水蒸气对高岭土高温吸附铅的影响

使用沉降炉开展了水蒸气对高岭土高温吸附铅影响的实验研究，其中铅的形态为PbO和PbCl₂两种。首先研究了0-20%水蒸气对高岭土吸附PbO（1100-1300 ℃）和PbCl₂（800-1300 ℃）的影响规律，然后基于XRD、SEM和残余羟基率等分析，掌握了水蒸气影响高岭土高温吸附的机理。结果表明，水蒸气可以减少高岭土表面羟基的高温脱落，从而阻碍了PbO吸附、促进了PbCl₂吸附。综合高温下惰性莫来石的出现和高岭土孔隙结构的坍塌等因素，PbO和PbCl₂的最佳吸附温度分别为1200和1000 ℃。     

Effect of structural stress on the intercalation rate of kaolinite

Particle size in kaolinite intercalation showed an inverse reactivity trend compared with most chemical reactions: finer particles had lower reactivity and some of the fine particles cannot be intercalated. Although this phenomenon was noted in the early 1960s and several hypotheses have been reported, there is no widely accepted theory about the unusual particle size response in the intercalation. We propose that structural stress is a controlling factor in the intercalation and the stress contributes to the higher reactivity of the coarser particles. In this study, we checked the structural deformation spectroscopically and indirectly proved the structural stress hypothesis. A Georgia kaolinite was separated into nine size fractions and their intercalations by hydrazine monohydrate and potassium acetate were investigated with X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) analyses. The apical Si-O band of kaolinite at 1115 cm(-1) shifted to 1124 cm(-1) when the mineral was intercalated to 1.03 nm by hydrazine monohydrate, and its strong pleochroic properties became much weaker. Similar reduction in pleochroism was observed on the surface OH bands of kaolinite after intercalation. Both the bending vibrations of the inner OH group at 914 cm(-1) and of the surface OH group at 937 cm(-1) shifted to 903 cm(-1) after intercalation by hydrazine. A new band for the inner OH group appeared at 3611 cm(-1) during the deintercalation of the 1.03 nm hydrazine kaolinite complex. Pleochroism change in the apical Si-O band suggested the tetrahedra had increased tilt with respect to the (001) plane. The tilt of the Si-O apical bond could occur only if the octahedra had also undergone structural rearrangement during intercalation. These changes in the octahedral and tetrahedral sheets represent some change in the manner of compensation for the structural misfit of the tetrahedral sheet and octahedral sheet. As the lateral dimensions of a kaolinite particle increases, the cumulative degree of misfit increases. Intercalation breaks the hydrogen bonds between layers and allows for the structure to reduce the accumulated stress in some other manner. The reversed size effect on intercalation probably was not caused by crystallinity differences as reported in the literature, because the Hinckley and Lietard crystallinity indices of the four clay fractions were very close to each other. Impurities, such as dickite- or nacrite-like phases are not significant in the studied sample as suggested by the XRD and IR results, they are not the main reasons for the lower reactivity of the finer particles.     

Effect of mechanical treatment on the silicate lattice of kaolinite

X-ray diffraction, differential thermal and chemical analysis have been used to investigate the effect of mechanical treatment on the crystalline lattice of kaolinite. It was established that mechanical treatment leads to amorphization of the mineral and the release of hydroxyl water, but the continuity of kaolinite??s silicate lattice remains intact despite certain deformations, and the phase transformations of the mineral thus occur without any noticeable change in temperature.     

高岭石与水分子相互作用的理论研究

为从微观角度深入探讨单个水分子与高岭石最易解理晶面不同暴露末端的作用特点,本工作通过密度泛函理论的计算方法对不同吸附形态的水分子与不同暴露末端的稳定作用构型进行几何结构与电子结构分析.吸附能的计算结果表明水分子在铝氧八面体羟基作为暴露末端的表面上最稳定的吸附方式为水分子的氧原子和氢原子分别与相邻两个羟基的氢原子和氧原子...     

Effect of glass cullet on thermal properties of kaolinite

Waste compromises environmental preservation as well human health in many countries. Recycling is an alternative that sometimes represents the only economical activity for a significant population in the big cities. Almost 3% of waste materials in Brazil are vitreous. Ceramic production adding waste glass is possible with advantages of costs reduction associated to decrease on firing temperatures and to the raw material itself. At present paper up to 80 mass% of waste glass was added to clay. The sintering temperature decreased linearly and the shrinkage increased with glass content, an effect more pronounced for high glass amount.     

Theoretical estimates of the IR spectrum of water intercalated into kaolinite

Calculations at AM1, PM3, and HF/6‐31G levels of part of the IR spectrum of the water–kaolinite intercalated system based on a 96‐atom cluster of kaolinite with one water molecule are reported. Only the water molecule conformation is optimized. Frequencies and intensities for just the water vibrations and stretchings of four cluster hydroxyls were calculated through partial Hessian matrices and polar tensors obtained by numerical differentiation of energy gradients and dipole moment. The water molecule was found to attach to the cluster mainly through a double hydrogen bond to the siloxane inner surface, partially entering the siloxane ring hexagonal hole. Though the theoretical results predict that the water OH stretching frequencies decrease from the gas‐phase state to the intercalated state, they are still higher than expected with respect to the observed spectrum. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

Sorption studies of the interaction of water and 2-propanol with catalysts based on kaolinite

The interaction of water and 2-propanol with monocation-substituted crystalline and metaforms of Glukhovskoe kaolinite was investigated. It was shown that the nature of the exchange complex and the structure of the surface affect both the distribution of absorbed molecules of water on various segments of the surface in the first stages of its rehydration and the orientation of adsorbed molecules of 2-propanol. On crystalline forms of kaolinite a part of the alcohol molecules is oriented perpendicular to the surface, while on metaforms planar orientation of molecules is predominant.Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 26, No. 2, pp. 209–214, March–April, 1990.     

Effect of reaction temperature on intercalation of octyltrimethylammonium chloride into kaolinite

The structural property, thermal behavior, and morphology of octyltrimethylammonium chloride–kaolinite complexes prepared at different reaction temperatures were studied by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry–differential scanning calorimetry, and scanning electron microscope. The present study demonstrated that the arrangement model of octyltrimethylammonium cations (OTAC⁺) within the kaolinite interlayer space was independent of reaction temperature. The alkyl chains adopted a similar rigid paraffin-bilayer arrangement with different tilted angles. Although the intercalation led to an increased number of gauche conformers, the number of nonlinear conformers remained constant with increasing temperature. With increasing temperature, the number of trans conformers continuously augmented and resulted in decreased gauche/trans ratio. Therefore, the molecular environment remained solid like. Simultaneously, the surfactant packing density gradually increased, along with the decreasing water content in the organoclays. This effect improved thermal stability and hydrophobicity. The thermal decomposition processes of the kaolinite–OTAC⁺ complex can be divided into four steps. Furthermore, SEM images showed that the morphology of these complexes was strongly dependent on the given temperature. In general, increasing the temperature within the limited given temperature (≤70 °C) promoted the transformation from platy layers to nanoscrolls. Most of the transformed nanoscrolls were acquired in the products prepared at 70 °C, and further increasing in temperature decreased the nanoscrolls yield. Nevertheless, the packing density increased in the process, thereby demonstrating that the packing density not only promoted nanoscrolls transformation but also prevented the progress.

     

Controlled Rate Thermal Analysis of kaolinite dehydroxylation: effect of water vapour pressure on the mechanism

The present kinetic study is focused on one aspect of kaolinite dehydroxylation, namely the influence of water vapour pressure in the 10⁻³ to 5 hPa range and in the presence of crystalline defects. The experimental problem of keeping, throughout the dehydroxylation, the pressure gradients negligible around and within the sample is solved by means of Controlled Rate Evolved Gas Detection (CR-EGD). The dehydroxylation rate selected is as low as 0.014 h⁻¹ (which corresponds to a duration of 70 h for the whole experiment). Moreover, more than 20 independent measurements of the apparent Arrhenius energy of activation are carried out all along the dehydroxylation, with help of the rate–jump method, and therefore, without any assumption about the rate law of the determining step. In these conditions, the apparent Arrhenius energy of activation measured during the dehydroxylation of a poorly crystallised kaolinite is shown to be constant in the range 0.02<<0.84 (under 10⁻³ hPa) and in the range 0.18<<0.80 (under 5 hPa), indicating that the rate law obeys the Arrhenius law in this range of extent of reaction. The corresponding activation energies obtained are (233±15) kJ/mol under 10⁻³ hPa and only (188±10) kJ/mol under 5 hPa. Although this decrease is in contradiction with previously published results, it can be interpreted by considering that, under 10⁻³ hPa, diffusion is the limiting step whereas, under 5 hPa, the part of water desorption probably becomes predominant.     

Effect of salt modification on adsorption properties of acid-activated montmorillonite and kaolinite

Effect of modification of a layered aluminosilicate, montmorillonite, and rigid-structure kaolinite activated by sulfuric acid with solutions of magnesium chloride was studied in order to obtain sorbents for wastewater treatment to remove organic compounds.     

Effect of polyvinylpyrrolidone and sodium dodecyl sulphate on the dispersity and fluidity of concentrated kaolinite suspension

Flow curves for the concentrated suspension of kaolinite (20 g/30 ml-medium) were obtained in the presence of polyvinylpyrrolidone (PVP) and sodium dodecyl sulphate (SDS) by means of a Couette-type rotary viscometer. The flow curves were Newtonian or non-Newtonian, depending on the concentration of PVP and SDS added. From these curves, the plastic viscosity (_PL) and Bingham yield value (F₀) were obtained. The relative viscosity (_rel) of _PL with respect to the medium viscosity (₀) were calculated and the contour lines for F₀ and for _rel obtained as a function of the concentration of SDS and PVP added. The feature of these contour lines was qualitatively similar to that for the mean diameter (d_m) of the secondary particles in a dilute suspension of kaolinite. It was concluded that both the increase in d_m in the dilute suspension and the increase in _rel and F₀ in the concentrated suspension were brought about by the interparticle bridging effect of PVP. The increase in_rel was due to the formation of bulky flow units of large void volume. The increase in F₀ reflected the growth of gel structure caused by the bridging effect. It was shown that PVP behaved as a flocculating agent at lower concentrations, but behaved as a dispersing agent at higher concentrations, while SDS at any concentration behaved as a dispersing agent for kaolinite suspension.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occasion of his 60th birthday.     

Effect of complexing agents and surfactants on the sorption of Co(II) by kaolinite

The effect of pH on the removal of Co(II) by kaolinite both in the absence and presence of phosphate, citrate, oxalate and EDTA anions, and cationic and anionic surfactants have been investigated and the results obtained are compared with the precipitate formation curve of Co(II) calculated theoretically from published hydrolysis data of the metal ion. In general, the results indicate that the percent adsoprtion of Co(II) increases with the pH and that kaolinite has little affinity for anionic metal complexes. Both strong cationic and anionic surfactants decrease the percent removal of Co(II) by kaolinite but the reasons are different. On the other hand, the weakly ionized anionic surfactant, potassium stearate, enhances the adsorption of Co(II) by kaolinite. The results are discussed in terms of the hydrolysis of Co(II), the properties of kaolinite, and the possible interaction between the ligands tested and both Co(II) and the clay mineral.     

Adsorption of aspartic acid on kaolinite

The interaction of aspartic acid with kaolinite was studied by potentiometric titrations and by adsorption measurements both at constant aspartate concentration (but varying pH) and at a constant pH of 5.5. The temperature was 25 degrees C, and the ionic medium 5 mM KNO3. Aspartic acid dissociation constants estimated from titrations agreed with those from the literature. The adsorption of aspartic acid to kaolinite was weak and varied only slightly with pH; 10-18% of 100 microM aspartic acid adsorbed to kaolinite at 100 m(2)L(-1) between pH 3 and 10. Data from the titrations and adsorption experiments were fitted closely by an extended constant-capacitance surface complexation model, in which monodentate outer-sphere complexes formed between deprotonated aspartic acid molecules and protonated sites on the variable-charge edges of the kaolinite crystals. There appeared to be no adsorption to the permanently charged crystal faces.     

Stepwise dansyl grafting on the kaolinite interlayer surface

A block copolymer (PS-b-poly(l-Glu)) composed of polystyrene and poly(l-glutamic acid) was used as a stabilizer for dispersion polymerization of styrene. When dispersion polymerization of styrene was conducted at 70 °C in 80% dimethylformamide-water with 0.5 wt% PS-b-poly(l-Glu), spherical polystyrene particles with D_n = 0.72 μm and narrow size distribution were obtained. Whereas AIBN concentration did not have any effects on particle size, molecular weight of the polystyrene particles was strongly dependent on the initiator concentration. As concentration of the PS-b-poly(l-Glu) increased from 0.2 to 1.0 wt%, particle size decreased from D_n = 0.91 to 0.69 μm with keeping surface area occupied by one poly(l-glutamic acid) chain about S = 50 nm². On the other hand, an increase in initial concentration of styrene from 2 to 20 wt% caused an increase in particle size from D_n = 0.48 to 1.36 μm and a decrease in surface area per poly(l-glutamic acid) block from S = 91 to 45 nm². Colloidal stability of the polystyrene particles in aqueous solution was responsive to pH due to the surface-grafted poly(l-glutamic acid). For dispersion polymerization of styrene, the PS-b-poly(l-Glu) functions as both a stabilizer and a surface modifier.     

Thermodynamic aspects of the adsorption of hexametaphosphate on kaolinite

The adsorption of hexametaphosphate ion, an important deflocculant used in the ceramic industry, from aqueous solutions onto kaolinite has been studied at different temperatures. The adsorption isotherm follows the Langmuir model: the thermodynamic parameters DeltaG(ads)(0), DeltaH(ads)(0), and DeltaS(ads)(0) were calculated and found to be consistent with an interaction model involving the formation of an inner-sphere complex between HMP and aluminol groups. Also, the dependence of the adsorption behavior on the kaolinite volume fraction has been studied and discussed in term of association processes between the clay particles.     

Effect of polyvinylpyrrolidone and sodium lauroyl isethionate on kaolinite suspension in an aqueous phase

Suspension of concentrated kaolinite (20 g/30 ml-medium) in the presence of polyvinylpyrrolidone (PVP) and sodium lauroyl isethionate (SLI) was allowed to evaluate its degree of dispersion based on their rheological studies. Flow curves at low shear rate, measured by means of cone-plate method, showed a non-Newtonian flow. Plastic viscosity and Bingham yield value were derived from the flow curves. Relative viscosity, effective volume fraction and void fraction of secondary particle were also obtained. Results of dispersity and fluidity of the suspension were explained. PVP acted as a flocculant at a concentration lower than 0.1% but as a dispersant at a higher concentration. The presence of SLI could decrease both the Bingham yield value and suspension viscosity. Cooperative and competitive effects of PVP and SLI were found. Results indicated that SLI enhanced the degree of dispersion of kaolinite when PVP was less than 0.1%. The suspension, however, showed a maximum flocculation (i.e., aggregation) at 4 mM SLI when the concentration of PVP was higher than 0.1%.     

Effect of polycarboxylate ether comb-type polymer on viscosity and interfacial properties of kaolinite clay suspensions

The interactions between kaolinite clay particles and a comb-type polymer (polycarboxylate ether or PCE), so-called PCE super-plasticizer, were investigated through viscosity and surface forces measurements by a rheometer and a Surface Forces Apparatus (SFA). The addition of PCE shows a strong impact on the viscosity of concentrated kaolinite suspensions in alkaline solutions (pH=8.3) but a weak effect under acidic conditions (pH=3.4). In acidic solutions, the high viscosity measured is attributed to the strong electrostatic interaction between negatively charged basal planes and positively charged edge surfaces of clay particles. Under the alkaline condition, the suspension viscosity was found to first increase significantly and then decrease with increasing PCE dosages. The results from surface forces measurement show that PCE molecules at low dosages can bridge the kaolinite particles in the concentrated suspensions via hydrogen bonding, leading to the formation of a kaolinite-PCE "network" and hence an increased suspension viscosity. At high PCE dosages, clay particles are fully covered by PCE molecules, leading to a more dispersed kaolinite suspensions and hence lower suspension viscosity due to steric repulsion between the adsorbed PCE molecules. The insights derived from measuring viscosity and interfacial properties of kaolinite suspensions containing varying amount of comb-type super-plasticizer PCE at different pH provide the foundation for many engineering applications and optimizing industrial processes.