Compression Of Double Layers Research Articles

Comprehensive investigation into in-situ chemical oxidation of ferrous iron/sodium percarbonate (Fe(II)/SPC) processing dredged sediments for positive feedback of solid–liquid separation

Before disposal of dredged sediments (DS), filtrating DS is commonly used for their volume reduction. The work, for the first time, investigated Fe(II)/SPC processing DS to advance their solid–liquid separation from filtering feasibility, operational mechanism, technic reinforcement to potential implication. 16 mg Fe(II)/TSS & 60 mg SPC/TSS treatment elevated solid content of DS from 25.7% to 55.7% (vacuum filtration for 10 min), along with filtrate volume increased from 45.0 mL to 77.5 mL. •OH and Fe(III) with their hydrolyzed polymers, from Fe(II)/SPC system, are mainly lying behind the improved solid–liquid separation. Detailedly, the dilapidation of extracellular polymeric substances (EPS) with the destruction of biomolecules in EPS was completed by •OH invasion, which might rearrange the extracellular/intracellular protein configuration, with the increments of β-sheet & random coil but the decrement of α-helices. Simultaneously, Fe(III) and their hydrolyzed polymers promoted the relief of electrostatic repulsive-forces and the squeezing of double-electric layers, and the gathered DS could be held by integration of Fe(III) with –COOH and –OH. Additionally, CaO strengthened the filtering velocity/extent of Fe(II)/SPC-treated DS. After 70 mg/g CaO treatment, its solid content further elevated to 61.7% after vacuum filtration for 5.5 min, mainly resulting from skeleton construction by CaO, charge neutrality by released Ca2+, bridging cell debris and biopolymers by released Ca2+, compression of colloids double layers by released Ca2+, and binding PO43- in outer centrate liquid by released Ca2+.

Immobilization of elemental mercury by biogenic Se nanoparticles in soils of varying salinity

Salinity can be a significant environmental stress which can govern the fate of nanoparticles in the environment as well as other factors such as pH, natural organic matter and minerals. In this research, the effects of salinity on the behavior of biogenic selenium nanoparticles (BioSeNPs) and consequences for elemental mercury (Hg0) immobilization in soil and soil solutions were investigated. It was found that homoaggregation and sedimentation of BioSeNPs were enhanced significantly with increasing salinity. Compression of the electric double layers of BioSeNPs at high ionic strengths resulted in attractive van der Waals forces dominating and leading to enhanced aggregation. Moreover, neutralization of the surface negative charge of BioSeNPs by divalent cations and the bridging of BioSeNPs via calcium binding to surface functional groups were also associated with enhanced aggregation. Such enhanced aggregation exerted inhibition of Hg0 immobilization in soil solutions/soils of varying salinity. These results indicate that salinity is an important environmental factor governing aggregation of BioSeNPs and therefore influencing the efficiency of Hg0 immobilization, and possible remediation treatments, as a consequence.

Understanding Interactions between Clay and Model Coal Surfaces in Electrolyte Solutions by a Quartz Crystal Microbalance with Dissipation Study

Clay slime coating is known to have a negative impact on coal flotation. It is therefore of great importance to study interactions between clay and coal under flotation conditions. In this study, the effect of electrolytes on the interactions of montmorillonite (MMT) clays with carbon or asphaltenes on sensor surfaces of quartz crystal microbalance with dissipation (QCM-D) as model coal was investigated. Ion beam sputtering deposition and spin coating methods were used to prepare carbon and asphaltene (a class of natural polyaromatic compounds) surfaces. The prepared surfaces were characterized by Raman spectroscopy. QCM-D was used to determine in situ interactions between MMT clays and model coal surfaces in electrolyte aqueous solutions. The MMT clays were shown to deposit significantly on the model coal surfaces only in the presence of NaCl or CaCl2 as a result of the compression of electrical double layers. Moreover the enhanced deposition by calcium ions is stronger than by sodium ions. The results f...

Transformation of CuO Nanoparticles in the Aquatic Environment: Influence of pH, Electrolytes and Natural Organic Matter.

Many studies have shown the effect of solution chemistry on the environmental behavior of metal-based nanoparticles (NPs), except CuO NPs. Here, we investigated the agglomeration, sedimentation, dissolution, and speciation of CuO NPs by varying pH, ionic strength, ionic valence, and natural organic matter (NOM). The results showed that as the pH moved away from 6, the size of CuO agglomerates decreased, along with the enhanced NP suspension stabilization, due to the increase of electrostatic repulsive force. Increasing ionic strength and valence intensified the agglomeration and sedimentation of CuO NPs because of the compression of electrical double layers. The presence of humic acid and citric acid enhanced the dispersion and stabilization of CuO NP suspension, but l-cysteine showed a different impact. Decreasing pH, increasing ionic strength and all NOM improved the dissolution of CuO NPs, but the divalent electrolyte (CaCl2) inhibited the Cu2+ release from CuO NPs compared to the monovalent electrolyte (NaCl). In addition, X-ray absorption near edge structure (XANES) analysis demonstrated that the presence of l-cysteine transformed more than 30% of CuO NPs to Cu(I)-cysteine by coordinating with thiol group. This study can give us an in-depth understanding on the environmental behavior and fate of CuO NPs in the aquatic environment.

Transport of graphene oxide in saturated porous media: Effect of cation composition in mixed Na–Ca electrolyte systems

The influence of cation composition in mixed Na–Ca electrolyte systems on the transport of graphene oxide particles in saturated porous media was studied. Column experiments were conducted to elucidate the transport behavior of GO by varied molar ratios of Ca2+/Na+ but of constant ionic strength (IS). The results show that retention of GO in sand column is strongly dependent on IS in the presence of Ca2+, featuring serious deposition rates (Rd) at the higher IS of 10mM. The maximum Rd was 48.22% at 1mM and 98.53% at 10mM. However, there was no obvious difference in GO retention in solutions that only contained Na+ when the IS increased from 1 to 10mM, and the Rd was 35.17% and 38.21% respectively. The molar ratio of Ca2+/Na+ in solution was much more influential in altering the particle retention behavior at the higher IS of 10mM, compared with little influence at 1mM. It was supposed that compression of diffuse double layers mainly controlled GO deposition under lower IS, while charge neutrality and metal (Ca2+) bridging played a significant role at the higher IS. A numerical advection–dispersion–retention model considering the combined processes of Langmuirian dynamics blocking and depth-dependent straining was successfully developed to simulate the transport process of GO through the sand column. Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energy calculations were also performed to better understand the mechanisms of GO mobility. Coupling analysis of breakthrough experiments, DLVO theory and numerical modeling in this work provides insight into the mechanisms of GO transport in saturated porous media and is useful for reliable prediction of nanoparticle penetration through the vadose zone.

Particle ordering in colloidal thin films deposited by flow‐coating

The wide applications of two‐dimensionally ordered nanoscale features have stimulated the development of cheap and fast fabrication techniques in recent years. We achieved large area of uniform film of nanoparticles between 49.8 ± 8.7 and 117.6 ± 6.7 nm via flow‐coating. However, the single crystalline domains of a close‐packed monolayer remained limited. That motivated deposition of initially ordered colloidal dispersions, attained through deionized solutions to extend electrostatic double layers for long‐range repulsion. Although the deposition agreed reasonably well with our power‐law model, the initial order was destroyed at high shear. While the particle order was partially preserved during deposition at low shear, the domain size was not particularly extensive due to the high compression of double layers during evaporation. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1287–1302, 2014

Adsorption Behavior of Perfluorochemicals (PFCs) on Boehmite: Influence of Solution Chemistry

Abstract With global distribution, persistence nature, and strong bioaccumulation, the fate and transport of perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) in natural environment have recently attracted strong attentions. As boehmite is a common form of hydrated aluminum oxide existing in soils and sediments, this study successfully revealed the adsorption behavior of PFOS and PFOA on boehmite and the influence from solution chemistry. The results of kinetic experiments show that the adsorption equilibrium can be achieved within 48 hours and the boehmite surface is generally receptive to PFOS and PFOA adsorption. The adsorption isotherms estimated the maximum adsorption capacities of PFOS and PFOA on boehmite to be 0.877 μg/m 2 and 0.633 μg/m2, respectively. The increase of pH can lead to a moderate decrease of PFOS and PFOA adsorption, owing to the increase of ligand exchange reaction and the decrease of electrostatic interaction. With the compression of electrical double layers, the competitive adsorption from the other ions and the Ca2+ bridging effect between perfluorochemicals have demonstrated their negative influence for PFOS and PFOA adsorption on boehmite surface. Finally, humic acid (HA) also showed significant retardant effects on the sorption of perfluorooctanesulfonate (PFOS) and perfluorobutanesulfonate (PFBuS) on boehmite.

Ionic Concentration Effects on Reverse Micelle Size and Stability: Implications for the Synthesis of Nanoparticles

We present a systematic investigation and analysis of the structure and stability of reverse micelle systems with the addition of NH(4)OH, ZrOCl(2), and Al(NO(3))(3) salts. We demonstrate that the reverse micelle size decreases with increasing salt additions until one reaches a critical concentration, which characterizes the onset of system destabilization. The concept of an electrical double layer, as it applies to reverse micelles, is considered for explaining features of destabilization, including the initial decrease in reverse micelle size, the destabilization concentration, and the effect of cation valence. We propose that the reduction in size prior to instability is caused by compression of the reverse micelle electrical double layers, as higher concentrations of salts are present. The reduced thickness of the electrical double layers allows the decaying potentials to move into closer proximity to each other before generating enough repulsion to balance the forces for reverse micelle formation and form a new equilibrium average reverse micelle size. The point of reverse micelle instability has been related to the formation of a two-phase system as a result of the inability to further compress the salt co-ions in the core of the reverse micelles, which would cause an excessive repulsive force between the overlapping potentials. We have extracted a critical potential of -89 nV between the two overlapping potentials for the AOT/water/isooctane (ω(0) = 10) systems studied. All these effects have important implications for the preparation of nanopowders by reverse micelle synthesis. If the reverse micelles are unstable before the precipitates are formed, then the advantage of reverse micelle synthesis is immediately lost.

Electric double layers interactions under condition of variable dielectric permittivity

In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer potential, its gradient and the disjoining pressure as well as the effect of variation of dielectric permittivity on these parameters. It has been assumed that plates are separated by a specific distance and contain a liquid solution in between. It is shown that reduction of the dielectric permittivity near the interfaces results in compression of electric double layers and affects the potential and its gradient which leads to a decreased electrostatic repulsion. In addition, it is shown that variation of dielectric permittivity in the case of higher electrolyte concentration, leads to a greater change in potential distribution between two plates.

Influence of (bi)carbonate on bacterial interaction with quartz and metal oxide-coated surfaces

This study investigated the influence of (bi)carbonate on the adhesion of bacteria ( Bacillus subtilis ATCC 6633) to quartz, aluminum oxide-coated, and iron oxide-coated surfaces. Column experiments were conducted at various NaHCO 3 concentrations. Bacterial breakthrough curves were obtained by monitoring effluent, and mass recoveries were quantified from these curves. With NaHCO 3 concentrations varying from 0 to 200 mM, the corresponding effective ionic strength varied from 0 to 149.0 mM and solution pH from 6.2 to 8.7. Results show that at low and intermediate NaHCO 3 concentrations (1 and 10 mM), bacterial adhesion to negatively charged quartz sand increased with increasing NaHCO 3 concentration, due to compression of the electrical double layers. At high NaHCO 3 concentrations (100 and 200 mM), however, bacterial attachment to quartz sand decreased compared to the case of 10 mM, possibly due to formation of short-range forces (steric repulsion/hydration force) by high ionic strength. In aluminum-coated sand, bacterial adhesion decreased gradually with increasing NaHCO 3 concentrations, due to charge modification from positive to negative by adsorbed (bi)carbonate ions. At low concentrations of 0.1 and 1 mM, bacterial attachment to iron-coated sand surfaces decreased with increasing NaHCO 3 concentration, due to charge modification of coated sand surfaces from positive to negative. At intermediate concentration of 10 mM, iron-coated sand surfaces were negatively charged like quartz sand, and so the presence of (bi)carbonate ions resulted in the increment of bacterial adhesion due to compression of the electrical double layers. At high concentrations of 100 and 200 mM (pH 8.5–8.6), where iron-coated surfaces were negatively charged, bacterial deposition decreased compared to the case of 10 mM, possibly due to the same phenomenon observed in quartz sand (short-range forces). This study demonstrates that bacterial adhesions to quartz and metal oxide-coated surfaces in the presence of (bi)carbonate ions show different responses depending on the NaHCO 3 concentration and surface charges of porous media.

Properties of water at hydrophobic surfaces and their impact on wedging pressure

A hypothesis on the impact of water density at hydrophobic surfaces on the electrostatic component of their interaction is proposed. A theoretical model of the double electric layer and wedging pressure at variable density and consequently water permittivity has been developed. It was shown that reduction of permittivity at interphase surfaces determined by their hydrophobicity results in the compression of double electric layers and the weakening of the interaction of the latter.

Electric double layer and electrostatic interaction of hydrophobic particles

An hypothesis regarding the impact of water density near hydrophobic surfaces on the electrostatic component of their interaction was offered. A theoretical model of the electric double layer and the interparticle interaction under conditions of the variable density and, consequently, variable dielectric permittivity of water has been developed. It was shown that reduction of the dielectric permittivity near interfaces determined by their hydrophobicity resulted in compression of double electrical layers and weakening of their overlapping. This, in its turn, results in reduction of the electrostatic repulsion of hydrophobic disperse particles as compared with nonhydrophobic ones.

Role of cation demixing and quasicrystal formation and breakup on the stability of smectitic colloids

The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory has been extensively used to explain colloid stability. This study investigated the effect of demixing of monovalent and divalent cations and crystalline swelling on the breakup and formation of smectite quasicrystals (QCs) and how these processes affect flocculation and dispersion of natural soil clay–humic complexes. The results indicated that in a Ca-dominated system the formation of large QCs enhanced flocculation and that increasing the concentration of Na +, K +, or NH 4 + resulted in the breakup of large Ca-QCs, which enhanced dispersion. In low ionic strength systems, dispersion was caused by expanded double layers (DLVO) and the formation of small QCs. X-ray diffraction analyses showed that as large Ca-QCs breakup, monovalent cations resided primarily on the external surfaces and Ca 2+ was preferentially retained in the interlayers. In high ionic strength systems increasing concentrations of monovalent cations also decreased the size of QCs but the effect was partially counteracted by compression of double layers between QCs. X-ray diffraction analyses indicated that monovalent cations were sorbed on both the external surfaces and in the interlayers in high ionic strength systems.

Study of colloidal stability of allophane dispersion by dynamic light scattering

The aggregation kinetics of the aqueous dispersion of allophane was measured by dynamic light scattering as functions of pH and ionic strength. The sample was purified from natural Kanuma soil (Tochigi, Japan). A notable feature is that the dispersion is composed of aggregated flocs of allophane particles. The experiments were performed adjusting the initial floc diameter by centrifugation. The aggregation was induced by charge neutralization or compression of the electrical double layers, by merely mixing the suspension with an electrolyte solution of controlled pH and ionic strength. After the initial mixing operation, the suspension was placed in a static condition and the temporal variation of the average hydrodynamic diameter was monitored in situ . In the initial stage, the diameter dramatically increased reflecting the aggregation induced by the hydrodynamic mixing. Due to the Brownian aggregation, this initial enhancement was followed by a moderate increase. Under the Brownian aggregation, the aggregation rates were found to take a certain limiting value denoting fast coagulation irrespective of charge neutralization or compression of the electric double layers. When the salt concentration is not sufficiently high, the rate of aggregation against pH gradually increases and approaches the fast-coagulation domain; however, the rate decreases rather rapidly as the pH increases. This behavior was interpreted considering pH-dependent charge distribution generated on the surface of allophane particles with peculiar morphology. This interpretation was supported by electrophoretic mobility data. In contrast with the Brownian aggregation, the rate of orthokinetic aggregation induced by charge neutralization was detected to be slightly faster than that induced by compression of the electric double layers.

The Destructive Role of Diffusion on Clay Membrane Behavior

AbstractThe results of a combined chemico-osmotic/diffusion experiment conducted on a geosynthetic clay liner (GCL) containing Na-bentonite illustrate the destructive role of diffusion on the ability of the GCL to act as a semipermeable membrane. The experiment is conducted by maintaining a concentration difference of 5 mM CaCl2 across the GCL specimen while preventing the flow of solution through the specimen. A time-dependent membrane efficiency is derived from measured pressure differences induced across the specimen in response to the applied concentration difference. The diffusive mass fluxes of the solutes (Cl− and Ca2+) through the specimen are also measured simultaneously. An initial increase in induced pressure difference across the specimen to a peak value of 19.3 kPa is observed, followed by a gradual decrease to zero. The decrease in induced pressure difference is consistent with compression of diffuse double layers between clay particles and particle clusters due to diffusion of Ca2+, resulting in a concomitant increase in pore sizes and decrease in the observed membrane behavior. The time required for effective destruction of the initially observed semipermeable membrane behavior correlates well with the time required to achieve steady-state Ca2+ diffusion. The results have important implications for the ability of clays to sustain membrane behavior.

Chemico-Osmotic Efficiency of a Geosynthetic Clay Liner

Chemico-osmotic efficiency coefficients, ω, are determined from measured differential pressures across specimens of a geosynthetic clay liner (GCL) containing granular bentonite in response to applied differences in potassium chloride (KCl) concentrations under no-flow conditions. The results show that the GCL acts as a semipermeable membrane with ω values at steady state, ωss, ranging from 0.08 to 0.69 for KCl concentration differences ranging from 0.0039 to 0.047 M. The chemico-osmotic efficiency of the GCL decreases with increasing porosity and increasing KCl concentration. The decrease in ωss with increasing porosity is consistent with an increase in pore size reflected by an increase in measured hydraulic conductivity. The decrease in ωss with increasing KCl concentration is consistent with compression of the diffuse double layers surrounding the clay particles, and is reflected by a time-dependent decrease in the induced differential pressure as well as an increase in the hydraulic conductivity of t...

Sorption of tannic acid on zirconium pillared clay

AbstractZirconium pillared clay (PILC) was prepared using montmorillonite as the base clay. Adsorption of tannic acid (tannin) was studied by a batch equilibrium technique, as a function of adsorbate concentration, temperature, pH, agitation speed, particle size of the adsorbent and ionic strength. The process of uptake is governed by diffusion controlled first‐order reversible rate kinetics. The higher uptake for the pH range 4.0–6.0 was attributed to external hydrogen bonding between phenolic‐OH groups of tannin molecules and the hydrogen bonding sites on the clay. The removal of tannin by adsorption was found to be >99.0% depending on the initial concentration in the pH range of 4.0–6.0. The process involves both film and pore diffusion to different extents. The effects of solute concentration, temperature, agitation speed and particle size on the diffusion rate were investigated. Tannin uptake was found to increase with ionic strength due to the compression of diffuse double layers. The applicability of Langmuir and Freundlich isotherm models has been tested. The maximum adsorption capacity of PILC was found to be 45.8 µmol g−1 of clay and the affinity constant is 2.9 × 10−2 dm3 µmol−1 at 30 °C. Thermodynamic parameters such as ΔG °,ΔH ° and ΔS ° were calculated to predict the nature of adsorption. The isosteric enthalpies of adsorption were also determined and found to decrease with increasing surface coverage. Regeneration with hot water (60 °C) has been investigated for several cycles with a view to recovering the adsorbed tannin and also restoring the sorbent to its original state.Copyright © 2001 Society of Chemical Industry

Stability of ground and precipitated CaCO 3 suspensions in the presence of polyethylene oxide and kraft lignin

The behavior of two commercial types of ground and precipitated CaCO 3 pigments differ because of different surface characteristics. Ground CaCO 3 is treated with a dispersant and, in the absence of salt, it forms a stable suspension because of electrical double layer repulsion. Its stability and surface charge are not affected by polyethylene oxide or sulfonated kraft lignin, added separately or in combination. Destabilization takes place in the presence of a sufficient amount of salt owing to the compression of double layers. However in a narrow region of salt concentration the polyethylene oxide improves stability by an electrosterical effect. In contrast, precipitated CaCO 3 aggregates at fast rates, even in the absence of salt, because of insufficient double layer repulsion. Its behavior is not affected by polyethylene oxide addition, but the presence of kraft lignin results in stabilizing the suspension by adsorbing on CaCO 3 particles, thus increasing the negative surface charge and, consequently, the electrostatic repulsion.

The formation of humic coatings on mineral particles under simulated estuarine conditions—A mechanistic study

The adsorption of three humic substances isolated from the River Dodder (Eire) and one commercial humic acid (Aldrich) by six minerals was studied and found to be influenced by mineral type, the nature of the humics and by the solution characteristics. Adsorption was heavily pH-dependent, with lower uptake at higher pH values due to increased ionization of the humic substances. The amount of humic substances adsorbed was in the order: Aldrich humic acid > Dodder humic acid > Dodder fulvic acid > Dodder hydrophilic macromolecular acid corresponding to a decreasing aromatic carbon content and increasing O/C ratio. Desorption experiments showed Aldrich humic acid was the most difficult to be desorbed, followed by Dodder humic acid, Dodder fulvic acid then Dodder hydrophilic macromolecular acid. Humic uptake was found to increase with ionic strength due to the neutralization of charges on both mineral surfaces and humic substances, and more importantly, the compression of diffuse double layers; this also showed that van der Waals attraction is an important part of the interactive forces between humic substances and mineral particles. The amount of humic substances adsorbed varied with mineral type, particle size and surface area, with aluminium oxide having the highest capacity. The effect of temperature on humic adsorption was shown to vary with humic type and two types of reaction mechanism have been proposed responsible for the humic-clay interactions.

Acoustic microscopy improves internal reliability of IC packaging : Thomas E. Adams. Semiconductor Int. 100 (February 1985)

The aggregation kinetics of the aqueous dispersion of allophane was measured by dynamic light scattering as functions of pH and ionic strength. The sample was purified from natural Kanuma soil (Tochigi, Japan). A notable feature is that the dispersion is composed of aggregated flocs of allophane particles. The experiments were performed adjusting the initial floc diameter by centrifugation. The aggregation was induced by charge neutralization or compression of the electrical double layers, by merely mixing the suspension with an electrolyte solution of controlled pH and ionic strength. After the initial mixing operation, the suspension was placed in a static condition and the temporal variation of the average hydrodynamic diameter was monitored in situ. In the initial stage, the diameter dramatically increased reflecting the aggregation induced by the hydrodynamic mixing. Due to the Brownian aggregation, this initial enhancement was followed by a moderate increase. Under the Brownian aggregation, the aggregation rates were found to take a certain limiting value denoting fast coagulation irrespective of charge neutralization or compression of the electric double layers. When the salt concentration is not sufficiently high, the rate of aggregation against pH gradually increases and approaches the fast-coagulation domain; however, the rate decreases rather rapidly as the pH increases. This behavior was interpreted considering pH-dependent charge distribution generated on the surface of allophane particles with peculiar morphology. This interpretation was supported by electrophoretic mobility data. In contrast with the Brownian aggregation, the rate of orthokinetic aggregation induced by charge neutralization was detected to be slightly faster than that induced by compression of the electric double layers.