Flocculation Concentration Research Articles

Flocculation of Whey Protein Stabilized Emulsions as Influenced by Dextran Sulfate and Electrolyte

ABSTRACTThe creaming stability and viscosity of oil‐in‐water emulsions stabilized by whey protein isolate were monitored as functions of dextran sulfate (DS) and electrolyte (NaCl) concentration. At a specific DS concentration (the critical flocculation concentration, CFC), the droplets became flocculated, which promoted creaming. Addition of electrolyte caused an increase in CFC. At NaCl concentrations <0.5 wt%, addition of electrolyte decreased emulsion viscosity, but at concentrations >0.5 wt% it caused an increase in viscosity due to increased flocculation. The results were due to the influence of electrostatic screening on the effective volume of DS molecules and colloidal interactions between droplets.

Self-Assembled Monolayer of Sugar-Carrying Polymer Chain: Sugar Balls from 2-Methacryloyloxyethyl d-Glucopyranoside

A sugar-carrying polymer chain with a disulfide group (DTPA−PMEGlc) was prepared by the coupling of poly(2-methacryloyloxyethyl d-glucopyranoside) (PMEGlc), which carried an amino group at its end, with 3,3‘-dithiodipropionic acid di-p-nitrophenyl ester. The polymer obtained was incubated with colloidal silver, and a self-assembled monolayer (SAM) of the polymer chain (PMEGlc) was formed on the surface of the colloid as evidenced by surface-enhanced Raman spectroscopy, cyclic voltammetry, dynamic light scattering, and ellipsometry. The silver colloid was largely stabilized by the modification with PMEGlc chains due to the formation of a thick diffuse layer on the surface. The critical flocculation concentration (CFC) of the modified colloid was not detectable, which is a contrast to the presence of CFC for the starting silver colloid dispersion (0.1 M NaCl at 25 °C). The polymer-coated colloids obtained (“sugar balls”) were aggregated when a solution of lectin (concanavalin A (Con A) from Canavalia ensifo...

Multilayer Deposition of Stable Colloidal Particles during Flow within Cylindrical Pores

Multilayer deposition of stable colloidal particles during the low Reynolds number flow of aqueous suspensions of latex particles through cylindrical pores in track-etched membranes has been experimentally studied. Though multilayer deposition or the role of deposited particles as additional collectors has been recognized before this work, the reason multilayer deposition of particles occurs in the presence of strong interparticle repulsion and the interactions governing the transition from single layer to multilayer deposition have not been elucidated. Because sufficient repulsion exists between particles in a stable suspension to prevent their aggregation by Brownian flocculation, the deposition of particles on top of previously deposited particles to form multilayers is flow-induced. In this paper, we first show that only a single layer of particles will be deposited on the pore surface if strong repulsion exists between particles. We then demonstrate the transition from single layer to multilayer deposition at a sufficiently high flow rate when the interparticle repulsion is reduced by adding an electrolyte (but not exceeding the critical flocculation concentration). Under these conditions, the hydrodynamic force acting on a flowing particle in the vicinity of a deposited particle can overcome the net interparticle repulsion and multilayers of particles can accumulate within the pores. Approximate calculations of the trajectory of a flowing particle in the vicinity of a stationary particle that qualitatively demonstrate the flow-induced nature of the phenomenon are also presented.

Estimation of the wettability of coal from contact angles using coagulants and flocculants

The effect of electrolyte coagulants and flocculants on coal surface properties was investigated through measurements of contact angles and zeta potentials at various amounts of reagents and pH values. Results obtained show that maximum contact angles for the coals studied occur in the alkaline pH range (pH > 7) for the conditions invetigated. Contact angles increased up to coagulant and flocculant concentrations of about 60 and 80 ppm by weight, respectively, and thereafter remain almost constant at higher concentrations. These studies indicate that the adsorption of flocculants occurs through physical interaction with the coal surface, possibly due to hydrophobic bonding, while the adsorption of coagulants could be attributed to hydrogen bonding. Coagulants probably affect flotation of coal fines adversely, whereas flocculants have a remarkable effect on contact angles similar to that of surfactants.

Flocculation of haematite in synthetic Bayer liquors

A simple turbidimetric method has been established for measuring the concentration of polyacrylate flocculants in synthetic Bayer liquors, as low as 0.5 μg g −1. It has been used to determine the isotherm of a polyacrylate flocculant from synthetic Bayer liquor onto the surface of a well characterised haematite. The polyacrylate flocculant was found to adsorb strongly on haematite in synthetic Bayer liquor with a plateau coverage of 164 μg m −2, contrary to previous belief that the presence of dissolved Ca 2+ is essential for bonding to occur under highly caustic conditions. It was calculated that at the plateau coverage the polyacrylate flocculant occupied less than 15% of the haematite surface, which may be indicative of a low number of active adsorption sites. Settling tests combined with the isotherm data showed that the mechanism of aggregation is bridging flocculation, with optimum performance obtained at a dosage corresponding to 20% of the plateau coverage.

Measuring the Stability of Disperse Systems

Hydrophobic sols such as silver iodide sol, silica sol, metal oxide sol, and others are very sensitive to inorganic salts; the addition of relatively small amounts of a salt can cause them to flocculate. The concentration of a salt required to flocculate the sol is called the critical flocculation concentration (CFC) or critical flocculation values (C CFC). Its C CFC is an important measure of the stability of a hydrophobic sol.

Stability behavior of soil colloidal suspensions in relation to sequential reduction of soils

The electrokinetic behavior of colloidal particles in three waterlogged soils at 38°C was investigated with reference to the stability changes of soil colloidal suspensions under reductive conditions. The dispersed clay particles of the three soils exhibited a negative zeta (ζ) potential. The absolute value of the ζ-potential, |-ζ|, of these soils in the earlier period of waterlogging decreased, which caused the flocculation of clay particles. The concentrations of divalent cations, i.e., Fe2+ and Ca2+ in the soil solutions were estimated to be higher than their critical flocculation concentrations (CFCs) on the basis of the observed CFCs of Fe2+ and Ca2+ for the clay suspension of halloysite as a reference. With the progression of the reduction process, clay particles of one soil still exhibited a low |- ζ| and flocculated. The concentrations of Fe2+ and Ca2+ in the soil solutions were estimated to be higher than their CFCs, respectively. The clay particles of two sandy soils, however, showed an increase in |- ζ| due to the increase in pH and dispersed. The concentrations of Fe2+ and Ca2+ in the soil solutions were estimated to be lower than their CFCs, respectively. The stability changes of the soil colloidal suspensions by these divalent cations under sequential soil-reduction can be explained by the alteration of the Stern potential (- ψ s ), which determines the repulsion energy related to the potential energy of interaction between two particles. The apparent decrease in the Ca2+ concentration of the soil solutions in the later period of waterlogging was explained largely by the re-adsorption of water-soluble Ca2+ on the exchange sites of soil clays with the decrease in the Fe2+ concentration in the soil solution.

Dextran stabilized poly(methyl methacrylate) latex particles and their potential application for affinity purification of lectins

Stable poly(methyl methacrylate) latex particles (220–360 nm in diameter) using dextran as the protective colloid were prepared and characterized in this study. Such an emulsion polymerization system follows Smith-Ewart Case III kinetics (i.e., the average number of free radicals per particle is greater than 0.5) due to the relatively large latex particle size. The carbohydrate content of these dextran modified emulsion polymers shows a maximum around 5% dextran based on total monomer weight. The latex stability during polymerization is closely related to the carbohydrate content of these latex particles, and it is controlled by the ratio of the thickness of the dextran adsorption layer to that of the electric double layer of the latex particles. The critical flocculation concentration (CFC) of the latex products correlates well with the latex stability during polymerization. The greater the total scrap produced during polymerization (i.e., the stronger the bridging flocculation), the lower is the CFC of the latex products. The affinity precipitation of concanavalin A (a model lectin used in this study) by the dextran modified PMMA latex particles is also illustrated in this study. The specifically adsorbed concanavalin A increases with the carbohydrate content of the dextran modified latex particles.

Effect of Nonadsorbing Polyelectrolytes on Colloidal Interactions in Aqueous Mixtures

The effect of adding a nonadsorbing charged polymer, sodium polystyrene sulfonate (SPSS), on the interaction energy profile between a 15 μm diameter polystyrene particle and a glass plate was measured using the optical technique of total internal reflection microscopy. A typical profile consisted of a repulsive barrier at large separations followed by a secondary well. Evidence of a longer-range tertiary well was also observed in salt-free solutions where the polymer molecules are rod-like. Addition of electrolyte causes a reduction in the depth of the tertiary well and produces oscillations at large separations. In addition, the stability of a solution of charged polystyrene particles in the presence of SPSS was measured using optical light scattering. Because of the electrostatic repulsion between the particles, the solution was stable against primary flocculation with no added polymer. However, because of long range attractive depletion forces, reversible secondary flocculation occurred into a local potential energy minimum at low SPSS concentrations (order 0.2 wt%). The polymer caused flocculation at a critical flocculation concentration (v*) which was found to decrease with increasing particle size. No restabilization of the latex dispersions was observed.

Measurement of Colloidal Stability in Solutions of Simple, Nonadsorbing Polyelectrolytes

The stability of a solution of charged polystyrene particles in the presence of nonadsorbing polyelectrolyte macromolecules is measured using optical light scattering. The particles were negatively charged polystyrene latex spheres (0.5–1 μm diameter) while the macromolecules were simulated using negatively charged colloidal silica spheres (5–7 nm diameter). Because of the electrostatic repulsion between the particles, the solution is found to be stable against primary flocculation (irreversible flocculation into a primary energy minima). However, because of long-range attractive depletion forces, reversible secondary flocculation of the particles occurs into a local potential energy minimum. As observed with uncharged macromolecules, the polyelectrolyte first induces flocculation at a critical flocculation concentration (v*), but later restabilizes the system at a critical restabilization concentration (v**). These critical concentrations are found to decrease with decreasing macromolecule size and increasing particle size. The restabilized solutions are found to remain suspended for periods greater than 20 days. Comparison of the measured flocculation and restabilization results to predictions made using a recently developed force-balance model show qualitative agreement.

Influence of adsorbed polymers on the removal of mineral particles from a planar surface

Experimental results on the role of adsorbed polymers on the particle adhesion are presented. Both Brownian (silica particles) and non-Brownian (glass beads) particles were used. The particles were deposited onto the internal surface of a glass parallelepiped cell, and then submitted to increasing laminar flow rates. The pH and the ionic strength of the electrolytes were fixed. The adhesive force was related to the hydrodynamic force required to dislodge 50% of the initially attached beads. We found that high molecular weight PEO had little effect on the adhesion of small silica beads due to the low affinity of the polymer for silica or glass surfaces. On the contrary, PEO greatly enhanced the adhesion of bigger glass beads forced to deposit on the capillary surface because of gravity. The increase was all the more pronounced as the molecular weight of the polymer was high. The effect of high molecular weight cationic copolymers on the adhesion of silica particles was drastic. The maximal force (1500 pN) applied by the device could not enable any particle detachment even using polymers of low cationicity rate (5%), showing the efficiency of electrostatic attractions. When copolymers were adsorbed on both surfaces (particles and plane), the adhesive force exhibited a maximum at intermediate coverage of particles. This optimum was related to the optimum flocculation concentration classically observed in flocculation of suspensions by polymers.

Characterization of carboxylated poly(butyl acrylate) latices produced by a semibatch process

Several carboxylated poly(butyl acrylate) latices prepared by a semibatch emulsion poly-merization process were characterized in this study. A significant amount of polyelectrolyte was found in the latex product containing 10% AA, designated as AA10. On the other hand, latices containing 0.1% AA (AA0.1), 0.1% MAA (MAAC.1), and 10% MAA (MAA10) showed very low levels of polyelectrolyte in water. Based on the critical flocculation concentration data, it can be concluded that incorporation of 10% AA or 10% MAA into the emulsion polymers can greatly improve the chemical stability of the latex products, especially at higher pH. The data of the pH and conductometric titration experiments show that the MAA unit can be distributed more uniformly in the latex particles in comparision with the AA unit. This result is further confirmed by determination of the Tg's of the emulsion polymers by means of thermally stimulated current (TSC). © 1996 John Wiley & Sons, Inc.

Flocculation and Stabilization of Allophane in the Presence of an Anionic Microbial Polysaccharide (Gum Xanthan) and Several of Its Hydrolytic Intermediates

Abstract The polymeric effect of gum xanthan (GX) on the stability of allophane at pH 4.5 and 6.5 was compared with the effect of several of its hydrolytic intermediates (hGX). The polymeric effect of GX was manifested by (i) the effective flocculation at low GX concentrations, (ii) the higher stabilizing ability above the flocculation concentration (FC), and (iii) the appreciable ability of deflocculation of (a) flocculated allophane and (b) allophane-halloysite floc, at extremely low concentrations of GX solution at pH 6.5. In contrast to GX, in the presence of sodium polyacrylate, there was a complete lack of deflocculation of the flocculated allophane at pH 6.5. This fact suggests that effective deflocculation is due to the double-stranded wormlike structure of the GX chain with a small but finite flexibility. The fact that flocculated allophane by GX at pH 4.5 still exhibited a positive electrophoretic mobility can be ascribed to the flocculation of allophane particles by bridging with this biopolyme...

Shear-induced flocculation: The evolution of floc structure and the shape of the size distribution at steady state

The flocculation of polystyrene particles in a stirred tank was studied at various shear rates (63–129 s −1) and aluminum sulfate, Al 2(SO 4) 3 16H 2O, flocculant concentrations. The competition between coagulation and fragmentation during shear-induced flocculation determined the equilibrium or steady state particle (floc) structure and size distribution. The evolution of the floc structure with time was monitored by image analysis of digitized floc images. The average floc structure became less open or irregular as the floc size distribution attained steady state as a result of shear-induced breakage/restructuring. At high alum (flocculant) concentrations, the steady state floc size distribution appeared to be self-preserving with respect to shear rate. In contrast, at lower flocculant concentrations, the steady state floc size distribution narrowed with increasing shear rate as the large tail of the distribution was pushed to smaller particle sizes by shear-induced fragmentation.

The investigation of the advanced treatment of municipal wastewater by modular flotation-filtration systems and reuse for irrigation

The objective of this study was to provide clarified municipal wastewater effluent at the turbidity level of less than 2.0 NTU and reuse for landscape irrigation (golf course). For that purpose, during pilot -study first was used a combined flotation-filtration module-clarifier alone (Alternative I). A particularly designed configuration of the primary flotation unit and combined flotation-filtration clarifier, as a modular clarification system was used in the next step of the investigation (Alternative II). In addition, start up of the full scale plant was performed as well. In the first phase of this study, the impact of the type and concentration of coagulant and flocculant was tested. As a result, mechanisms of flocculation were proposed. Only under the moderate hydraulic loads (75.7-151.4 LPM) during pilot tests by Alternative I, was it possible to reach satisfactory turbidity reduction. By the Alternative II, the clarification performance was improved under the higher hydraulic load (302.8 LPM). The kinetics of the investigated flotation systems were assesed by empirical flotation models. Based on the pilot-study, Alternative II is recommended in order to reduce the high solids loadings under a higher hydraulic load, and it provided irrigation water at a required rate of 3785 m3/d during start up and optimization of the full scale plant.

Separating oil from oil-water emulsions by electroflotation technique

The separation of finely dispersed oil from oil-water emulsions was carried out in an electroflotation cell which has a set of electrodes, a lead anode and stainless steel screen cathode. The effect of operating parameters on the performance of the batch cell was examined. The parameters investigated are electrical current, oil concentration, flotation time and flocculant agent concentrations. A well-fitted empirical correlation represents the change in percentage oil removal with wide range of operating conditions was obtained. The oil separation reached 65% at optimum conditions; 75% in the presence of NaCl (3.5% by wt. of solution); and 92% with the presence of NaCl and at optimum concentration of flocculant agent. Electrical energy consumption varied from 0.5 to 10.6 KWh/m 3 according to experimental conditions. An equation relates the K with I was obtained. The general form of the equation is K = constant ( I) n ; where the n values are 0.6 4 and 0.62 for solutions with and without NaCl, respectively. The previous relation is valid only for current values from 0.3 to 1.2 A. The effect of emulsion flow rate on the separation process was determined on continuous scale.

The investigation of the advanced treatment of municipal wastewater by modular flotation-filtration systems and reuse for irrigation

The objective of this study was to provide clarified municipal wastewater effluent at the turbidity level of less than 2.0 NTU and reuse for landscape irrigation (golf course). For that purpose, during pilot -study first was used a combined flotation-filtration module-clarifier alone (Alternative I). A particularly designed configuration of the primary flotation unit and combined flotation-filtration clarifier, as a modular clarification system was used in the next step of the investigation (Alternative II). In addition, start up of the full scale plant was performed as well. In the first phase of this study, the impact of the type and concentration of coagulant and flocculant was tested. As a result, mechanisms of flocculation were proposed. Only under the moderate hydraulic loads (75.7-151.4 LPM)during pilot tests byAlternativel, was it possible to reach satisfactory turbidity reduction. By the Alternative II, the clarification performance was improved under the higher hydraulic load (302.8 LPM). The kinetics of the investigated flotation systems were assesed by empirical flotation models. Based on the pilot-study, Alternative II is recommended in order to reduce the high solids loadings under a higher hydraulic load, and it provided irrigation water at a required rate of 3785 m3/d during start up and optimization of the full scale plant.

Influence of flocculants on the performance of a ceramic capillary filter

Capillary filtration technology has been developed in Finland by Outokumpu Mintec Oy. Almost ten years of full scale experience of capillary filtration has shown that this type of filter is a very profitable and very economical solution to many filtration problems. The main area where capillary filters are used is in the dewatering of mineral concentrates. Both vacuum capillary as well as pressurised capillary filters are now commercially available. In the work reported here, the effect of flocculants on the capacity of Ceramec filters is studied. The titrations were made using three copper concentrates and a laboratory-scale automatic dipping machine. During the experiments no permanent plugging of ceramic filter media was observed. On the contrary, small concentrations of non-ionic or slightly anionic flocculants increased the capacity. However, too high a concentration of flocculants caused plugging of the ceramic plates. There were also remarkable differences between the copper concentrates used and their behaviour during filtration with Ceramec filters. Storage of copper concentrates changes their zeta potential very dramatically. In addition, the type of copper sample has an effect on the capacity. Clearly better capacities were achieved using a slurry sample which was brought straight from the mine, compared with using a copper sample which was first dewatered in a mining enrichment plant. The results show that these kinds of experiments should be performed in the mineral concentration plant if very accurate results are desired. A good way to predict the capacity and the cake moisture of mineral concentrates is to perform test filtrations using small, pilot-scale capillary action filters which can be directly connected to the mineral concentration process.

Estimation of the Hamaker constant from flocculation in the secondary minimum and its experimental verification in particle adhesion

The critical flocculation concentration, CFC, of a polystyrene latex (PSL) dispersion was determined from the change in transmittance after adding an electrolyte solution. The apparent values of the CFC obtained from transmittance vs. electrolyte concentration curves decreased with increasing stand time. From the CFC value obtained at the shortest stand time and the experimentally determined outer Helmholtz plane potential, the Hamaker constant between PSL particles in water was calculated by considering particle aggregation in the secondary minimum of the potential energy curve. The Hamaker constant was verified by adhesion experiments: the adhesion of PSL particles to a quartz plate was explained in terms of the total potential energies of interaction calculated from the obtained Hamaker constant on the basis of the heterocoagulation theory.

Chemical Conditions Conducive to the Release of Mobile Colloids from Ultisol Profiles

AbstractDispersed colloidal clay particles may enhance the transport of environmental contaminants adsorbed to the colloid surfaces. The objective of this study was to determine how soil pH (4.3–6.9), low total electrolyte concentration (TEC, 0.4–2.8 molc m‐3), and low Na adsorption ratios (SAR, 0.3–1.8 [molc m‐3]0.5) affected the concentration of mobile colloids released from 13.5‐m3 reconstructed Ultisol profiles. Critical flocculation concentration (CFC, the minimum TEC to induce flocculation of a clay suspension) tests were conducted using the water‐dispersible clay fraction of the Ap horizon of these profiles, which is the primary source for the mobile colloids. Surface soil pH, TEC, and SAR levels of the profiles that released high concentrations of colloids fell within the dispersion domain identified by the laboratory CFC tests. The effect of SAR on dispersion appears to be a continuum that approaches zero, and this effect is significantly (P ≤ 0.01) dependent on TEC. The dispersible nature of these soils is in part attributed to their very low TEC, generally <2 molc m‐3, which results from low concentrations of weatherable minerals. The TEC of 10 of the 13 profiles were <2 molc m‐3, the CFC for SAR = 1 (molc m‐3)0.5, indicating that if the pH is not limiting (pH greater than ≈6.0), colloidal dispersion will occur. Thus, these weathered soils can be highly dispersive within limited chemical conditions, and only small increases in SAR or pH may induce dispersion. By identifying these limits, the risk of enhancing subsurface contaminant transport by soil‐derived mobile colloids can be reduced.