Calcium Carbonate Suspensions Research Articles

The Influence of Stabilizing Agents on the Interaction between Styrene/Butadiene Latex and Calcium Carbonate: A Calorimetric and a Dynamic Electrokinetic Study

The role of stabilizing agents in the interaction between styrene/butadiene latex and calcium carbonate particles has been studied using isothermal titration calorimetry (ITC) and an electrokinetic sonic amplitude (ESA) technique. It is demonstrated that the polyacrylate sodium salt (dispersing agent, referred to as NaPA) used as stabilizing agent for the calcium carbonate suspensions principally affects the interfacial properties of the calcite surface. An electrostatic barrier is created and this decreases the attractive interactions between the latex and the negatively charged mineral surface. The total enthalpy change observed when an emulsion of styrene/butadiene particles substantially free from surfactant was added to the dispersed calcium carbonate could be described via a relatively complex path. The process included (i) an exothermic response from the association of the latex particles (adsorption process) with the dispersed calcium carbonate surface and (ii) an endothermic bulk phase effect due to the adsorption on the latex particles of dissolved species originating from the calcium carbonate. Stabilization of the latex particles with sodium dodecyl benzene sulfonate (SDBS) or a non-ionic fatty alcohol ethoxylate surfactant did not significantly change the enthalpy of interaction. It was further demonstrated that SDBS had a very weak affinity for the dispersed calcium carbonate particles and that dissolution of species, such as calcium ions, from the calcium carbonate surface, allows further adsorption of SDBS onto the latex particles.

Aspects on the Interaction between Sodium Carboxymethylcellulose and Calcium Carbonate and the Relationship to Specific Site Adsorption

The mechanisms of adsorption and association for sodium carboxymethylcellulose (NaCMC) in calcium carbonate suspensions have been determined from isothermal calorimetry and adsorption measurements. The equilibrium adsorption isotherms were determined by two different methods of separation; a depletion method and a serum exchange method. The enthalpy of dilution for NaCMC was determined on supernatants obtained from the calcium carbonate suspensions in order to investigate the interaction between NaCMC and dissolved species from the mineral. For comparison, NaCMC was injected into CaCl2 solutions in order to determine the role of calcium ions in the adsorption process. The initial part of the adsorption isotherm showed a quasi-infinite slope indicating a high affinity for the NaCMC to the calcium carbonate surface, which was significantly reduced when anionic sodium polyacrylate was preadsorbed onto the calcium carbonate implying competitive adsorption. An endothermic enthalpy change was observed between the NaCMC and the calcium carbonate surface, suggesting attachment of the carboxylic acid groups onto the hydrated calcium sites. A similar endothermic enthalpy was observed when NaCMC was injected into CaCl2 solutions or supernatants obtained from the calcium carbonate suspensions, indicating a complexation of carboxylic acid groups and hydrated calcium ions. It was concluded that the mechanisms of interaction of NaCMC in calcium carbonate suspensions are primarily an association between NaCMC and Lewis acid sites on the calcium carbonate surface and the formation of NaCMC–Ca2+ complexes in the bulk solution, both of which will be affected by the amount of anionic sodium polyacrylate present.

Effects of organic matrix proteins on the interfacial structure at the bone–biocompatible nacre interface in vitro

The biocompatibility and potential osteoinductivity of nacre have favored its use as a bone-grafting material. The present study is to investigate the interfacial structure at the bone–nacre interface resulting from organic matrix proteins, which emphasizes the mechanism of bone-bonding ability and biocompatibility of the shell tissues such as nacre and biogenic calcite. To understand the interfacial reaction, the zeta potential measurements, provide for a unique method to quantify the actual state of the interface in situ, were used for synthetic and biogenic calcium carbonate suspensions with respect to pH and the organic matrix as an additive. The zeta potentials and surface charge density show that the organic matrix proteins are main charge regulators, resulting in the stabilized tissue properties as compared with synthetic crystals. Also, in forming calcium carbonate crystals with the additives, the conformation of organic matrix has an important role in the understanding of the newly formed interfacial structure. The result provides the primary role of the organic matrix proteins in controlling the formation of interfacial structure and biocompatibility with bone as well as the stability of biogenic tissues. And it gives a new insight into the usefulness of zeta potential measurement to describe the in vivo interaction between the bone and implants.

Hydrodynamic parameters from the Michaels and Bolger method

For different initial heights and solids concentration of flocculated calcium carbonate suspensions in the compression range, the variations of the subsidence rates are discussed in accordance with the Michaels and Bolger method. A mathematical model based on the consolidation theory has been applied to generalize the Michaels and Bolger method, and to discuss the relationships between the permeability, the effective pressure and the solids concentration. In accordance with this model and the experimental results, it is deduced that the relationship between the effective pressure and the solids concentration differs considerably from that obtained by other methods, whereas the values of permeability for different solids concentration are close to those deduced by different methods.

The Dispersion Properties of Precipitated Calcium Carbonate Suspensions Adsorbed with Alkyl Polyglycoside in Aqueous Medium

The zeta potentials and dispersion properties of precipitated calcium carbonate suspensions adsorbed with alkyl polyglycosides in aqueous medium were investigated. Within the investigated pH ranges, the adsorption curves of alkyl polyglycosides on calcium carbonates show sigmoidal shapes, and the zeta potential decreases as the amount of adsorption increases. At positively charged surfaces of low pH, the adsorption amounts were greater than those at negatively charged surfaces, indicating that alkyl polyglycosides were negatively charged in aqueous solutions. At low concentrations of alkyl polyglycosides, the dispersion stabilities of suspensions were very poor and showed no linearity with zeta potentials over the entire range of pHs, which may be attributed to the onset of hydrophobic interaction between particles due to the adsorption of surfactant molecules. This destabilization continued until monolayer coverage by the surfactant layer was complete. Based on the classical DLVO theory, there may be a strong hydrophobic interaction between particles. Beyond monolayer adsorption, the dispersion stability increases, probably by the formation of hemimicelle or admicelle. Therefore, it is believed that ionization of alkyl polyglycosides and admicelles of surfactants on particle surface plays a key role in the stability of dispersions and the abrupt increase in adsorption.

Settling in aggregating colloidal suspension: Analysis of cell inclination influence

We present the study of the settling of a colloidal gel in a cell tilted at an angle . In suspensions of non-colloidal particles, the inclination of the sedimentation cell leads to a large enhancement of the settling velocity known as “Boycott effect” well described by the PNK model. We show that the specific mechanical properties of a colloidal gel can give way to kinetics of settling very different from usual suspensions which can no longer be described using a simple PNK model. In particular, we study the influence of the very voluminous sediment generally formed in such systems. We thus propose a complete description of the kinetics of a settling colloidal gel according to its volume fraction and to the cell inclination angle. In the experimental section, the predicted settling regimes are compared to experimental results obtained with calcium carbonate suspensions. The agreement between theoretical expressions and experiments is good which shows that our results are relevant to most experimental studies of tenuous colloidal gels.

Influence of geometry and angular velocity on performance of a rotating disk filter

AbstractThe influence of internal geometry and angular velocity on the performance of a rotating‐disk filtration device is described. This module consists of a disk rotating at speeds up to 2,000 rpm inside a cylindrical housing equipped with a fixed flat membrane. The test fluid was a calcium carbonate suspension (4.7‐μm mean particle diameter), and the membranes were in nylon (0.2‐μm mean pore diameter) and PVDF (0.1 and 0.18 μm). The shear stress on the stationary membrane in the laminar boundary‐layer regime was estimated from a similarity solution, and in the turbulent regime from the friction coefficient for a flat plate. Several inlet and outlet configurations were tested. The permeate flux was independent of the axial gap (disk to membrane), but increased when the radial gap (from disk to housing) was raised from 2 to 5 mm. The inviscid fluid core in the axial gap was observed to rotate at 42% of angular velocity with a smooth disk. This factor rose to 64% when the disk was equipped with small vanes. Fouling was limited to the central part of the membrane at 1,500 rpm and disappeared completely for a disk equipped with vanes. Permeate fluxes were consistently much higher than in classic cross‐flow filtration.

Filtration with Sedimentation: Application of Kynchs Theorems

Filtration at moderate rates on upward-facing horizontal surfaces is accompanied by sedimentation. Kynch theorems developed for sedimentation in the noncompression range can be adapted to explaine the evolution of the cake surface and the filtrate volume with time. The different relationships obtained have been tested with filtration + sedimentation runs and filtration without sedimentation runs carried out with calcium carbonate suspensions at moderate pressure differences from 17 to 97 mmHg. The differences between the average specific resistance observed at the different runs can be satisfactorily explained by the fundamentals of the theory.

CHARACTERISATION OF CAKE COMPRESSIBILITY IN DEAD-END MICROFILTRATION OF MICROBIAL SUSPENSIONS

Culture broths of Saccharomyces cerevisiae and Kluyveromyces marxianus var marxianus NRRLy2415, suspensions of rehydrated active dry bakers yeast and suspensions or calcium carbonate were filtered in dead-end mode at pressures below 200 kPa. In the case of all the microbial suspensions, the specific cake resistance was found to be a linear function of pressure. Cake compression was found to be reversible or weakly irreversible with respect to changes in pressure, i.e., the specific resistance measured at a given pressure was only weakly dependent on whether the filter cake had previously been exposed to higher pressures. The greatest irreversibility effects were obtained with unwashed active dry yeast suspensions, consistent with the breakdown of cell aggregates in these suspensions. The specific cake resistance of calcium carbonate suspensions was found to be a non-linear function of pressure. The compression of calcium carbonate cakes was irreversible, consistent with the breakdown of the large number of particle aggregates in these suspensions.

Colloidal processing of calcium carbonate

Two natural calcium carbonate (CaCO 3) powders were dispersed in aqueous media and their colloidal processing ability was studied. In absence of dispersant, electrophoretic measurement showed a very low surface charge density on calcium carbonate particles that do not allow the preparation of stable suspensions suitable for the casting process. However, the addition of an appropriate dispersant caused a significant increase of the surface charge density of CaCO 3 powders, enabling the preparation of relatively dense suspensions. Calcium carbonate suspensions with very high solid loading (60 vol%) and viscosities low enough for casting operations could be prepared. Rheological measurements and casting experiments were performed in order to correlate the flow characteristics of the slips with the particle ability towards packing. Very high green and sintered densities were obtained, reaching more than 74 and 95% of the theoretical density, respectively. Considering the availability, low price and the processing ability of calcium carbonate by colloidal techniques, as revealed in this work, this material can represent a useful option for ceramic manufacture.

Scaling analysis of sediment equilibrium in aggregated colloidal suspensions

The equilibrium of aggregated colloidal suspensions under gravity is studied both theoretically and experimentally. Using a simplified model to describe the compaction of the gelled suspension, we show that the volume fraction of the particles needed to form a stable gel is not intrinsic to the physicochemical system but depends on the height of the sample, its aspect ratio, and the friction between the suspension and the cell wall. A scaling analysis is developed to predict the various regimes encountered and to calculate the variations of the equilibrium sediment height as a function of the volume fraction of the particles and the height, and width of the sample. Good agreement is found with systematic measurements performed on aqueous colloidal calcium carbonate suspensions.

Dispersion, Stabilisation and Casting of Calcium Carbonate Suspensions

Dispersion, Stabilisation and Casting of Calcium Carbonate Suspensions

Sedimentation and Compaction of Calcium Carbonate Aggregating Suspensions : Scaling Analysis of the Equilibrium

Aggregating suspensions generally separate into a clear supernatant and a voluminous gelled sediment. The suspension remains homogeneous (i. e. a gel stable under gravity forms) only when the volume fraction of particles exceeds a given value Phi**. The present study is devoted to the determination of Phi**. A simplified model describing the gel equilibrium has been developed and its validity is checked comparing its predictions to systematic measurements of the sediment volume performed on calcium carbonate suspensions. Applying this model to the prediction of Phi**, we show that Phi** is not a characteristic of the physico-chemical system but depends on the height of the sample, its aspect ratio and friction between the gel and the side wall. For large (respectively small) aspect ratios, we find that Phi** is a power law function of the width (respectively the height) of the sample involving an exponent 1/(K - 1) which is related to the dependence of the yield stress on the volume fraction of the suspension.

Changes in zeta potential of TiO2 and CaCO3 suspensions treated with a radiofrequency electric field as measured with a ZetaPlus instrument

Abstract Zeta potentials for titanium dioxide (Degussa, P 25) and calcium carbonate (Fluka; more than 99.0% pure) suspensions prepared in water or 0.01 M NaCl at different pH were measured after exposure to a radiofrequency (44 MHz) electric field for 5–30 min. The measurements were performed using a fully automatic ZetaPlus instrument which allowed the determination of the zeta potential at an exact time after the removal of the field, i.e. 5 or 10 min. These studies were performed in order to verify the previous results which were obtained by the classical microelectro-phoretic method. It has again been proved that the field affects the zeta potential of the systems, it is believed by absorption of field energy which is then dissipated. Both the adsorption and the dissipation of the energy seems to occur in an oscillatory manner, as is reflected in time-dependent changes of the zeta potential. The observed zeta potential changes are probably due to a shifted adsorption-desorption equilibrium of the potential-determining ions.

Changes in zeta potential and surface free energy of calcium carbonate due to exposure to radiofrequency electric field

A calcium carbonate (Fluka; more than 99.0% pure) suspension or a thin layer of its powder deposited on a glass slide was exposed to an r.f. electric field (44 MHz; 60 V peak-to-peak no-load amplitude) for 5–30 min. The zeta potential of the suspension in water (natural pH, 9.9 ± 0.1) or in 10 −2 M NaCl (natural pH, 9.6 ± 0.1) was then measured electrophoretically. The surface free energy components, i.e. non-polar Lifshitz—van der Waals (γ LW S) and polar (acid—base) electron donor (γ − S) and electron acceptor (γ + S) were determined by the “thin-layer wicking technique”. It was found that a negative zeta potential of CaCO 3 in water measured immediately (within 2–3 min) after the exposure to the r.f field changed in an oscillatory fashion depending on the exposure time. For the sample treated for 15 min with the r.f field the zeta potential decreased by 5–7 m V in relation to an untreated sample. Residual changes occurred also in an oscillatory fashion during the 40 min after field removal. A similar behavior was found for the suspension in 10 −2 M NaCl. The observed zeta potential changes were accompanied by changes in the electron donor component of the surface free energy and the appearance of a small electron acceptor component, which resulted from the presence of hydrogen bonding on the calcium carbonate surface. The r.f. field treatment led to a decrease in γ − S from 83 mJ m −2 (untreated sample) to 40 mJ m −2 (15-min-treated sample) and 64 mJ m −2 (25-min-treated sample) and caused the appearance of γ + S components of 1.34 and 1.77 mJ m −2. The observed changes in the zeta potential and the surface free energy components are believed to result from the changes in the surface charge of calcium carbonate and the structure of the water film at the surface.

Management of scale deposits by diamagnetism. A working hypothesis

Abstract The basis for diamagnetism eliminating calcium carbonate deposits has been considered, and hypotheses include structure‐forming forces, reduced mechanical strength of scale formed, effects on crystal size, and rates of nucleation. Another hypothesis, advanced here, is that a magnetic field of suitable strength imposes a Zeeman effect on a diamagnetic substance, and there is a concomitant increase in entropy (an increase in the number of available “boxes"). The hypothesis was tested first with saturated aqueous magnesium hydroxide, and then with aqueous suspensions of calcium carbonate. The variation of pH in the presence and absence of a magnetic field followed the pattern predicted from the hypothesis: in the presence of a magnetic field for either system, the pH increased to a maximum value that remained constant. Removal of the magnetic field was accompanied by a slow (ca 17 hours) decrease in pH with time until the initial equilibrium pH was attained. Effects of carbon dioxide were minimized by using boiled deionized water and maintaining a nitrogen atmosphere during the experiments. Implications of the hypothesis and the tests are considered.

Colloidal suspensions of calcium carbonate in soils and their likely significance in the formation of calcic horizons

Evidence is presented to demonstrate that colloidal suspensions of calcium carbonate can be produced in the laboratory from naturally occurring CaCO 3 (Upper Chalk) and from a range of calcic horizons (Typic Hapludalf, southern England; Calcixerollic Xerochrept, southern Iran; and Xerollic Calciorthid, lower Egypt). Calcium carbonate in these calcic horizons and associated k-fabrics is in the form of colloidal-sized platelets. Particle size and ability to remain in colloidal suspension were determined for unground and for “TEMA” ground samples. Particle composition was determined using X-ray diffraction, differential thermal analysis and from X-ray fluorescence spectra (XRF). Particle morphology was obtained using the scanning electron microscope (SEM). The spatial morphological patterns observed in the calcic horizons of the three soils consisted of silt-sized, calcite platelets linked together by discontinuous coatings of both single and aggregated clay-sized, calcite platelets. Thus, as calcium carbonate in the soils was shown to be in colloidal form, the spatial and morphological patterns observed at the submicroscopic scale are attributed to physical transport of colloidal complexes rich in calcium carbonate. On mobilization, these colloidal complexes will be transported through inter-, intra- and transpedal pores by movement of soil water and deposited on ped surfaces and as linings to pore walls. Transport of colloidal calcium carbonate and deposition from suspension onto ped and pore surfaces is considered to be enhanced by irrigation practices and by lateral throughflow of water, that is by periodic and discrete soil/water/gravity events.

Pressure effects on the shearing of a colloidal thin film

The pressure effect in the frictional behaviour of a colloidal suspension of over-based calcium carbonate stabilized in pure dodecane has been investigated. With a surface force apparatus, the authors have observed the squeeze effect and the frictional resistance of the suspension using sphere- and plane-geometry on a nanometric scale and for low contact pressure (104 to 106 Pa). With tribometers, which can support heavy loading, they have analysed the high pressure domain (104 to 109 Pa). After a critical pressure, evaluated at 106 Pa, the colloidal film does not flow in the contact of the solids, but forms a compacted 'mattress' sliding on the plane surface, and squeezing a hydrocarbon layer. The mean shear strength of the interface, tau , can then be expressed by a relation of the form tau = tau 0+ alpha p, where p is the mean contact pressure. The meaning of tau 0 and alpha is discussed.

A Comparison of the Coefficients in the Richardson and Zaki's and Steinour's Equations Relating to the Behavior of Concentrated Suspensions

Abstract Steinour and Richardson and Zaki proposed relationships to explain the hindered settling phenomena from their independent experiments about 10 years apart. An attempt has been made to compare the coefficients and derive a relationship between Steinour's parameter A and Richardson and Zaki's parameter n. It is possible to express this relationship in the form of an equation involving parameters for which values can be assigned. Theoretically, this derived relationship should be applicable to any sedimenting suspension which obeys both Steinour's and Richardson and Zaki's equations. This derived expression has been evaluated for various experimentally determined values of A and n. The experimental systems which have been tested include calcium carbonate suspensions in water, sucrose-water, and glycerin-water solutions, and ethyl alcohol and magnesium hydroxide suspensions in glycerin-water, sucrose-water and sorbitol-water solutions. The calculated values have been shown to agree well with experime...

Interpretation of the Hindered Settling of Calcium Carbonate Suspensions in Terms of Permeability

Many pharmaceutical formulations are produced in the form of concentrated suspensions. Calcium carbonate suspensions are used in this study and interpreted as the “model” for the behavior of such suspensions. The behavior of concentrated suspensions of powders in a liquid medium cannot be treated by the simple application of the normal principles of free fall and the use of Stokes Law pertaining to the viscous resistance offered by the surrounding fluid to fall. A single particle operating by the Stokes principle obeys this relationship. This law applies to the behavior of particles at low concentration in a liquid medium and is the basis for particle size distribution methods. At higher concentrations, however, the particles do not enjoy the freedom of unhindered fall. The system subsides “en bloc” and it is common practice to offer a modification to the Stokes equation which takes into consideration some function of the porosity of the system. There have been a considerable number of equations developed and modified based on this principle. However, an alternative method is to approach the problem by dealing with the permeability of a bed of powders in a liquid in which the bed is slowly altering with time. This is best achieved by the use of the permeability equation developed and presented by Kozeny–Carmen. This equation, as well as the Richardson–Zaki expression, are related to show that the Kozeny parameter K varies with the suspension porosity under sedimentation conditions. The values of K are often larger than the value normally reported (i.e., ~5). The data and treatment outlined here are extended to include not only the calcium carbonate suspensions, but other systems previously mentioned in the literature.