Shear flocculation of celestite with sodium oleate and tallow amine acetate: effects of cations

Sodium oleate and tallow amine acetate (TAA) were used as surfactants for the shear flocculation of celestite. The shear-flocculation power values obtained with sodium oleate were higher than those obtained with TAA in terms of the concentrations used in the shear-flocculation experiments. In addition, sodium oleate and TAA were more effective on the celestite suspension in the pH ranges of 7-11 and 6-10, respectively. For the shear-flocculation experiments with sodium oleate at pH 11, with preaddition of calcium or magnesium ions at 5 x 10(-5) M and lower concentrations into the suspension, the shear flocculation of the celestite suspension was promoted by the coagulation process due to the calcium and magnesium cations added. However, the shear-flocculation power values decreased due to the interaction between surfactant and cations at concentration values higher than 5 x 10(-5) M for magnesium ions and 10(-3) M for calcium ion. Particularly, magnesium ions significantly reduced the shear-flocculation power values by slime coating of Mg(OH)2 precipitates.     

Effect of hydrolyzable metal cations on the coagulation between hexadecane and mineral particles

Mutual coagulation tests were conducted between hexadecane droplets (with and without doping with 0.001 mol/L sodium oleate) and micrometer-sized quartz, kaolinite, and illite particles in the presence and absence of multivalent hydrolyzable metal cations. It was observed that while hexadecane did not coagulate with quartz particles in the entire pH range tested (from 3 to 11), the presence of multivalent metal ions significantly increased the mutual coagulation between the hexadecane and quartz. And this only happened when the pH was raised to the level where first-order metal hydroxyl species and/or metal hydroxides were formed. The implications of this mutual coagulation for bitumen liberation from Alberta oil sands are discussed.     

Flocculated flow of microfibrillated cellulose water suspensions: an imaging approach for characterisation of rheological behaviour

Our aim was to characterise the suspension rheology of microfibrillated cellulose (MFC) in relation to flocculation of the cellulose fibrils. Measurements were carried out using a rotational rheometer and a transparent cylindrical measuring system that allows combining visual information to rheological parameters. The photographs were analyzed for their floc size distribution. Conclusions were drawn by comparing the photographs and data obtained from measurements. Variables selected for examination of MFC suspensions were degree of disintegration of fibres into microfibrils, the gap between the cylinders, sodium chloride concentration, and the effects of changing shear rate during the measurement. We studied changes in floc size under different conditions and during network structure decomposition. At rest, the suspension consisted of flocs sintered together into a network. With shearing, the network separated first into chain-like floc formations and, upon further shear rate increase, into individual spherical flocs. The size of these spherical flocs was inversely proportional to the shear rate. Investigations also confirmed that floc size depends on the geometry gap, and it affects the measured shear stress. Furthermore, suspension photographs revealed an increasing tendency to aggregation and wall depletion with sodium chloride concentration of 10⁻³ M and higher.     

Investigation of spherical oil agglomeration properties of celestite

In this study, concentration of celestite particles was investigated by using oil agglomeration. For this purpose, effects of operating parameters were investigated, and zeta potential measurements and Fourier transform infrared spectrophotometry (FTIR) analyses have also been carried out. In the experiments, effects of operating parameters such as pH, stirring speed, amount of Na oleate as a anionic type collector and kerosene as a bridging liquid, solid ratio, agglomeration time, collector stirring time, conditioning time, and amount of EDTA were investigated to obtain optimum conditions. Zeta potential measurements were carried out for various pH values and amounts of Na oleate. FTIR analyses were investigated to determine the adsorption type of Na oleate on celestite surface. By evaluation of the experimental results, optimum oil agglomeration conditions of celestite were determined as follows: pH 7, stirring speed 1500 rpm, amount of kerosene 100 l/t, amount of Na oleate 10 kg/t, solid ratio 5 wt%, conditioning time 5 min, collector stirring time 1 min, agglomeration time 5 min, and amount of EDTA 1.0 kg/t. In the optimum conditions, celestite was concentrated with recovery of 89.47 wt%.     

Hydrophobic Flocculation of Galena Fines in Aqueous Suspensions

The hydrophobic flocculation of galena fines induced by potassium amyl xanthate (PAX) in aqueous suspensions has been studied using laser diffraction, electrophoretic light scattering, contact angle, and microflotation measurements. The measurements were performed on <2 μm, 2-5 μm, 5-10 μm, and <30 μm size galena by varying several parameters, including PAX concentration, pH, original particle size, kerosene concentration, and suspension stirring. The experimental results have demonstrated that the hydrophobic flocculation was closely correlated with the particle hydrophobicity, but was not lowered upon increasing the particle surface charges due to PAX adsorption, which is contrary to the DLVO theory. This flocculation has been observed to increase with a reduction of the original particle size and an increase in kerosene concentration, and to require sufficient stirring strength and magnitudes of kinetic energy input to achieve the maximum aggregation degree. From the microflotation results, it has been found that the flotation response of galena fines is markedly improved due to the formation of hydrophobic flocs, suggesting that floc flotation is a promising means to recover galena in the fine size range. Copyright 2000 Academic Press.     

Effect of floc structure on the rate of shear coagulation

We derived a mathematical expression for the temporal evolution of the number of particles due to shear coagulation, covering the later stage by expanding the initial stage approximation to take into account the formation of floc structure. In the derivation, it is assumed that flocculation proceeds through binary collisions between identical fractal flocs. The capture efficiency between flocs is calculated on the basis of trajectory analysis, which is determined by viscous hydrodynamic interaction between flocs and van der Waals attractive forces between two primary particles located at colliding points of flocs. The validity of the derived equation was tested by a coagulation experiment using polystyrene sulfate latex particles under conditions of rapid coagulation. The experiment was carried out in a laminar Couette flow generated in the gap between two concentric cylinders. Careful and direct observation of flocculation under microscopy provided the data on the fractal dimension as well as the temporal evolution of number concentration of flocs. The measured rate of coagulation gradually increases in accordance with the formation of the fractal structure of flocs. This behavior agreed very well with the prediction based on the derived equation.     

Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.     

Quantitative determination of inorganic minor cations in sodium-, calcium-, magnesium-matrix simulated samples by capillary electrophoresis

The analysis of ammonium, alkali and alkaline-earth trace cations (0.5 ppm) in samples with a calcium, sodium or magnesium matrix (500 ppm) has been achieved using 10 mM imidazole (pH 4.5) electrolyte to which a complexing agent (15-crown-5, oxalic acid or dipicolinic acid) has been specifically added in order to decrease the electrophoretic mobility of the matrix cation and thus to allow the separation of higher mobility cations at sub-ppm concentrations. The influence of several experimental parameters (complexing agent concentration, buffer pH and temperature) have been studied in order to optimize the separation. The complexing agent concentration appears to be the main parameter governing the selectivity of the cations during the analysis of matrix samples. In optimized conditions, we have checked that the separation between minor inorganic cations is not significantly altered by an increase in the matrix cation concentration. As the concentration of the matrix cation increases, the migration times of minor cations remain unchanged even for a 1000 ppm concentration of the matrix cation. Finally, these optimized buffers allow the quantitation of minor cations down to 0.05% (w/w) for calcium- or magnesium- matrix simulated samples and 0.2% (w/w) for sodium-matrix simulated samples.     

Quantitative capillary electrophoretic analysis for calcium and magnesium in sodium–matrix waters

A method was developed for the quantitative analysis for calcium and magnesium in sodium–matrix waters using capillary electrophoresis with indirect detection. Separation of the divalent metals from the matrix ion was investigated via addition of a weak diacid in the electrolyte. The optimum separation conditions were chosen after simulations of the migration times of the cations at pH 5.0 and were experimentally tested. Among the selected diacids, oxalic acid and tartaric acid gave the best peak-to-peak resolution for all the cations. The cationic chromophore was selected from a series of weak bases. Optimisation of the sensitivity for the alkaline–earth metals was investigated via alteration of the electrolyte pH to adjust the mobility of the chromophore to those of the cations. The best analytical conditions were obtained with 10 mM creatinine/2mM oxalic acid, pH=4.6 and 14.4 mM benzylamine/8 mM tartaric acid, pH=4.8. System peaks were sometimes present in the potassium and sodium regions but did not interfere with the quantitative treatment. Limits of detection of 4 μM were achieved in a simulated matrix containing 500 ppm of sodium, whcih corresponds to the upper limit for the matrix–ion concentration. The proposed method was applied to the determination of calcium and magnesium ions in saline underground waters.     

Calcium and magnesium cations enhance the adhesion of motile and nonmotile pseudomonas aeruginosa on alginate films

We investigated the impact of calcium and magnesium ions on the deposition kinetics of flagellated and nonflagellated Pseudomonas aeruginosa onto an alginate conditioning film in a radial stagnation point flow system. The bacterial deposition/adhesion behavior was related to structural changes of the alginate film in the presence of the divalent cations. Our results showed that adhesion of nonmotile bacteria was governed by cation bridging interactions between high-affinity sites at the bacterial surface and either clean or alginate-conditioned substrate surfaces. For motile bacteria, the adhesion onto clean quartz was governed by electrostatic interactions while adhesion onto alginate-conditioned quartz was dependent on the structure and viscoelastic properties of the alginate film in the presence of calcium or magnesium. We demonstrate that bacterial adhesion behavior is governed both by the effects of divalent cations on the surface properties of the bacteria and the substrate and by the type of specific interactions occurring between these two surfaces.     

Adsorption of guar gum onto quartz from dilute mixed electrolyte solutions

The effect of potassium, sodium, calcium, magnesium, and hydrogen cations on adsorption of guar gum onto quartz was investigated at natural pH. The role of the background ions was analyzed in terms of their water-structure making or breaking capabilities. In dilute solutions (0.01 mol/L) of structure-makers (NaCl, HCl, CaCl2, and MgCl2), the guar gum adsorption density did not change compared to the adsorption densities obtained in distilled water. Potassium, the only structure-breaking ion (chaotrope) among the tested cations, significantly enhanced guar gum adsorption. The results obtained in mixed electrolytes demonstrate that the strong structure-breaking properties of K+ overcome any contributions from weak structure making ions (kosmotropes), and guar gum adsorption remains at the levels observed in KCl alone. Only when strongly hydrated Mg2+ ions are mixed with KCl, the overall effect becomes additive and the influence of potassium is proportionally reduced by increasing concentrations of magnesium cations. In this approach, guar gum adsorption on quartz is viewed as a competition between polysaccharide and water molecules for silanol surface sites. The hydration of the quartz surface inhibits the adsorption process but the competition equilibrium, and hence polysaccharide adsorption, can be affected by the presence of chaotropes or kosmotropes.     

Incorporation of blood clotting factor X into phospholipid model membranes: fluorescence microscopy imaging and subphase effects surrounding the lipid phase transition region

Factor X is a blood clotting protein that associates at membrane surfaces to become activated during the coagulation cascade. A molecular level understanding of the protein-membrane phospholipid interactions has not been reached, although it is thought that the protein binds to phospholipids in the presence of calcium through a bridge with the Gla (gamma-carboxyglutamic acid) domain on the protein. In this work, phospholipid Langmuir monolayers have been utilized as model membranes to study factor X association with phospholipid membrane components. Surface pressure measurements indicate that subphase addition of sodium, magnesium, and calcium ions enhances protein penetration of the lipid monolayer, with the largest association found with calcium ions in the subphase. Fluorescence microscopy images collected after protein penetration of lipid monolayers indicate monolayer condensation in the presence of sodium and magnesium ions. Aggregation of lipid domains is induced when calcium is in the subphase, indicating binding-induced flocculation of surface lipid aggregates. Calcium binding to factor X likely causes a conformational change which allows protein-membrane interaction via hydrophobic association with lipid molecules.     

Determination of electrochemical kinetic parameters by square-wave polarography: Polarographic reduction of Zn(II) in concentrated nitrate and perchlorate supporting electrolyte solutions

The electrochemical kinetic parameters for the polarographic reduction of Zn(II) at a dropping mercury electrode in concentrated supporting electrolytes consisting of sodium, ammonium, lithium, magnesium and calcium nitrates and sodium perchlorate have been determined at 25.0±0.1°C by the square-wave polarographic method. The rate parameter decreased with increase of radius of the alkali-metal cations present in the electrolyte and with increase of charge of the cation of the electrolyte in solution of the same ionic strength. It also decreases, passes through a minimum and then increases with the increase in the concentration of any of the supporting electrolytes. The initial decrease is ascribed to the Frumkin double-layer effect but the latter increase has been explained in terms of the change in the activity of water around the electrode.     

Determination of the critical surface tension of wetting of minerals treated with surfactants by shear flocculation approach

This paper contributes the shear flocculation method as a new approach to determine the critical surface tension of wetting of minerals treated with surfactants. This newly developed approach is based on the decrease of the shear flocculation of the mineral suspension, with decreasing of the surface tension of the liquids used. The solution surface tension value at which shear flocculation does not occur can be defined as the critical surface tension of wetting (gamma c) of the mineral. By using the shear flocculation method, the critical surface tensions of wetting (gamma c) for calcite and barite minerals, treated with surfactants, were obtained as 30.9 and 35.0 mN/m, respectively. These values are in good agreement with data reported previously on the same minerals obtained by the contact angle measurement and flotation methods. The chemical agents used for the treatment of calcite and barite particles were sodium oleate and sodium dodecyl sulfate, respectively.     

Determination of fluoride ions in urinary stones by ion chromatography

A method of the ion chromatographic determination of fluoride ions in urinary stones has been developed. Sample preparation of solid mineral-organic samples includes dissolution in concentrated hydrochloric acid, dilution with deionized water, and the elimination of excess calcium and magnesium cations by adding a KU-2 sulfo cation exchanger in the H-form to samples and filtration through a membrane filter. Anions were separated on a Shim-pack IC-AIS anion-exchange column (100 × 4.6 mm) with elution with a mixture of 2.0 mM phthalic acid and 1.2 mM sodium hydroxide (pH 3.5). The linearity range of the fluoride ions in the obtained solutions of urinary stones with conductometric detection was 0.01–300 mg/L, the limit of detection calculated by the 3s-test was 0.004 mg/L. The quantitative determination of fluoride ions in 20 samples of urinary stones was performed; in 80% of cases the presence of fluorides in the stones at a level from 0.01 to 4 mg/g of the stone was detected. The average concentration of the fluoride ions was 0.3 mg/g of stone. For 20% of the samples an elevated concentration of fluoride ions compared to the average one was found.     

THE EFFECT OF DISPERSANT REAGENTS ON THE SODIUM OLEATE ADSORPTION AT THE SALT MINERALS-WATER INTERFACE

The influence of some dispersant reagents on the sodium oleate adsorption on the salt minerals surface has been investigated at the vicinity of pH 10. The presence of sodium lignin sulfate and low molecular weight acrylic polymer Cataflot P-40 caused the decrease of surfactant adsorption in the low concentration region of sodium oleate. On the other hand, the addition of 1000 g/t of polyethylene oxide (MW 200 000) did not cause such a change. The special shape of the adsorption isotherms has been done by the bidimensional concentration of alkaline earth metals soaps on the carbonate minerals surfaces. The vertical steps of isotherms were shifted to the high sodium oleate concentration region when both sodium lignin sulfate and Cataflot P-40 were added to the dolomite and magnesite suspensions. This effect was not observed for the calcite-sodium oleate system. The discrepancy was explained by Die blockade of magnesite species by these dispersant reagents. Changes in electrokinetic and stability behavior of these systems have been correlated with the precipitation conditions of both calcium and magnesium oleate.     

Effect of temperature and pH on droplet aggregation and phase separation characteristics of flocs formed in oil–water emulsions after coagulation

Coagulation process is used for destabilization of emulsions to promote aggregation of oil droplets on flocs which can be subsequently removed by sedimentation or flotation. The objectives of this study were to investigate the effect of temperature and pH on the effectiveness of destabilization of olive oil–water emulsions in relation to floc morphology and aggregation characteristics of oil droplets, and to quantify the ability of flocs to capture and separate oil. A cationic polyelectrolyte was used for the coagulation of oil droplets in edible olive oil–water emulsions using a jar test apparatus. The flocs formed in olive oil–water emulsions after coagulant addition were analyzed using microscopic image analysis techniques. Fractal dimension, radius of captured oil droplets on flocs, number of oil droplets aggregated on flocs, and floc size were used to quantitatively characterize and compared the effectiveness of the coagulation process at different conditions (pH and temperature) and the ability of flocs to remove oil from water. Analysis of microscopic images showed that floc size was not always the best measure of effectiveness of coagulation process in oil–water emulsions. The flocs forming at different pH levels and temperatures had significant morphological differences in their ability to aggregate different sizes and numbers of oil droplets, resulting in significant differences in their ability for separating oil. Fractal dimension did not correlate with the ability of flocs to aggregate oil droplets nor the total amount of oil captured on flocs. Temperature had a significant effect on droplet size and number of droplets captured on flocs. The differences in floc sizes at different temperatures were not significant. However, the flocs forming at 20 °C had fewer but larger droplets aggregating larger amounts of oil than flocs formed at 30 °C and 40 °C. The size of droplets at different pH levels was similar, however, there were significant differences in number of droplets aggregating on flocs and floc sizes. The amount of oil captured on flocs at pH 7 and pH 9 was significantly higher than those at pH 5 and pH 11. The calculated fractal dimensions of the flocs (all less than 1.8) indicated that the coagulation process was diffusion limited implying that there was no repulsion between the colliding particles (i.e., droplets and flocs); hence, each collision between flocs and droplets resulted in attachment.     

The behaviour of micro-bitumen drops in aqueous clay environments

This study summarises the rheological behaviour of emulsion bitumen drops in the presence of aqueous solutions of de-ionised or process water (DIW or PW) containing montmorillonite clays (M) and/or calcium ions (Ca++). The presence of calcium ions and montmorillonite clays resulted in the plastic behaviour of bitumen drops. In a DIW+M+Ca++ system, increasing temperature and calcium ion concentration resulted in an increase in the number and degree of plastic bitumen drops. In the presence of considerable amounts of Ca++ ions and/or at higher experimental temperature, bitumen drops in a PW+M system exhibited no significant overall plasticity of their surfaces. Both calcium and sodium ions contained in process water compete with each other to occupy the montmorillonite clay surface. At the pH value of process water (pH congruent with8), increasing the temperature did not change the value of bitumen droplet zeta potential. Stability of bitumen-in-water emulsions at 22 degrees C showed that bitumen droplets coalesced upon contact in the DIW+M system. The addition of calcium ions (Ca++) led to the inhibition of coagulation and coalescence of bitumen droplets, which may indicate the formation of CaM aggregates at the bitumen-water interface.     

Preconcentration and determination of calcium and magnesium in brine with flow-injection systems

On-line preconcentration on a chelating resin (Dowex A-1) and elution with 0.1 M hydorchloric acid is followed by spectrophotometry based on the metal complexes formed with 1- (2-hydroxy-4-diethylamino-1-phenylazo)-2-hydroxynaphthalene-3,6-disulfonic acid. The total concentration of calcium and magnesium is determined; in a second sample, calcium is masked with a ligand buffer containing excess of barium(II) and EGTA, and magnesium is determined. The calcium concentration is measured by difference. Magnesium (1–30 μg l^?1 and calcium (8– 10 μg l^?1) in 2.5 M sodium chloride can be determined. Calcium and magnesium in analytical reagent-grade sodium chloride and potassium chloride and primary standard sodium chloride are aslo determined. The method based on the exchange between calcium ions and Mg(EDTA) is proposed to enchance the sensitivity for calcium.     

Quantification of anions and cations in environmental water samples. Measurements with capillary electrophoresis and indirect-UV detection.

The aim of this study was to validate two separation methods for determination of inorganic anions and cations from natural waters with capillary electrophoresis (CE) by using indirect-UV detection. The research is related to method development for screening of groundwater samples obtained in site investigations for spent fuel of the Finnish nuclear industry. In CE analysis, anions were separated in pyromellitic acid (pH 7.7) in the order bromide, chloride, sulphate, nitrite, nitrate, fluoride and dihydrogenphosphate. Cations were separated at pH 3.6 after anions using an 18-crown-6-ether solution. In these analyses, ammonium migrated first followed by potassium, calcium, sodium and magnesium. The concentrations of the ions in the natural water samples were calculated by using two or three calibration curves made using reference solutions at concentration levels of 0.5-250 mg/l. The repeatabilities of the anion and cation methods were tested using laboratory-made reference sample mixtures with high and low salt concentrations. The limits of quantification in the analyses were between 0.02 and 0.1 mg/l, depending on the ion. Concentrations of ions tested in natural waters varied from a few milligrams to tens of grams per litre.