Zeta Potential Of Kaolinite Research Articles

Colloidal and Sedimentation Behavior of Kaolinite Suspension in Presence of Non-Ionic Polyacrylamide (PAM).

Colloidal behavior of kaolinite particles in water was investigated in this manuscript, without and with the addition of a polymer flocculant (non-anionic polyacrylamide (PAM)), using diverse imaging techniques in addition to LUMisizer. The addition of PAM was found to be causing the formation of bridges among particles thus increasing their settling rates to the bottom of the container. To assess the size of flocs and the potential morphology of PAM around particles and their clusters, the state of flocs formation and polymer distribution was analyzed through various microscopical techniques, namely scanning electron microscopy (SEM) and transmission electron microscopy (TEM). SEM and TEM results revealed that, in the absence of PAM, the floc structure of the sediment was loose and irregularly distributed, while the presence of PAM made the sediment structures greatly denser. Later, using LUMisizer, dynamic light scattering (DLS) and the zeta potential of kaolinite, sedimentation, and colloidal behavior of suspension came under scrutiny. Using LUMisizer, the maximum packing and settling rates of the particles were experimentally obtained as roughly 44 vol%; settling rates were estimated in 63-352 µm/s when centrifugal force varied and, using maximum packing values, compressive yield was estimated to vary between 48-94 kPa. The results of this study are instructive in choosing appropriate polymers and operating conditions to settle clay minerals in tailing ponds. Additionally, the maximum packing of kaolinite particles was simulated with spherical particles with varied polydispersity to connect DLS data to the maximum packing values obtained using LUMisizer; the little discrepancy between simulation and experimental values was found to be encouraging.

Direct Orange 34 dye fixation by modified kaolin

ABSTRACTThe present study investigated the adsorption behaviour of Direct Orange 34, a highly toxic dye used in textile industries in Tunisia, on modified kaolinite-rich clays. A kaolin from the Sidi Bader (SDB) area was activated with hydrochloric acid to create the activated clay referred to hearafter as SDBa, or treated with FeSO4•7H2O to obtain its Fe-saturated form, Fe-SDB. The adsorbents were characterized by X-ray diffraction, X-ray fluorescence, transmission electron microscopy, BET surface area and zeta-potential measurements. The equilibrium adsorption data were analysed using the Langmuir and Freundlich isotherms. The estimated adsorption capacities (qm) for the dye were improved in the Fe-loaded samples. The good fit (R2 = 0.99) with a pseudo-second order expression suggests that the adsorption process could be effective following a chemisorption mechanism. At acidic pH, the optimum dye-retention rate was achieved for SDB (83%) after 60 min. The uptake decreased at neutral pH and increased again in alkaline media. This behaviour might be explained by the formation of covalent bonds between the OH radicals on the external surface and the negatively charged dye molecules. On the other hand, Fe impregnation increased the zeta potential of kaolinite, leading to a greater adsorption capacity compared to its natural and acid-activated counterparts. In addition, the adsorption rate increased when increasing the suspension temperature from 283 to 313 K. The modified kaolinite-rich materials showed satisfactory affinity for adsorbing this reactive dye.

Impact of pore water conductivity and porosity on the electrical conductivity of kaolinite

The purpose of this study is to quantify the magnitudes of surface conduction and pore water conduction from the measured electrical conductivity of kaolinite, with the ultimate goal of estimating the electrical conductivity of kaolinite with a wide range of pore water conductivities (σw = 0.013–3.356 S/m) and porosities (n = 0.368–1.0). Therefore, the theoretical background of the electrical conductivity in soils was reviewed, and electrical conductivity measurements on kaolinite were performed using both slurry and consolidation tests in this study. The results of this study demonstrate that the variations of measured electrical conductivity (σmix) with n are debatable according to the values of σw, because a decrease in n results in both an increase in surface conduction (Ks) and a decrease in pore water conduction (Kw); this causes the relative magnitude of Ks compared to that of Kw to vary with σw and n. Consequently, this study develops the relation between the porosity-normalized Ks/Kw and 1/σw. Additionally, the surface conductivity of the tested kaolinite is back-calculated and compared with the previous relationship between Ks and zeta potential of kaolinite. The measured and estimated σmix values are compared with the varying pore water conductivity and porosity values.

Deposition and Survival of Escherichia coli O157:H7 on Clay Minerals in a Parallel Plate Flow System

Understanding bacterial pathogens deposition and survival processes in the soil-groundwater system is crucial to protect public health from soilborne and waterborne diseases. However, mechanisms of bacterial pathogen-clay interactions are not well studied, particularly in dynamic systems. Also, little is known about the viability of bacterial pathogens when attached to clays. In this study, a parallel plate flow system was used to determine the deposition kinetics and survival of Escherichia coli O157:H7 on montmorillonite, kaolinite, and goethite over a wide range of ionic strengths (IS) (0.1-100 mM KCl). E. coli O157:H7 deposition on the positively charged goethite is greater than that on the negatively charged kaolinite and montmorillonite. Although the zeta potential of kaolinite was more negative than that of montmorillonite, kaolinite showed a greater deposition for E. coli O157:H7 than montmorillonite, which is attributed to the chemical heterogeneity of clay minerals. Overall, increasing IS resulted in an increase of E. coli O157:H7 deposition on montmorillonite and kaolinite, and a decrease on goethite. Interaction energy calculations suggest that E. coli O157:H7 deposition on clays was largely governed by DLVO (Derjaguin-Landau-Verwey-Overbeek) forces. The loss of bacterial membrane integrity was investigated as a function of time using the Live/Dead BacLight viability assay. During the examined period of 6 h, E. coli O157:H7 retained its viability in suspension and when attached to montmorillonite and kaolinite; however, interaction with the goethite was detrimental. The information obtained in this study is of fundamental significance for the understanding of the fate of bacterial pathogens in soil environments.

Effect of Stabilizer Reagents on Zeta Potential of Kaolinite and Its Relevance to Electrokinetic Treatment

The influence of the dispersion of pH and concentration of chemicals on zeta potential of kaolinite were investigated. Adding the cationic species led to an increase of the zeta potential, contrary to measuring done in water. The results proved that even a very low concentration of the cationic species (0.001 mol/L) causes a remarkable change of the zeta potential. The zeta potential of the kaolinite soils varied from 204.6 to −41.9 mV, according to the chemical reagents and electrolyte concentration. Moreover, the negative charge in kaolinite soils is highly pH dependent and surface charge of pure kaolinite is dropped to zero, (pHpzc) at pH 3.2–3.5. The greater electrolyte concentration resulted in the thicker diffuse double layer and higher pH at the iso-electric point. While, for some reagents there was no isoelectric point that to be observed, increase the pH at isoelectric point and Na2CO3 as well as CH3COONa led to decrease in pH at iso electric point of suspension kaolinite. Results revealed that presence of low molecular weight CaCl2, , H3PO4, Na2Sio2, CH3COONa, and Na2CO3 led to a increase in diffuse double layer thickness in order of CaCl2, , Na2CO3 and H3PO4, and Na2SiO4, and electrolyte concentration has important effect on such incrasing. Based on results of ζ and pH observed from using different cationic species, those pHpzc which are more close to the soil pH (ζ is dropped to zero) are more succeptible to be chosen as best reagent to stabilizing soil.

The Dispersive Effect of Sodium Silicate on Kaolinite Particles in Process Water: Implications for Iron-Ore Processing

AbstractKaolinite is a common gangue mineral in iron ore and sodium silicate has been used widely as a dispersant of silicate gangue minerals including kaolinite in various iron-ore flotation methods over a wide range of pH. Its actual dispersive effect on kaolinite under iron-ore flotation conditions has received very limited attention, however. The presence of hydrolyzable metal cations in process water further complicates sodium silicate—kaolinite interactions. In the present study, the dispersive effect of sodium silicate on kaolinite particles in distilled water as well as in CaCl2 and MgCl2 solutions was investigated systematically through electrophoretic mobility and colloid-stability studies. The studies were based on controlled pH, which eliminated the dispersive effect of sodium silicate induced by increasingpulp pH, in order to simulate the conditions of iron-ore processing. With pH controlled at constant levels, sodium silicate dispersed kaolinite only when positively charged sites were present on kaolinite surfaces and the zeta potential of kaolinite was more negative than ~−30 mV. Over the pH range from 5 to 10.5, a significant dispersive effect of sodium silicate was only observed at pH 7. In process water, when Ca and Mgwere present, the strong coagulation of kaolinite particles caused by the hydrolyzable metal cations could not be dispersed effectively with sodium silicate.

Using secondary additives to enhance the physicochemical properties of kaolinite

The adsorptions of various electrolytes namely; CH3COONa, H3PO4, Na2Sio3, Na2Co3, CaCl2, and Al2(SO4)3, onto kaolinite from aqueous solutions were investigated using zeta potential test. Based on zeta potential results, 36 different binders were designed using Na2Sio3 as well as H3PO4 as main stabilizers mixed with CaCl2 and Al2(SO4)3 as secondary additives at various electrolytes. Moreover, unconfined compressive strength (UCS) was used to find the undrained shear strength (USS) of treated kaolinite. From the experimental results, (i) pH strongly alters the zeta potential of kaolinite; (ii) The zeta potential of the kaolinite soils varied from 204.6 to -41.9 mV, based on the used chemical reagents as well as their concentration; (iii) Some of the electrolytes are able to change the interface charge from negative to positive for kaolinite; (iv) Thicker eiffuse double layer (EDL) as well as higher pH at the PZC resulted from the greater electrolyte concentration. Based on the results of zeta potential and pH observed from using different cationic species, those PZC which are more close to the soil pH are more succeptible to be chosen as the best reagent to stabilizing soil. Also, batch test results clearly showed the importance of using both CaCl2 and Al2(SO4)3 electrolytes as secondary additives in EK injection systems. Key words: Electrical double layer (EDL), kaolinite, zeta potential, point of zero charge (PZC).

The behavior of N,N-dipropyl dodecyl amine as a collector in the flotation of kaolinite and diaspore

The flotation behaviors of kaolinite and diaspore were investigated using N,N-dipropyl dodecyl amine (PN). Maximum recoveries of kaolinite and diaspore were about 90% and 50%, respectively. Both recoveries of kaolinite and diaspore increased with the increasing dosage of PN. On the basis of the zeta potential and FT-IR spectra, the ionization of surface hydroxyl and the isomorphic exchange of surface ions account for the charging mechanisms of surfaces of kaolinite and diaspore. The adsorption mechanism of PN on the surface of two minerals was mainly electrostatic. After reacting with PN, the zeta potential of kaolinite and diaspore both increased, and comparing with the original zeta potentials, potential of kaolinite increased much more than that of diaspore, this can explain why recovery of kaolinite is higher than that of diaspore.

A study of factors affecting on the zeta potential of kaolinite and quartz powder

The purpose of this study was to determine the effects of pH, ion type (salt and metal cations), ionic strength, cation valence, hydrated ionic radius, and solid concentration on the zeta potential of kaolinite and quartz powder in the presence of NaCl, KCl, CaCl2, CuCl2, BaCl2, and AlCl3 solutions. The kaolinite and quartz powder have no isoelectric point (iep) within the entire pH range (3 < pH < 11). In the presence of hydrolysable metal ions, kaolinite and quartz powder have two ieps. As the cationic valence increases, the zeta potential of kaolinite and quartz powder becomes less negative. Monovalent cation, K+, yields more negative zeta potential values than the divalent cation Ba2+. As concentration of solid increases, the zeta potential of the minerals becomes more positive under acidic conditions; however, under alkaline conditions as solid concentration increases the zeta potential becomes more negative. Hydrated ionic radius also affects the zeta potential; the larger the ion, the thicker the layer and the more negative zeta potential for both kaolinite and quartz powder.

The Use of Neural Networks for the Prediction of Zeta Potential of Kaolinite

The sign and the magnitude of the zeta potential must be known for many engineering applications. For clay soils, it is usually negative, but it is strongly dependent on the pore fluid chemistry. However, measurement of zeta potential time is time-consuming and requires special and expensive equipment. In this study, the prediction of zeta potential of kaolinite has been investigated by artificial neural networks (ANNs) and multiple regression analyses (MRAs). To achieve this, ANN and MRA models based on zeta potential measurements of kaolinite in the presence of salt and heavy metal cations at different pH values have been developed. The results of the models were compared with the experimental results. The performance indices, including coefficient of determination, root mean square error, mean absolute error, and variance, were used to assess the performance of the prediction capacity of the models developed in this study. The obtained indices make it clear that the constructed ANN models were able to predict zeta potential of kaolinite quite efficiently and outperformed the MRA models. Results showed that ANN models can be used satisfactorily to predict zeta potential of kaolinite as a rapid inexpensive substitute for laboratory techniques.

Settling of Kaolinite in Different Aqueous Environment

Settling characteristics of soils carry great importance for geotechnical engineers since sediments properties are formed during the settling of soil particles in an aqueous environment. In this study, settling characteristics of kaolinite are investigated. Different ionic strengths of NaCl, CaCl2 and AlCl3 were considered as a function of pH in aqueous environment of varying solid concentrations. Factors affecting the settling characteristics and fabric of kaolinitic sediments have been identified. The results of the study reveal that kaolinite settles in either flocculated or dispersed forms depending on pH and ion concentration. Flocculated settling occurs in acidic pH due to formation of flocs in edge-to-face structure with increasing positive charges at the particle edges. Dispersed settling occurs in alkaline pHs when ionic strength is low. When ionic strength is increased in alkaline pHs, kaolinite particles settle in flocculated form. Furthermore, the results show that pH has a significant role on the final sediment thickness or void ratio of kaolinite. Densely packed structures in alkaline and loosely packed structures in acidic aqueous environments are formed depending on pH level. Results also show that as the solid concentration increases, the settling rate decreases due to buoyancy effect. Finally, the zeta potential of kaolinite is correlated with the final sediment thickness or void ratio of kaolinite as a function of pH. This correlation proves that there is a good agreement between zeta potential and the final sediment thickness or void ratio, especially when the soil is settled in a dispersed form.

The role of physicochemical processes in controlling sediment transport and deposition in turbidity currents

Experimental results are presented that illustrate the role of chemical and electrostatic particle–particle interactions in controlling sediment transport in turbidity currents. These experiments were conducted in a small laboratory channel to allow good control of the background water chemistry. Both kaolinite clay and silica particles were used to generate the turbidity currents, and both sodium and calcium chloride were used to prepare background solutions with a wide range of ionic strengths (salinities). The zeta potential of kaolinite was found to vary considerably under the range of experimental conditions used, and this produced a significant variation in the size distribution of these particles. As a result, kaolinite deposition from the turbidity current increased greatly with background salt concentration. Silica remained highly negatively charged under all experimental conditions, and the behavior of silica turbidity currents did not change with salinity. These results demonstrate that the behavior of turbidity currents is dependent on the composition of the associated sediments and the background water chemistry.

Characterization of NOM adsorption to clay minerals by size exclusion chromatography

Mineral-bound humic substances modify the surfaces of clay minerals, changing the nature and number of adsorption sites for contaminants. Due to their effect on the surface charge of colloidal particles they can also change the particles mobility and thus their transport behavior. In this paper the influence of natural organic matter on the zetapotential of kaolinite and montmorillonite is shown. Adsorption experiments with kaolinite and montmorillonite show that due to adsorption the humic substances are fractionated. The equilibrium pH value does not influence the fractionation due to adsorption. Large hydrophobic molecules showed the strongest affinity towards the clay surfaces. Substances with a small apparent molecular size and a high content of carboxylic functional groups made up the non-adsorbing fraction of the NOM. Ca 2+ had no measurable effect on the adsorption. The low influence of the adsorbed NOM on the zetapotential of the clay minerals suggests physical adsorption as the predominant adsorption mechanism.

Electrophoresis and zeta potential of kaolinite

The effects of such parameters as preparation technique, pH, and sodium chloride concentration on the electrophoretic mobility of sodium kaolinite are examined using the single-particle microelectrophoresis technique. Cylindrical microelectrophoresis cells are shown to give misleading results and flat cells are used throughout. Theories regarding the surface electrical properties of kaolinite are discussed, and a method is proposed for calculating face zeta potential from experimental mobility. The method is based on an estimate of the edge zero point of charge. The Gouy—Stern—Grahame model was found to fit experimental data only after unrealistic adjustment of some model parameters.