Dilute Clay Suspensions Research Articles

Low frequency complex dielectric (conductivity) response of dilute clay suspensions: Modeling and experiments

In this work, we establish an effective medium model to describe the low-frequency complex dielectric (conductivity) dispersion of dilute clay suspensions. We use previously obtained low-frequency polarization coefficients for a charged oblate spheroidal particle immersed in an electrolyte as the building block for the Maxwell Garnett mixing formula to model the dilute clay suspension. The complex conductivity phase dispersion exhibits a near-resonance peak when the clay grains have a narrow size distribution. The peak frequency is associated with the size distribution as well as the shape of clay grains and is often referred to as the characteristic frequency. In contrast, if the size of the clay grains has a broad distribution, the phase peak is broadened and can disappear into the background of the canonical phase response of the brine. To benchmark our model, the low-frequency dispersion of the complex conductivity of dilute clay suspensions is measured using a four-point impedance measurement, which can be reliably calibrated in the frequency range between 0.1 Hz and 10 kHz. By using a minimal number of fitting parameters when reliable information is available as input for the model and carefully examining the issue of potential over-fitting, we found that our model can be used to fit the measured dispersion of the complex conductivity with reasonable parameters. The good match between the modeled and experimental complex conductivity dispersion allows us to argue that our simplified model captures the essential physics for describing the low-frequency dispersion of the complex conductivity of dilute clay suspensions.

Effect of Interaction between Clay Particles on the Viscosity of Dilute Clay Suspension under Dispersed Condition

Effect of Interaction between Clay Particles on the Viscosity of Dilute Clay Suspension under Dispersed Condition

Effect of OH −/Al 3+ and Al 3+/clay ratios on the adsorption properties of Al-pillared bentonites

In this work, the adsorption properties of Al-pillared bentonites were investigated by using phenol and 2-chlorophenol as model pollutants. The Al-pillared bentonites were prepared by the conventional method of pillaring involving the mixing of a dilute clay suspension with a dilute pillaring solution. To study the effect of textural changes on the adsorption properties, the adsorbents were prepared by using different OH −/Al 3+ and Al 3+/clay ratios. It was determined that the adsorbed amounts of phenol decrease with increasing OH −/Al 3+ and Al 3+/clay ratios. Adsorption of 2-chlorophenol on the adsorbent adsorbing the highest amount of phenol was studied. It was found that the amounts adsorbed are nearly same for both of the adsorbates at low equilibrium concentrations and a slight difference is observed at concentrations exceeding 60 mg/L. The adsorbed amounts were compared with the amounts adsorbed by hexadecyltrimethylammonium bromide (HDTMA)–bentonite. It was obtained through the modification of bentonite with hexadecyltrimethylammonium bromide, in an amount equivalent to 100% of cation exchange capacity of the clay. It was observed that the adsorbed amounts of phenol are approximately three times higher in the case of Al-pillared bentonite having 1.44 and 1.8 OH −/Al 3+ and Al 3+/clay ratios, respectively. This behavior is attributed to the high surface area. Although the adsorbed amounts of 2-chlorophenol on the Al-pillared bentonite are same with that of phenol, they are lower than the amounts adsorbed on HDTMA–bentonite and it was concluded that the existence of pseudo-organic layer is of importance in the case of the adsorbates having low water solubility and the form of the sample 1 modified with HDTMA will be more efficient.

Effect of Clay Mineral type on the Viscosity of Dilute Clay Suspension

Effect of Clay Mineral type on the Viscosity of Dilute Clay Suspension

Partitioning of Clay Colloids at Air–Water Interfaces

Colloid sorption onto air–water interfaces in a variety of natural environments has been previously recognized, but better quantification and understanding is still needed. Affinities of clay colloids for the air–water interface were measured using a bubble-column method and reported as partition coefficients (K). Four types of dilute clay suspensions were measured in NaCl solutions under varying pH and ionic strength conditions: kaolinite KGa-1, illite IMt-2, montmorillonite SWy-2, and bentonite. The K values of three types of polystyrene latex particles with different surface-charge properties were also measured for comparison. Kaolinite exhibited extremely high affinity to the air–water interface at pH values below 7. Illite has lower affinity to air–water interfaces than kaolinite, but has similar pH dependence. Na-montmorillonite and bentonite clay were found excluded from the air–water interface at any given pH and ionic strength. Positively and negatively charged latex particles exhibited sorption and exclusion, respectively, at the air–water interface. These results show the importance of electrostatic interactions between the air–water interface and colloids, especially the influence of pH-dependent edge charges, and influence of particle shape.

Remediation by artificial cooling of dilute clay suspensions contaminated by heavy metals

AbstractVertical freezing of clayey suspensions contaminated by heavy metals was conducted. A small unidirectional thermal gradient applied to a sample placed in a parallelopipedic cell led to the low-rate propagation of an upward freezing front. During this propagation, segregation of salts occurred and the non-solidified phase ahead of the freezing front became enriched with metallic salts. Moreover, some of the non-miscible particles in suspension were repelled by the freezing front. Therefore, the solidified phase became poorer with metallic pollutants bound to such nonmiscible particles as clayey colloids or complexes. Thus, artificial cooling was able to purify a suspension contaminated by heavy metals that exist in various chemical forms. This paper presents results for different experimental conditions and physico-chemical parameters such as the pH and the ratio between the concentrations of metallic cations and clay particles. The influence of these physico-chemical parameters on the speciations of lead and on the efficiency of this method is discussed. These freezing tests carried out on polluted soils should succeed in their remediation. This new method is called ‘cryoremediation’.

FLOCCULATION OF HOMOIONIC SODIUM PALYGORSKITE, PALYGORSKITE-MONTMORILLONITE MIXTURES AND PALYGORSKITE CONTAINING SOIL CLAYS

Flocculation of palygorskite has not been studied in detail. We have investigated flocculation of reference palygorskites, palygorskite-montmorillonite mixtures, and palygorskite containing soil clays. The flocculation values (FVs) of the clays were measured in a series of test tubes according to van Olphen (1977). The flocculation of the clays was determined visually by settling after 24 h of standing. Very dilute clay suspensions (0.066%) were taken for the tests. The FV of palygorskite at near neutral pH was significantly lower than that of montmorillonite. The FVs of four Na-palygorskites were in the range from 0.2 to 2.5 meq/L NaCl and the FV of Na-montmorillonite from Wyoming was 13.3 meq/L NaCl at pH ∼ 7. FVs of both palygorskite and montmorillonite increased with pH. The effect of pH on FV of palygorskite was more significant than that of montmorillonite. At pH ∼ 10.5, the FVs of all palygorskite samples were 25.0 meq/L NaCl, and the FV of the montmorillonite sample was 50.0 meq/L NaCl. Settling of clay particles was affected by concentration of clay in suspension. Settling was clearly observed in test tubes at a clay concentration of 0.066%. At a clay concentration of 0.666%, however, settling was not observed. The apparent contradiction between low FVs of palygorskite suspensions, obtained in the present study, and low rheological susceptibility of palygorskite muds to salts, known from industrial experience, can be explained by differences in clay concentration used for FV measurements and for industrial applications. FVs of palygorskite-montmorillonite mixtures at pH ∼ 7 increase with montmorillonite percentage in the mixture. At a specific concentration of montmorillonite in the mixture, the FV of the system attains the FV of pure montmorillonite and does not change with further montmorillonite addition. This montmorillonite concentration varied among the palygorskite samples and was in the range of 40 to 60%. FVs of three smectite- palygorskite- kaolinite-containing soil clays (from which carbonates, iron oxides and organic matter had been removed) at near neutral pH values were the same as FV of reference montmorillonite.

Flow characteristic of dilute Na montmorillonite suspension

The objective of this paper was to study the flow properties of dilute Na montmorillonite suspensions. Until now, a very dilute Na montmorillonite suspension has been treated as a Newtonian fluid. However, this paper shows a different behavior. Consistency curves of dilute suspensions, measured over different measuring times, may exhibit a different behavior from that of a perfect Newtonian fluid with a concentration of 33–36 kg/m 3. The simple viscoelastic model a Maxwell model proposed by the authors in a previous paper analyzes this behavior. The theoretical analysis predicted that the consistency curve measured in au extremely short measuring time shows negative shear-rate thixotropy, and the loop disappears as time increases. The experimental results confirmed the validity of the analysis. The consistency curves of a dilute clay suspension over extensive measuring times allow estimation of the relaxation time and the shear modulus of the suspension as well as the coefficient of viscosity.

Influence of Low Molecular Weight Polymers on the Rheology of Bentonite Suspensions

In this communication we demonstrate how relatively low molecular weight synthetic polymers significantly alter the rheological properties of Bentonite/water suspensions depending upon the polymer dosage and/or degree of surface coverage on the clay particle. The behaviour of two types of nonionic polymers are reported; a series of nonylphenol poly(propylene oxide) poly(ethylene oxide) polymers with varying EO chain length and a series consisting of an ABA block copolymer of poly(propylene oxide)-poly(ethylene oxide) with varying EO chain length. Adsorption isotherms of dilute clay suspensions showed a higher uptake of the lowest molecular weight polymer (in µmol/m²) for each series. The adsorbed amount G increases in the order NPE > PEO > PE. The oscillatory shear and steady state shear stress-shear rate measurements of concentrated clay suspensions (3-6% w/v) facilitate the interpretation of the particle-particle interactions. The yield stress, plastic viscosity and elastic modulus showed a maximum at about 50% surface coverage by the NPE polymers, and a subsequent decrease due to stabilisation of the suspension. For the PE polymers these parameters continously decreased as the surface of the clay particle was covered. Scaling of the elastic modulus with increasing clay content allows the determination of the exponent n from a power-law fit G = Kon which qualitatively describes the degree of dispersion for the different polymers. Preliminary results of the effect of temperature and pressure on Bentonite/polymer suspensions are also presented.

The Microstructure of Dilute Clay and Humic Acid Suspensions Revealed by Freeze-Fracture Electron Microscopy: A Reply

The Microstructure of Dilute Clay and Humic Acid Suspensions Revealed by Freeze-Fracture Electron Microscopy: A Reply

The influence of dilute clay suspensions on sea scallop ( Placopecten magellanicus) feeding activity and tissue growth

Long and short-term laboratory experiments were conducted to examine biological responses of sea scallops ( Placopecten magellanicus) to relatively dilute bentonite clay suspensions. The effect of bentonite addition (0, 2 and 10 mg·dm −3 treatments) to a natural diet of phytoplankton and organic detritus (seston) on somatic and reproductive tissue growth was examined over 68 days during the period of gametogenesis. Filtration, ingestion and pseudofaeces production rates and particle retention efficiency were measured for scallops which were fed mixtures of algae (dried Tetraselmis suecica) or natural seston and bentonite (0 to 15 mg·dm −3). Pre-ingestive particle-selection capabilities were examined through chlorophyll a, organic content and carbon and nitrogen analyses of suspended particles and pseudofaeces. The results indicate a low tolerance to suspended bentonite. Extensive chronic mortalities and significant impacts on somatic and reproductive tissue growth were exhibited at 10 mg·dm −3. Despite an inability to effectively retain clay-size particles, sea scallop feeding activity was altered by dilute bentonite suspensions. Animals fed natural seston without added bentonite displayed filtration rates twice as high as when 2 mg bentonite per dm 3 was added, but tissue growth in both groups was similar. When provided with a diet of Tetraselmis, a similar reduction in filtration rate required bentonite concentrations exceeding 6 mg·dm −3; levels lower than 1.0 mg·dm −3 enhanced filtration rates. Sea scallops displayed two feeding mechanisms for actively enhancing the quality of ingested matter when exposed to elevated levels of suspended clay. Scallops were less efficient at retaining bentonite particles at concentrations exceeding 2 mg·dm −3 than at lower levels. This shift in retention efficiency did not require a period of acclimation. Above a threshold bentonite concentration of 2 mg·dm −3, scallops produced pseudofaeces and selectively ingested seston or Tetraselmis over clay particles. Selection efficiencies, determined from relative chlorophyll a, AFDW, POC and the PN-concentration of retained particles and pseudofaeces, were low compared with values published for other suspension-feeding bivalves.

The Microstructure of Dilute Clay and Humic Acid Suspensions Revealed by Freeze-Fracture Electron Microscopy: Discussion

The Microstructure of Dilute Clay and Humic Acid Suspensions Revealed by Freeze-Fracture Electron Microscopy: Discussion

The Microstructure of Dilute Clay and Humic Acid Suspensions Revealed by Freeze-Fracture Electron Microscopy

The Microstructure of Dilute Clay and Humic Acid Suspensions Revealed by Freeze-Fracture Electron Microscopy

The origin of the swelling of clays by water

The diffuse electric double-layer formalism allows calculation of the swelling pressure in good agreement with the observations made on dilute clay suspensions. We correct an error often made in the calculations that renders them incoherent. Analysis of the energies of the clay-water-cation system suggests the importance of solvation of the interlamellar cations

Transport and deposition of dilute colloidal suspensions in soils

SUMMARYTransport and deposition of suspended particles occur during many soil processes. The mechanisms of removal of particles from suspension during saturated flow are described, and a simple equation of depth filtration is used to test experimental data. A method for labelling dilute clay suspensions with 14C‐paraquat is developed. Particles are removed from flowing suspension even when they are dispersed. The depth filtration equation holds only under these conditions, though the mechanisms of removal of particles from suspension by the soil are unclear. A surprisingly large reduction in flow rate accompanies passage of dilute clay suspensions through soil columns.

Decrease of hydraulic conductivity in sand at the interface between seawater and dilute clay suspensions

The hydraulic conductivity of the seawater—fresh groundwater interface zone in coastal aquifers may decrease due to: (1) deflocculation and (2) dispersion of small amounts of arrangements of reactive clay minerals that exist in the rock. This dispersed phase may influence to a large degree the connectivity between the conducting pores of a sediment. A reduction of hydraulic conductivity by 2–3 orders of magnitude was observed in analytically pure sand as well as in shore sand packed in columns when an interface between seawater and a dilute suspension of montmorillonite was created. The experiments were done by introducing suspensions of 5, 15, 30 and 60 mgl −1 of montmorillonite to columns in which a flow of seawater has previously been established. An amount of clay as small as 5 · 10 −3% was involved in the creation of low permeability. The proposed model for the explanation of the observed reduction of hydraulic conductivity assumes that at a certain stage the fluid begins to behave as a non-Newtonian fluid since loose networks of clay particles trap ∼99% of water, causing stoppage in the “bottlenecks” of the porous medium. As a consequence the overall sediment behaves as a “Bingham system”, with a yield stress. Coating of sand grains with clay is also assumed to occur in the case of concentrated suspension.

Interaction of clays with dilute fluoride solutions

Interaction between dilute (mg L−1) NaF solutions and clay suspensions (0.08 % w/v) has been examined as a function of pH (range 3 to 8), clay type (Na+- or Ca2+-kaolinite, illite, montmorillonite) and NaF concentration. No F loss from solution was detected at pH > 6.5, while enhanced uptake was found on decreasing the pH, especially in the 4 to 3 region. Removal of F from 1 to 6 × 10−4 M NaF was only slightly dependent on weight of solid, but did increase with [F−]. It is proposed that F losses are due to the formation of sparingly soluble Al species (e.g. cryolite, Na fluoro silicate), occasionally augmented with CaF2 formation (Ca2+-clays). The Al is released by proton attack on the lattice, following conversion of the suspended solids into the unstable H+-form, either through acid addition (pH < 5) or through hydrolysis of the Na+-form material. The latter process was most pronounced with the illite and montmorillonite samples. The amount of F fixed by montmorillonite was roughly double that held by the other two clays, and had a maximum value (pH 3) of ∼ 4 mg g−1, using 11 mg L−1 NaF solutions. Soluble fluoro-complexes, similar in quantity to the retained F, were detected, in many of the studies. It was concluded that contact of the clay components of soils or sediments with mg L−1 levels of F in adjacent aqueous phases would result in only a minor proportion being retained.

Preparation of a flocculant based on polyamides

AbstractA flocculant based on waste oligomers from the polycaprolactam production was synthesized by alkaline reduction with Ni/Al alloy. Both the reduced oligoamide and the sodium aluminate are precipitated by methanol. An oligomer, absorbed by a mineral carrier, is isolated as final product. The modified oligoamide was characterized by elemental analysis, IR spectra, and was shown to contain hydroxyl groups. The prepared flocculant may be used for the clarification of natural dilute (1%) clay suspensions and wastewaters. It accelerates the precipitation 35 times, giving a compact precipitate, which favors the decanting of the clarified liquid. The optimal concentration of the flocculant is 1.8 g/liter (corresponding to 0.06 g/liter oligomer).

Acid—base equilibria in clay suspension

The thermodynamics governing the equilibria of weakly basic compounds in dilute clay suspensions is developed in considerable detail. Quantities suitable for characterizing the equilibrium are shown to be: K eff, an apparent equilibrium constant for the acid—base reaction in suspension; Δ G ̄ BH + , and Δ G ̄ B , which are the changes in the partial molar Gibb's free energy for the protonated and neutral forms of the base B, respectively, which occur upon addition of clay to the system at constant T, P, and composition. The above thermodynamic treatment is then used to examine the frequently observed phenomenon that basic compounds in clay suspensions are often protonated to a much greater extent than that predicted on the basis of the pH of the bulk solution phase and the p K of the compound. It is shown that the enhanced protonation is due to the ability of the clay—water interface to significantly lower the potential of the protonated form of the molecule relative to that of the neutral form. This relative difference in stabilization of the two forms displaces the equilibrium and is shown by experiment to depend on the apparent magnitude of negative charge on the clay surface as encountered by the basic compound.

Molecular Weight of Montmorillonite from Optical Transmission Measurements

AbstractThe weight average molecular weight of small Na‐montmorillonite particles in aqueous suspension have been determined by means of optical density (OD) measurements. In the wavelength range of λ = 4000A to 6000A and in dilute clay suspension which obeys Beer‐Lambert Law, the slope of the straight line of log (OD) vs. log λ is proportional to the major dimension of the particles. Assuming a disc geometry and the number of unit layers in a clay particle, and working with suspension with a slope near −4, the weight average molecular weight was found by using light scattering theory. The results agree reasonably with other data from the literature.