaluated for the first time in the flocculation of fine particle suspensions. The lower critical solution temperatures (LCSTs) of PAMN decreases because of the hydrophobic nature of the benzoboroxole moieties, resulting in strong hydrophobic interaction at temperatures higher than the LCSTs. Temperature and pH responsive polymer, P(AEMA51-st-MAAmBo76-st-NIPAM381) (denoted as PAMN) shows the ability to induce fastest settling at a low dosage of 25 ppm and under the condition of pH 9 and 50 °C. The accelerated settling rate is considered to be due to the strong adhesion of benzoboroxole residues to the kaolin hydroxyl groups, the electrical double layer force, and the hydrophobic force. During condensation phase, increasing the pH of sediment to pH 11 could attain the most compact structure. Random copolymers containing benzoboroxole groups act as dispersants (due to pH-responsive character) rather than flocculants at pH 11, providing repulsive force that enables particles to rearrange their position and consolidate well. Through a two-step solid-liquid separation including settling phase and consolidation phase, rapid settling and compact sediment are feasible simultaneously.

On the Trail of Better Dispersion: Rheological Characterization of Moderately Loaded, Finely Balanced, Negatively Buoyant Ceramic Suspensions

ABSTRACTThis work aims at finding the best dispersion in a series of alumina suspensions stabilized with the help of different dosages of an electrosteric dispersant phosphate ester. Time dependent viscosities of these suspensions were measured with the help of a conventional Brookfield viscometer at low shear rate domain of 1–8 sec–1. Sedimentation tests, microscopic observations and gloss value measurement show that some of these suspensions are well-dispersed and some of them are flocculated. Time dependent viscosity measurements for all the well-dispersed suspension and a flocculated suspension were carried out in a conventional Brookfield viscometer. Interestingly, all the well-dispersed suspensions show positive drifts in viscosity with time at a constant shear; however, the magnitude of drifts differed for these suspensions. Rheological measurements show strong evidences of shear induced hydrodynamic migration occurring under the action of the applied shear rates for the well-dispersed suspensions. On the other hand, the flocculated suspensions show just the reverse behavior. Application of short-time shear ramp and long-time shear ramp on the well-dispersed suspensions shows interesting variations. ESA studies conducted for these suspensions showed strong signatures of varying particle sizes for each of these suspensions. The present investigation shows strong indication that the physics behind shear induced diffusion may be utilized to characterize and identify the best dispersion in a series of finely balanced negatively buoyant particulate suspensions by studying the time-dependent viscosities of these suspensions under low shear conditions.

Isolation and characterization of a bioflocculant from Bacillus megaterium for turbidity and arsenic removal

A biodegradable flocculant was produced during growth of Bacillus megaterium. The major component of the bioflocculant was found to be a polysaccharide composed of some proteins. Fourier transform infrared (FTIR) spectra analysis revealed the presence of carboxyl and hydroxyl groups in the bioflocculant, and thermal characterization by differential scanning calorimetly (DSC) showed the transition and crystalline melting point at 90-105 degrees C. The effects of bioflocculant dosage and pH on the flocculation of mineral suspensions were evaluated. The bioflocculant exhibited good flocculating capability on mineral suspensions and achieved flocculating efficiencies of 90 percent for k-aolinite and 85 percent for hematite suspensions at a dosage of only 5 mL/L. The maximum arsenite removal was found to be 90 percent at a bioflocculant dosage of 2 g/L, which is better than traditional chemicalflocculants. This study demonstrates that microbial bioflocculants have potential for application in environmental cleanup, such as in the flocculation of mineral fines and in the remediation of solutions that contain toxic heavy metals.

Effects of Polymer Molecular Weight on Adsorption and Flocculation in Aqueous Kaolinite Suspensions Dosed with Nonionic Polyacrylamides

The effects of polyacrylamide (PAM) molecular weights (MWs) on the PAM adsorption capacities and PAM-mediated flocculation of kaolinite suspensions were investigated using a series of nonionic PAMs with different MWs. Adsorption tests using aqueous kaolinite suspensions dosed with a series of PAMs with MWs of 1.5 kg/mol, 10 kg/mol, 0.6–1 Mg/mol, 5–6 Mg/mol, and 18 Mg/mol (referred to as 1.5 K, 10 K, 0.6–1 M, 5–6 M, and 18 M PAMs) indicated that the adsorption capacity of the kaolinite for PAM increased with increasing MW. However, the capacity for 18 M PAM was 20 times smaller than those for the 0.6–1 M and 5–6 M PAMs, although it has the highest MW. In steady-shear viscosity tests, a 1 g/L stock solution of 18 PAM was found to cause polymeric chain entanglements, which reduced the adsorption capacity. The 0.6–1 M and 5–6 M PAMs were further used in flocculation tests, in order to investigate the effect of PAM MW on the flocculation capability. The 5–6 M PAM was found to have higher flocculation capabilities than 0.6–1 M PAM; 5–6 M PAM was more subject to nonequilibrium flocculation, resulting in the development of unstable, stretched polymeric structures on solid surfaces and increasing particle-particle bridging and flocculation. Higher-MW PAMs are more effective flocculation agents, because of their higher adsorption capacities and flocculation capabilities. However, an extremely high-MW PAM, such as 18 M PAM, decreases adsorption/flocculation, and the preparation and handling of working solutions become difficult, because of polymeric chain entanglements.

Flocculation and viscoelastic behavior of industrial papermaking suspensions

The effects of the surface charge type and density C496, C492 and A130LMW polyacrylamides (PAMs) on the rheological behavior of real industrial papermaking suspensions were quantitatively related to the degree of flocculation for the same industrial papermaking suspensions. The floc sizes were larger but less dense when anionic PAM was used, and this due to the repulsive forces between the anionic PAM and colloidal particles, leading to the development of open structure flocs of less density. On the other hand, rheological measurements showed that the papermaking suspension is thixotropic with a measurable yield stress. The results showed that the magnitude of the critical stress, τ c , complex viscosity, η*, elastic modulus, G′, and viscous modulus, G″, depend on the number of interactions between the PAM chains and particle surface and the strength of those interactions. Cationic PAM showed higher values of η*, G′, G″ and τ c compared to anionic PAM. This behavior is in good agreement with Bingham yield stress, τ B , adsorption and effective floc density results. Similar to oscillatory measurements, creep measurements also showed that the deformation was much lower for the cationic PAM based suspensions than for the anionic PAM based suspensions. Furthermore, the results revealed that increasing the cationic PAM surface charge decreases the floc size but increases the adsorption rate, elasticity and effective floc density proposing differences in the floc structures, which are not revealed clearly in the Bingham yield stress measurements.

Flocculation of coal suspension with mono/dual polymer systems and contribution of Ca(II)/Mg(II) ions

In the experimental study carried out on mono-flocculation, anionic and especially non-ionic polymers strongly flocculated the coal suspension than cationic polymer. The dual-flocculation of the coal suspension with cationic and anionic polymer combination was also studied and the high performances of flocculation were also reached with dual-polymer approach. Furthermore, dual-polymer system required lower concentrations for the successful flocculation of coal particles. On the other hand, the pre-destabilization of the coal suspension with calcium and magnesium ions at particular pH and concentrations highly improved the flocculation of fine coal particles with these polymers.

Hydrophobic flocculation of talc with kerosene and effects of anionic surfactants

ABSTRACTThe variation of the hydrophobic flocculation behavior of talc mineral with pH, kerosene concentration, stirring speed, flocculation, and settling times was investigated. The experimental studies showed that the flocculation of talc suspension increased to a particular point with increasing kerosene concentration and thereafter decreased slightly. Also, the flocculation with kerosene was not much affected by the pH changes of the suspension. On the other hand, sodium oleate, sodium dodecyl sulfate (SDS), and Aero 801 used as anionic surfactant in conjunction with kerosene provided significant increases in the flocculation of talc, and depends on increasing surface hydrophobicity of the particles. Especially, in the presence of sodium oleate along with kerosene, the talc suspension could be flocculated with a recovery of 95%. Consequently, the enhancement with nonpolar oil was more significant for the hydrophobic flocculation of talc suspension promoted by long hydrocarbon chain surfactant (sodium oleate) than short hydrocarbon chain surfactants (SDS and Aero 801).

Synthesis and flocculation characteristics of a novel biodegradable flocculating agent amylopectin-g-poly(acrylamide-co-N-methylacrylamide)

Abstract Amylopectin-g-poly(acrylamide-co- N -methylacrlymide) [AP-g-poly(AM-co-NMA)] was prepared in presence of potassium persulfate (K 2 S 2 O 8 ) as the initiator by solution polymerization technique. The synthesised graft copolymer was characterized by various characterization techniques like FTIR, 1 H NMR and 13 C NMR spectroscopy, thermal analysis and SEM. Biodegradation of the graft copolymers was carried out by enzyme hydrolysis. Flocculation performance of the graft copolymer was evaluated in 1.0 wt% coal, 1.0 wt% silica, 1.0 wt% kaolin, 0.25 wt% iron ore and 1.0 wt% bentonite clay suspensions. The flocculation efficiency of the graft copolymer was also evaluated by the colour removal capacity from aqueous solution of a synthetic dye, malachite green. A comparative study of the flocculation performance AP-g-poly(AM-co-NMA) was also made with another laboratory synthesised graft copolymer namely amylopectin-g-polyacrylamide (AP-g-PAM) and some commercially available flocculants in the same suspensions and also in the malachite green solution. The results showed that the graft copolymer AP-g-poly(AM-co-NMA) showed better flocculation performance than that of AP-g-PAM as well as to some of the commercial flocculating agents.

A non-linear viscoelastic model for sediments flocculated in the presence of seawater salts

A new empirical three-parameter viscoelastic model is proposed for describing the rheological behavior of linear and nonlinear materials. In particular, the model succesfully reproduced experimental creep curves at various constant stresses for flocculated suspensions of alumina in the presence of different types of seawater salts. The new model is compared to the classical standard linear solid model and to an extension of this, also proposed here, to represent nonlinear materials. Based on the goodness of fit, the new model is found to be the most appropriate for the experimental system studied. A sensitivity analysis of the parameters to applied stress and type of salt in the sediments reveals that the new model, originally proposed as an ansatz, has three components, constant, linear and nonlinear, as inferred from the behaviour of each model parameter with the applied stresses. The linear contribution follows a correlation with the applied stresses for salts that enhance the hydrogen network of water, so called maker salts, and another for the salts that weaken the network, so called breaker salts. Even more interesting, the nonlinear contribution is characterized by large exponential decay lengths for breaker salts and small exponential decay lengths for maker salts. The existence of linear and nonlinear components may enable applying the model to a variety of systems.

The new effective flocculants – Copolymers of N,N-dimethyl-N,N-diallyl-ammonium chloride and N,N-dimethylacrylamide

Radical copolymerization of N,N-dimethyl-N,N-diallylammonium chloride (DMDAAC) with N,N-dimethylacrylamide (DMAA) has been investigated by FT-IR, 1H NMR spectroscopies, conductometric and turbidimetric titration methods. Flocculation of bentonite suspensions, pig, chicken and cow manure slurries were investigated using the copolymer P(DMDAAC-DMAA) with various compositions and homopolymer P(DMDAAC) by turbidimetric method and the zeta potentials of each samples were tested. The results indicated that copolymer P(DMDAAC-DMAA) (with molar composition 70:30) has the best flocculating ability compared to the other compositions and homopolymer P(DMDAAC). Compared to four suspensions pig manure was found to be more difficult to settle down.

Characterization and flocculation mechanism of a bioflocculant from potato starch wastewater.

This study investigated the characterization and flocculation mechanism of a bioflocculant prepared using potato starch wastewater. The optimal culture conditions of this strain were determined as 4 g K2HPO4, 2 g KH2PO4, 0.2 g MgSO4, 0.1 g NaCl, and 2.0 g urea dissolved in 1.0 L potato starch wastewater with no need of adding carbon sources or adjusting pH value. Production of this bioflocculant was positively associated with cell growth, and a highest value of 0.81 g/L was obtained. During the kaolin suspension flocculation, charge neutralization and interparticle bridging were proposed as the main reasons for enhanced performance. Further, with potato starch wastewater, chemical oxygen demand (COD) and turbidity removal rates reached 52.4 and 81.7 %, respectively, at pH 7.5 when the bioflocculant dose was adjusted to 30 mg/L.