Hydrophobic agglomeration kinetics of fine kaolinite particles in aqueous suspensions

The hydrophobic agglomeration kinetics of kaolinite has been studied through the in-situ turbidity meter measurement system. The effects of surfactant dosage, stirring rate and particle size on the hydrophobic agglomeration dynamics have been investigated. Appropriate surfactant concentrations provided the strongest hydrophobicity, modest stirring rate offered a higher agglomerates formation rate and a lower disruption rate, and smaller particles had lower energy barrier and higher attachment efficiency. The best hydrophobic agglomeration conditions have been determined and a kinetic model of hydrophobic agglomeration has been proposed by experimental results. The kinetic model has been turned out to be fitted to the dynamic process well and can characterize as well as assess the hydrophobic agglomeration kinetics appropriately.     

Ionic condensation and charge renormalization in colloidal suspensions

The very popular notion of effective or renormalized polyion charge is a concept of fundamental importance in the field of highly charged colloidal or polyelectrolyte solutions. In such suspensions, the electrostatic coupling between oppositely charged species induces a strong accumulation (or electrostatic “condensation”) of counterions in the vicinity of the macroion surface. The basic idea is thus to consider the structural colloid and the condensed counterionic shell as a whole which carries an effective charge, Z^eff, much weaker than the structural one, Z^str. Consequently, as long as what happens far from the colloid is concerned, all Debye–Hückel-like linearized approaches which fail to correctly treat the nonlinear condensation phenomenon can still be used if Z^str is more or less replaced by Z^eff. Beyond this basic idea, it remains to estimate a priori the value of Z^eff. It will be discussed how to deduce simple laws for the effective charge of spherical colloids from the Poisson–Boltzmann approach, analogous to Manning's law for linear polyelectrolytes. The validity of these laws will be tested, against more complete treatments. Lastly, it will be shown that while the notion of colloidal charge renormalization remains clear for dilute suspensions, it becomes incorrect at higher densities where the condensed counterionic shells overlap.     

煤系高岭岩中固定碳燃烧动力学特性

煤系高岭岩中可燃矿物与不可燃矿物的共生组合增加了可燃矿物燃烧的复杂性,研究这类燃料的燃烧特性对充分利用煤矸石资源有积极的意义。参照FCC催化剂结焦燃烧机理,基于一系列假设,建立了煤系高岭岩中固定碳燃烧反应模型—未反应收缩核模型。采用空气气氛下等温热重法研究了煤系高岭土中固定碳的燃烧反应。研究表明,低于700℃,反应的控制步骤是煤系高岭岩中固定碳燃烧界面化学反应。通过对非均一颗粒体系的未反应核收缩模型计算分析,获得煤系高岭岩中固定碳燃烧反应动力学参数,活化能(E)为100.12kJ/mol,频率因子(A)为2.27×106s-1。     

Application of TMA and DTA for study of the crystallization behaviour of SiO2 in the thermal transformation of kaolinite

TMA/DTMA with DTA studies on the thermal changes of kaolinite were performed with special emphasis on the crystallization behaviour of amorphous SiO₂. The results of four different physical techniques (semiquantitative XRD, DTA, TMA and DTMA) were clearly in good agreement with the fact that the 1420°C exotherm in DTA is due to silica crystallization.Thanks to Dr. B. K. Sarkor, Director of the Institute for his kind permission to publish the paper and to Mr. D. K. Ahosh for his needful suggestions.     

Speciation of aluminum in acidic natural water equilibria with mineral phase kaolinite by chemical equilibrium calculation

Aluminum is largely associated with aluminosilicate minerals such as kaoliniteAl,Si,Os(OH), within the earth's crustl. During the weathering, especially when the acidrain hastens the process, aluminum is released and thus becomes available tobiogeochemical processes. The elevated concentrations of aqueous aluminum causedetrimental consequences to plants, aquatic organisms and humans. Therefore, there havebeen considerable growing concerns in the aqueous chemistry of aluminum these years.'In …     

Detection of four different OH-groups in ground kaolinite with controlled-rate thermal analysis

The thermal behaviour of mechanochemically treated kaolinite has been investigated under dynamic and controlled rate thermal analysis (CRTA) conditions. Ten hours of grinding of kaolinite results in the loss of the d(001) spacing and the replacement of some 60% of the kaolinite hydroxyls with water. Kaolinite normally dehydroxylates in a single mass loss stage between 400 and 600°C. CRTA technology enables the dehydroxylation of the ground mineral to be observed in four overlapping stages at 385, 404, 420 and 433°C under quasi-isobaric condition in a self-generated atmosphere. It is proposed that mechanochemical treatment of the kaolinite causes the localization of the protons when the long range ordering is lost.This revised version was published online in November 2005 with corrections to the Cover Date.     

Influence of poly(ethylene oxide) brushes on the rheological properties of MgO colloidal suspensions in water

A combined experimental and multiscale simulation study of the influence of polymer brush modification on interactions of colloidal particles and rheological properties of dense colloidal suspensions has been conducted. Our colloidal suspension is comprised of polydisperse MgO colloidal particles modified with poly(ethylene oxide) (PEO) brushes in water. The shear stress as a function of shear rate was determined experimentally and from multiscale simulations for a suspension of 0.48 volume fraction colloids at room temperature for both bare and PEO-modified MgO colloids. Bare MgO particles exhibited strong shear thinning behavior and a yield stress on the order of several Pascals in both experiments and simulations. In contrast, simulations of PEO-modified colloids revealed no significant yielding or shear thinning and viscosity only a few times larger than solvent viscosity. This behavior is inconsistent with results obtained from experiments where modification of colloids with PEO brushes formed by adsorption of PEO-based comb-branched chains resulted in relatively little change in suspension rheology compared to bare colloids over the range of concentration of comb-branch additives investigated. We attribute this discrepancy in rheological properties between simulation and experiment for PEO-modified colloidal suspensions to heterogeneous adsorption of the comb-branch polymers.     

Leveraging collective effects in externally driven colloidal suspensions: experiments and simulations

In this review article, we focus on collective motion in externally driven colloidal suspensions, as well as how these collective effects can be harnessed for use in microfluidic applications. We highlight the leading role of hydrodynamic interactions in the self-assembly, emergent behavior, transport, and mixing properties of colloidal suspensions. A special emphasis is given to recent numerical methods to simulate driven colloidal suspensions at large scales. In combination with experiments, they help us to understand emergent dynamics and to identify control parameters for both individual and collective motion in colloidal suspensions.     

Understanding interactions in zeolite colloidal suspensions: A review

Over the last five years significant progress has been made in understanding interactions in zeolite colloidal suspensions by elucidating the molecular interactions between zeolite crystal surface and species such as water, cations, and organic templates. This is the outcome of multidisciplinary work involving the generation of experimental data concerning the magnitude of ζ-potential, the theoretical and experimental identification of the zeolite crystal surface structure, combined with theoretical models spanning different length scales.     

Temperature effects on the point of zero charge and isoelectric point of a red soil rich in kaolinite and iron minerals

The effects of temperature (373–1373 K) on the point of zero charge (PZC) and isoelectric point (IEP) of a red soil rich in kaolinite and iron minerals were studied. PZC values of the soil treated at 373 and 573 K indicated the presence of iron oxide. The soil calcined between 773 and 1173 K shows a PZC almost coincident with the respective values of kaolinite. At 1373 K, the PZC of the soil is nearer to the value of iron oxide. In the entire temperature range studied the PZC values were lower than the IEP values. An approach of PZC and IEP values was observed after a partial removal of iron oxide by the dithionite-citrate-bicarbonate (DCB) method. The analyses of the PZC and IEP values, of electron probe micro analysis (EPMA) data and of specific surface areas evidence a specific adsorption of iron oxide on kaolinite. Finally, the dissolution sequence of iron and aluminium contained in soil was determined using hydrochloric acid.     

Bi4B2O9晶体及其熔体结构的高温原位拉曼光谱研究

利用密度泛函理论计算了Bi₄B₂O₉晶体的常温拉曼光谱, 并通过与实验拉曼光谱对比, 对其振动模式进行了归属. 利用高温原位拉曼光谱研究了Bi₄B₂O₉从常温到750 ℃升温过程中微结构的变化. 随着温度的升高, 晶体的平均键长变长, 键角分布变宽, 熔化后晶体中的BiO₄和BiO₅多面体解体, BO₃构型则保持三配位不变. 运用量子化学从头算法模拟了Bi₄B₂O₉的熔体结构并与实验拉曼光谱进行了对比分析, 发现在Bi₄B₂O₉熔体中B原子团簇为孤立的BO₃构型, Bi ³⁺游离于BO₃之间, 并结合未参与形成BO₃的O原子起到平衡电荷的作用.     

Photocatalytic degradation of hydrocarbons by bentonite and TiO2 in aqueous suspensions containing surfactants

Organic substances (toluene, asphaltene dissolved in toluene) poorly soluble in water were solubilized by sodium dodecylsulfate (SDS) and the organic pollutants were mineralized together with the surfactants in diluted TiO₂ suspension by UV light. In concentrated aqueous suspension, crude oil was photodegraded on the surface of Na-bentonite and the photocatalyst TiO₂. Experiments have been carried out with Na-bentonite contaminated with crude oil mixed in a ratio of 1:1 with TiO₂ as well. The photooxidation processes were followed by total organic carbon content (TOC) and diffuse reflection infrared spectroscopy (DRIFT) measurements.     

Aluminium ions at polyelectrolyte interfaces. III. Role in polyacrylic acid/aluminium oxide and humic acid/kaolinite aggregate cohesion

Understanding the formation and breakup of humic acids and clays agglomerates is a difficult challenge owing to their complex nature. Thus, to progress in the study of the stability of such systems, attempts were made to replace the humic acid/kaolinite natural system by the polyacrylic acid/aluminium oxide synthetic system. Since the present investigation was dedicated to determine some characteristics of acidic soils which contain traces of aluminium ions, these ions were added to the adsorbent/polyacid systems as trace constituents. Initial and short-term phenomena related to the adsorption of humic and polyacrylic acids on aluminium oxide and kaolinite clay have been presented elsewhere. Here we present long-term phenomena regarding the formation and cohesion of oxide and clay aggregates formed in the presence of polyacrylic and humic acids, respectively. The results of electrophoretic mobility measurements demonstrated the amphipathic character of polymeric layers adsorbed on aluminium oxide and the amphoteric character of humic acid layers adsorbed on kaolinite. The long-term stability of the two colloidal systems was determined to evolve similarly despite the existence of the these typical characteristics. Received: 24 July 2000 Accepted: 20 December 2000     

The adsorption of salicylic acid onto γ-alumina and kaolinite from solution in hexane studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFT)

It was possible to determine the maximum loading of salicylic acid adsorbed onto γ-alumina and kaolinite clay after exposure to salicylic acid dissolved in hexane by examination using diffuse reflectance infrared Fourier transform infrared spectroscopy (DRIFTS). The maximum surface loading of salicylic acid (which resisted washing with fresh hexane) on γ-alumina was four times that observed using water as a solvent (approximately 3.0 compared with 0.7 molecules/nm²). Washing the sample with water removed the organic which was in excess to the maximum level observed for samples prepared with aqueous solution. The spectra of samples prepared with a loading up to the maximum observed with aqueous solution showed no significant differences to those of samples where the organic had been adsorbed from hexane (with the same surface loading). New peaks were observed for loadings greater than 1 molecules/nm², but the salicylic acid was still present as carboxylate (with no clear evidence for the carbonyl group). Salicylic acid adsorbed more readily to the surface of kaolinite from solution in hexane than from aqueous solution (up to maximum average loading of 2 molecules/nm²). Washing the samples with water removed the organic to a loading in the region of 0.2 molecules/nm², independent of the initial loading. Salicylic acid was adsorbed onto kaolinite as the carboxylate. The findings indicate that uptake is mediated by a surface water layer even in the absence of bulk water.