Kinetic aspects of flocculation of bentonite clay in the presence of anionic and cationic acrylamide copolymers

The flocculation kinetics in aqueous-salt medium in the presence of anionic and cationic high-molecular-weight random acrylamide copolymers was studied in the hindered sedimentation mode, with a suspension of bentonite clay as example. The influence exerted on the flocculation parameters by the concentration and order of addition of ionic acrylamide copolymers taken in various combinations was analyzed.     

Preparation of alpha-alumina-supported mesoporous bentonite membranes for reverse osmosis desalination of aqueous solutions

In this study, mesoporous bentonite clay membranes approximately 2 microm thick were prepared on porous alpha-alumina substrates by a sol-gel method. Nanosized clay particles were obtained from commercial Na-bentonite powders (Wyoming) by a process of sedimentation, washing, and freeze-drying. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption-desorption were employed for membrane characterization. It was found that the content of solids, concentration of polymer binder, and pH value of the clay colloidal suspension had critical influences on membrane formation during the dip-coating process. The membranes were tested for reverse osmosis separation of a 0.1 M NaCl solution. Both water permeability and Na(+) rejection rate of the supported membranes were comparable to those of the compacted thick membranes reported in the literature. However, due to the drastically reduced membrane thickness, water permeance and flux of the supported membranes were significantly higher than those of the compacted thick membranes. It was also observed that the calcination temperature played a critical role in determining structural stability in water and desalination performance of the clay membrane.     

The colloidal stability of raw bentonite deformed mechanically by ultrasound

The present study examined the effect of sonication time on the particle–size and the colloidal stability (i.e. point of zero charge, PZC and zeta potential, ζ) of raw bentonite (RB) from Saudi Arabia. In this study, bentonite suspensions were sonicated for various time intervals (30, 60 and 120 min). The effect of sonication time on specific surface area and the colloidal stability behavior of bentonite at various pH and in presence of different NaCl concentration were investigated. The increased in lightness and brightness of bentonite suspension was observed during sonication experiment which could be attributed to the reduction in the particles size.With increasing sonication time the specific surface area increased and consequently the zeta potential of bentonite suspension increased. Also a shifting in the PZC from pH 3 for raw bentonite to pH 2 after 120 min of sonication.The zeta potential of sonicated bentonite suspension in presence of different concentration of NaCl shows unusual trend compared to the unsonicated bentonite. In conclusion, the stability of raw bentonite suspension was significantly modified due the application of ultrasound with rending the particle-size of the bentonite.     

利用分散稳定性分析仪研究水煤浆的稳定性

采用Turbiscan Lab浓缩体系分散稳定性分析仪研究了改性木质素系分散剂（GCL3S）和萘系分散剂（FDN）对水煤浆稳定性及浆体中煤颗粒沉降行为的影响。结果表明,水煤浆中煤粒沉降行为为差异沉降,在水煤浆制备过程中,煤颗粒之间会发生团聚,掺1.0％GCL3S的水煤浆清液区高度及平均沉降速率仅为掺FDN的68％,木质素系分散剂制备的水煤浆稳定性能优于萘系。分散稳定性分析仪不仅可以用于水煤浆的稳定性分析,还有助于揭示分散剂对水煤浆的稳定作用机理。     

The Enhanced MR Effect of Dense Magnetic Particles Suspensions Consisting of Superfine α-Fe Particles

It is reported that magnetorheological (MR) effect was enhanced when superfineα-Fe particles and other nanosize particles were added to suspensions of dense micron magnetic particles. The effect of adding superfine particles on dynamics shear stress, sedimentation stability and structure of solidified MR of magnetic suspensions were studied. The experiment showed considerable increase of shear stress and much stability of sedimentation when the suspension consisting of superfine particles. The enhanced MR effect by superfine particles dealt with the properties, weight ratio and scale of superfine particles.     

The temperature dependence of the stability of aqueous kraft lignin dispersions in the near-isoelectric state of its particles

The stability of dilute aqueous kraft lignin dispersions in a near-isoelectric state of its particles (pH 2) is studied in the temperature range of 0?C20°C. An extremal temperature dependence with a minimum in the region of 10°C is revealed for the stability. It is assumed that, in the examined temperature range, the observed effect is due to variations in the surface forces and a possible influence of the morphology of aggregates being formed on their sedimentation.     

Influence of Magnetic Field and Temperature on the Synthesis and Colloidal and Chemical Properties of Fe3O4

A magnetic field and temperature was shown to affect disperse composition, electrophoretic behavior, and aggregation stability of synthesized magnetite particles. When synthesis proceeds, a process of the nucleation of ultramicroscopic Fe₃O₄ particles prevails over a process of their aggregation. Here an electrostatic factor of stability of magnetite suspension plays an important role. An application of the magnetic field decreases the aggregation stability and increases the sedimentation rate of product particles.     

两性纤维素接枝共聚物在膨润土上的吸附

The adsorption property of a new amphoteric graft copolymer of carboxymethyl cellulose with acrylamide and dimethylamminoethyl methacrylate(CGAD) on bentonite particles was studied by the method of CdI2-starch coloring. The amount of adsorption increased with the increase of time or CGAD concentration, but decreased with the increasing concentration of added NaCl or added hexadecyltrimethylammonium choride (HDTMAC). The amount of adsorption was also found to be dependent on temperature. i.e. decreasing with the increasing temperature. The adsorption heat H was calculated by the relationship of temperature with the amount of adsorption. The X-ray diffraction showed that interlayer adsorption occurred in the bentonite.     

Characterization and determination of the thermodynamic and kinetic properties of p-CP adsorption onto organophilic bentonite from aqueous solution

The characterization of tetraethylammonium bentonite and the adsorption of p-chlorophenol (p-CP) onto organophilic bentonite (tetraethylammonium bentonite) was studied as a function of the solution concentration and temperature. The observed adsorption rates were found to fit first-order kinetics. The rate constants were calculated for temperatures ranging between 15.0 and 35.0 degrees C at constant concentration. The adsorption energy E and adsorption capacity q(m) for the phenolic compound adsorbing on organophilic bentonite were estimated using the Dubinin-Radushkevic equation. Thermodynamic parameters (Deltag(a), Deltah(a), Deltas(a)) were calculated by a new approximation from the isotherms of p-CP adsorption on organophilic bentonite. These isotherms were modeled according to Freundlich and Dubinin-Radushkevic adsorption isotherms. The amount of adsorption of p-chlorophenol on organophilic bentonite was found to be dependent on the relative energies of adsorbent-adsorbate, adsorbate-solvent, and adsorbate-adsorbate interactions.     

Enhancement of dispersion stability of inorganic additives via poly(sodium-4-styrenesulfonate) treatment geared to hydrogel applications

This study reports the preparation of poly(sodium-4-styrene sulfonate) (PSS) treated bentonite and clinoptilolite to prevent the agglomeration and sedimentation of these inorganic fillers during the preparation of hydrogel. For this purpose PSS treated fillers were prepared by using various techniques (dip and dry, hydrothermal, one-step ball milling and ultrasonication methods). The most suitable technique for preparing these PSS treated inorganic fillers (abbreviated as BP-dip and CP-dip) was the dip and dry method. BP-dip and CP-dip based polyvinyl alcohol/polyvinylpyrrolidone (PVA/PVP) composite hydrogels were prepared using the freeze/thawing method after the addition of one of BP-dip and CP-dip inorganic fillers in various amounts. The swelling properties, stability behaviors and Rhodamine B (RhB) adsorption of the composite hydrogels were studied. It was found that the swelling degrees of CP-dip and BP-dip based composite hydrogels with 25 mg of filler were higher than that of all other samples. The kinetic mechanism of RhB adsorption process and the related characteristic kinetic parameters were investigated by Pseudo kinetic models. The adsorption kinetics results for RhB adsorption were found best fitted with pseudo-second-order kinetics model. The maximum RhB adsorption capacity was determined to be for PVA/PVP-CP-dip25, which was 3.3 times higher than that of the unfilled PVA/PVP hydrogel.     

Spectrophotometric and flow ultramicroscopic study of the aggregation and sedimentation stability of aqueous dispersions of sulfate lignin in a pH range of 12.0–2.3

The aggregation and sedimentation stability of low-concentrated (10 mg/l) aqueous dispersions of sulfate lignin are studied by the spectrophotometry and flow ultramicroscopy methods in a wide pH range (12.0–2.3). Initial solution of sulfate lignin (pH 12.0) is shown to be a polydisperse system stable with respect to aggregation and sedimentation. As pH decreases up to 3.2, the sedimentation stability is retained, whereas a loss of aggregation stability resulting in an enlargement of initial fine particles invisible with a flow ultramicroscope and their transition into the visible size range are observed even at pH 11.0. In the course of time, the formed visible particles aggregate with a concomitant decrease in their total concentration. This process is even more pronounced at pH 10.0. At pH 2.3, the system loses its sedimentation and aggregation stability, and the visible particle concentration increases by tens of times compared to pH 12.0 then, the particles aggregate that results in a decrease in the total particle concentration. At any pH value, the systems studied are polydisperse that is most pronounced at pH 2.3.     

高效二氧化钛/膨润土复合材料的制备及光催化性能研究

提出制备高效二氧化钛/膨润复合光催化的新方法——焦硫酸钾熔融/浸渍法， 并通过改变二氧化钛/膨润土的配比、反应时间、熔融灼烧温度等得到最佳制备条 件，采用XRD和TEM对该材料进行了表征，证实TiO_2呈高度分散状态，并已渗入膨 润土层间结构，使层间距扩大，形成互不干扰的活性反应中心，在模拟染料废水中 ，对复合材料的光催化降解性能进行了研究，结果发现，采用焦硫酸钾熔融/浸渍 法制备复合材料具有很高的光催化效率，对活性艳红染料的降解性能进行了研究， 结果发现，采用焦硫酸钾熔融/浸渍法制备的复合材料具有很高的光催化效率，对 活性艳红染料的降解率达93.6%，明显优于纯氧化钛和其他类似材料。     

The Optical Characteristics Method of Sedimentation Stability for Dense Magnetic Particles Suspensions

A new method for characterization of dense magnetic particles suspension is presented. Spectrophotometric method to timing determination of amounts of settled micron magnetic particles in a dense particles suspension was used. When nano particles TiO2were added to the dense magnetic suspension, sedimentation stability of the system was evidently improved.     

Formation of polymeric toroidal-spiral particles

Compared to spherical matrices, particles with well-defined internal structure provide large surface to volume ratio and predictable release kinetics for the encapsulated payloads. We describe self-assembly of polymeric particles, whereby competitive kinetics of viscous sedimentation, diffusion, and cross-linking yield a controllable toroidal-spiral (T-S) structure. Precursor polymeric droplets are splashed through the surface of a less dense, miscible solution, after which viscous forces entrain the surrounding bulk solution into the sedimenting polymer drop to form T-S channels. The intricate structure forms because low interfacial tension between the two miscible solutions is dominated by viscous forces. The biocompatible polymer, poly(ethylene glycol) diacrylate (PEG-DA), is used to demonstrate the solidification of the T-S shapes at various configurational stages by UV-triggered cross-linking. The dimensions of the channels are controlled by Weber number during impact on the surface, and Reynolds number and viscosity ratio during subsequent sedimentation. We anticipate applications of the T-S particle in drug delivery, wherein diffusion through these T-S channels and the polymer matrix would offer parallel release pathways for molecules of different sizes. Polyphosphate, as a model macromolecule, is entrained in T-S particles during their formation. The in vitro release kinetics of polyphosphate from the T-S particles with various channel length and width is reported. In addition, self-assembly of T-S particles occurs in a single step under benign conditions for delicate macromolecules, and appears conducive to scaleup.     

Xanthan gum-coated soft magnetic carbonyl iron composite particles and their magnetorheology

The dispersion stability of carbonyl iron (CI)-based magnetorheological (MR) fluid was improved by coating soft magnetic CI particles with an environmentally benign biopolymer of xanthan gum to reduce the density gap between the medium oil and dispersed particles. The sedimentation test of the MR fluid showed that the xanthan gum/CI composite particles improved the sedimentation drawback of the pristine CI-based MR fluid. The rheological properties of the MR fluid were also examined using a rotational rheometer to observe the typical MR characteristics, such as yield stress and shear viscosity.     

Ca-Fe/bentonite载氧体煤化学链燃烧反应特性

以天然石膏粉、膨润土(bentonite)和Fe(NO3)3·9H2O为原料,通过机械混合造粒法制备了钙基复合载氧体。在小型流化床反应器中,水蒸气作为气化-流化介质,研究了温度、活性组分含量及循环次数对复合载氧体反应活性的影响,同时考察了不同煤种化学链燃烧反应特性。实验结果表明,CaSO4含量为60%,Fe2O3为活性助剂的CaSO4-Fe2O3/ben(Ca-Fe/ben)载氧体平均磨损速率为0.089%/h。反应温度为900℃时,碳转化率达到95%所需的时间为20.8min,CO2平均干基浓度为95.99%,表现高的反应活性。10次氧化/还原反应后,CO2平均干基浓度保持在80%,载氧体保持良好的循环反应活性。同时,实验发现高挥发分高灰分的煤种更适于煤的化学链燃烧,且CO2浓度均保持在90%以上。粒径分布曲线表明循环反应中载氧体表现强的抗磨损能力。     

α-Fe粉体浓悬浮体系的制备及磁流变效应

报道使用价格低廉的还原铁粉制备磁性粒子浓悬浮体系,对体系磁流变效应进行研究,并研究了磁性颗粒尺寸和氧化物对悬浮体系力学性质及沉降稳定性的影响.     

Structure and stability of silica particle monolayers at horizontal and vertical octane-water interfaces

Monolayers of silica particles at horizontal and vertical octane-water interfaces have been studied by microscopy. It is found that their structure and stability depend strongly on the particle hydrophobicity. Very hydrophobic silica particles, with a contact angle of 152 degrees measured through the water, give well-ordered monolayers at interparticle distances larger than 5 particle diameters which are stable toward aggregation and sedimentation. In contrast, monolayers of less-hydrophobic particles are disordered and unstable. Two-dimensional particle sedimentation has been observed in the case of vertical monolayers. The results have been analyzed with a simple two-particle model considering the sedimentation equilibrium as a balance between the long-range electrostatic repulsion through the oil, the gravity force, and the capillary attraction due to deformation of the fluid interface around particles. The value of the charge density at the particle-octane interface, 14.1 muC/m(2), found for the most hydrophobic particles is reasonable. It drastically decreases for particles with lower hydrophobicity, which is consistent with the order-disorder transition in monolayer structure reported by us before. The pair interactions between particles at a horizontal octane-water interface have been analyzed including the capillary attraction due to undulated three-phase contact line caused by nonuniform wetting (the contact angle hysteresis). The results are in agreement with the great stability of very hydrophobic silica particle monolayers detected experimentally, even at low pH at the point of zero charge of the particle-water interface, and with the aggregated structure of hydrophilic particle monolayers.     

Kinetics of thermal denaturation of human rhinoviruses in the presence of anti-viral capsid binders analyzed by capillary electrophoresis

In vivo, the icosahedral capsid of human rhinoviruses undergoes well-defined transitions during the infection pathway. Native virus, sedimenting at 150S, is converted to subviral particles with a sedimentation coefficient of 135S, which have lost the innermost capsid protein VP4. Upon release of the genomic RNA empty 80S capsids remain. Similar structural modifications are observed in vitro upon exposure to low pH and/or elevated temperature. Virions are stabilized against these transitions by various antiviral compounds, which bind to a hydrophobic pocket in the capsid protein VP1. Using capillary electrophoresis the kinetics of viral decay in the presence of such hydrophobic drugs was investigated. Assuming first-order kinetics, the increase of the time constant reflects the extent of stabilization. Exposure of the virions to 55 degrees C after presaturation with the antivirals increased the time constants (as compared to native virus) by a factor of 8-30, from a few minutes to several ten minutes. Denaturation of the stabilized capsid gave rise to heterogeneous material rather than to defined subviral particles. This was confirmed by electron microscopy and indicates that the structural modification of the virus follows a kinetically well-defined pathway which is disturbed by the drugs resulting in disorganized disruption of the virion.     

Conductometric and Gravimetric Studies of the Kinetics of Graphite Sedimentation in Aqueous Dispersions

The kinetics of graphite sedimentation in aqueous dispersions is studied using conductometric and gravimetric techniques. Triton X-305, a nonionic surfactant, is used to regulate the aggregation of hydrophobic graphite particles and to stabilize the system. The differences in the kinetics of the change in the weight and conductivity of sediments depending on the surfactant concentration are discussed. It is shown that insulating films of low conductivity are formed around particles at a concentration corresponding to coating of graphite particles with a monolayer of the surfactant and the conductivity of the sediments sharply decreases. At a higher surfactant concentration, which corresponds to the critical micellization concentration, compact sediments are formed; their conductivity first decreases and then increases in the process of restructuring. The change in the sediment structure as a function of the surfactant concentration is discussed.