Cation Binding Predictions of Surface Complexation Models: Effects of pH, Ionic Strength, Cation Loading, Surface Complex, and Model Fit

Robertson, A.; Leckie, James O.

doi:10.1006/jcis.1996.4752

Cited by 95 publications

(70 citation statements)

References 43 publications

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“…However, the presence of coions in the β-plane in the absence of positively-charged surface functional groups contradicts the TLM and most other EDL models (a notable exception being the modified TLM of Robertson and Leckie [15]), but agrees with the results of all-atom theoretical calculations [98]. We hypothesize that the few Cl -OSSCs observed in our simulations may in fact be stabilized as positively-charged ion pairs, CaCl + .…”

Section: Coion Exclusionsupporting

confidence: 80%

“…By analogy with planar capacitors, these parameters are sometimes modeled with the relation [4,32]: Yates et al [3] using the unsupported assumption that ψ d is equal to the electrokinetic "zeta" potential [16,31]) and fitting C 1 to proton and electrolyte adsorption data using the TLM; this method yields C 1 = 0.6 to 2.2 for a range of electrolytes and mineral surfaces [15,[31][32][33]104,125]. Other studies have assumed that C 2 = ∞ (i.e., ψβ = ψ d [107]) or C 2 = C 1 [7,126], or have fitted both C 1 and C 2 [105,107].…”

Section: Implications For Modeling Mineral-water Interfacial Propertiesmentioning

confidence: 99%

“…This view is adopted, for example, as the molecular basis for the widely-applied triple-layer model (TLM [3][4][5]), on which the distribution of ions near a charged planar solid surface is calculated under a set of simplifying assumptions that include assigning all ISSCs to a plane at the solid surface (0-plane), all OSSCs to a second plane lying farther into the aqueous phase (β-plane), and all DS species to a region lying beyond a third plane farther out than the β-plane (d-plane) ( Inferences about EDL surface speciation and molecular structure from experimental data on proton and ion adsorption [6,7,8], salt filtration efficiency [9], second harmonic generation [10], electrophoretic mobility [11], or interparticle forces [12] are necessarily sensitive to simplifying EDL model assumptions such as those just described for the TLM [13][14][15][16]. Models of the EDL that approximate liquid water as a uniform dielectric continuum (such as the Poisson-Boltzmann equation [17,18], hypernetted chain theory [19,20], or the primitive model [18,21]) inherently cannot describe surface complexes [17,18].…”

Section: Introductionmentioning

confidence: 99%

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Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Bourg

Sposito

2011

Journal of Colloid and Interface Science

257

224

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We report new molecular dynamics results elucidating the structure of the electrical double layer (EDL) on smectite surfaces contacting mixed NaCl-CaCl 2 electrolyte solutions in the range of concentrations relevant to pore waters in geologic repositories for CO 2 or high-level radioactive waste (0.34 to 1.83 mol c dm -3 ). Our results confirm the existence of three distinct ion adsorption planes (0-, β-, and d-planes), often assumed in EDL models, but with two important qualifications: (1) the location of the β-and dplanes are independent of ionic strength or ion type and (2) "indifferent electrolyte" ions can occupy all three planes. Charge inversion occurred in the diffuse ion swarm because of the affinity of the clay surface for CaCl + ion pairs. Therefore, at concentrations ≥ 0.34 mol c dm -3 , properties arising from long-range electrostatics at interfaces (electrophoresis, electro-osmosis, co-ion exclusion, colloidal aggregation) will not be correctly predicted by most EDL models. Co-ion exclusion, typically neglected by surface speciation models, balanced a large part of the clay mineral structural charge in the more concentrated solutions. Water molecules and ions diffused relatively rapidly even in the first statistical water monolayer, contradicting reports of rigid "ice-like" structures for water on clay mineral surfaces.

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Section: Coion Exclusionsupporting

confidence: 80%

Section: Implications For Modeling Mineral-water Interfacial Propertiesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Bourg

Sposito

2011

Journal of Colloid and Interface Science

257

224

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“…Robertson and Leckie (1996) systematically examined the effects of SCM model choice on cation binding predictions when pH, ionic strength, cation loading and proposed surface complex stoichiometry were varied. They show that although different models can be used to obtain comparable fits to the same experimental data set, the stoichiometry of the proposed surface complex will vary considerably between the models.…”

Section: Constantsmentioning

confidence: 99%

Environmental Geochemistry of Radioactive Contamination

Siegel

Bryan

2003

Treatise on Geochemistry

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This report attempts to describe the geochemical foundations of the behavior of radionuclides in the environment. The information is obtained and applied in three interacting spheres of inquiry and analysis: 1) experimental studies and theoretical calculations, 2) field studies of contaminated and natural analog sites and 3) model predictions of radionuclide behavior in remediation and waste disposal. Analyses of the risks from radioactive contamination require estimation of the rates of release and dispersion of the radionuclides through potential exposure pathways. These processes are controlled by solubility, speciation, sorption, and colloidal transport, which are strong functions of the compositions of the groundwater and geomedia as well as the atomic structure of the radionuclides.The chemistry of the fission products is relatively simple compared to the actinides. Because of their relatively short half-lives, fission products account for a large fraction of the radioactivity in nuclear waste for the first several hundred years but do not represent a long-term hazard in the environment. The chemistry of the longer-lived actinides is complex; however, some trends in their behavior can be described. Actinide elements of a given oxidation state have either similar or systematically varying chemical properties due to similarities in ionic size, coordination number, valence, and electron structure. In dilute aqueous systems at neutral to basic pH, the dominant actinide species are hydroxy-and carbonato-complexes, and the solubility-limiting solid phases are commonly oxides, hydroxides or carbonates. In general, actinide sorption will decrease in the presence of ligands that complex with the radionuclide; sorption of the (IV) species of actinides (Np, Pu, U) is generally greater than of the (V) species.The geochemistry of key radionuclides in three different environments is described in this report. These include: 1) low ionic strength reducing waters from crystalline rocks at nuclear waste research 4 sites in Sweden; 2) oxic water from the J-13 well at Yucca Mountain, Nevada, the site of a proposed repository for high level nuclear waste (HLW) in tuffaceous rocks; and 3) reference brines associated with the Waste Isolation Pilot Plant (WIPP). The transport behaviors of radionuclides associated with the Chernobyl reactor accident and the Oklo Natural Reactor are described. These examples span wide temporal and spatial scales and include the rapid geochemical and physical processes important to nuclear reactor accidents or industrial discharges as well as the slower processes important to the geologic disposal of nuclear waste.Application of geochemical information to remediating or assessing the risk posed by radioactive contamination is the final subject of this report. After radioactive source terms have been removed, large volumes of soil and water with low but potentially hazardous levels of contamination may remain. For poorly-sorbing radionuclides, capture of contaminated water and removal of radi...

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“…It can explain the adsorption of ions in aqueous solution on solid surfaces phenomenon, since its nature is more chemical than physical. The model proved to be applicable for various adsorption systems 3,4,5,6 . Modeling of noble metal complex ions adsorbed onto single oxides has been given more attention than composite oxides, although the latter are used in many industries.…”

Section: Introductionmentioning

confidence: 98%

Untitled

Therdthianwong¹,

Tongsima²,

Therdthianwong³

2004

ScienceAsia

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An adsorption model explaining and predicting the adsorption phenomena of palladium complex ions over MgO/Al 2 O 3 and CuO/Al 2 O 3 was developed based on the triple layer theory. Wet impregnation or adsorption experiments were conducted to determine the solution variables and some parameters used in the model and to verify the adsorption model. Adsorption of palladium complex ions on pure oxides (Al 2 O 3 , MgO and CuO) and composite oxides (3% and 15% of MgO and CuO on Al 2 O 3 ) was investigated at different solution pH. From the experiments, Pd adsorption capability of pure and composite oxides was influenced by solution pH, type of promoter on the support and concentration of promoter. Overall the results predicted from the triple layer model agreed reasonably well with the experimental data, except in the pH range near the point of zero charge of oxide. The suggested pH value for preparing Pd/MgO/Al 2 O 3 and Pd/ CuO/Al 2 O 3 composite oxides is the pH close to the initial pH of the palladium precursor solution.

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Cation Binding Predictions of Surface Complexation Models: Effects of pH, Ionic Strength, Cation Loading, Surface Complex, and Model Fit

Cited by 95 publications

References 43 publications

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions

Environmental Geochemistry of Radioactive Contamination

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