Immobile Solid Phase Research Articles

Dynamic Self-Repairing Hybrid Liquid-in-Solid Protective Barrier for Cementitious Materials.

Corrosion and surface fouling of structural materials, such as concrete, are persistent problems accelerating undesirable material degradation for many industries and infrastructures. To counteract these detrimental effects, protective coatings are frequently applied, but these solid-based coatings can degrade or become mechanically damaged over time. Such irreversible and irreparable damage on solid-based protective coatings expose underlying surfaces and bulk materials to adverse environmental stresses leading to subsequent fouling and degradation. We introduce a new concept of a hybrid liquid-in-solid protective barrier (LIB) to overcome the limitations of traditional protective coatings with broad applicability to structural materials. Through optimization of capillary forces and reduction of the interfacial energy between an upper mobile liquid and a lower immobile solid phase, a stable liquid-based protective layer is created. This provides a persistent self-repairing barrier against the infiltration of moisture and salt, in addition to omniphobic surface properties. As a model experimental test bed, we applied this concept to cementitious materials, which are commonly used as binders in concrete, and investigated how the mobile liquid phase embedded within a porous solid support contributes to the material's barrier protection and antifouling properties. Using industry standard test methods for acid resistance, chloride-ion penetrability, freeze-thaw cyclability, and mechanical durability, we demonstrate that LIBs exhibit significantly reduced water absorption and ion penetrability, improved repellency against various nonaqueous liquids, and resistance to corrosion while maintaining their required mechanical performance as structural materials.

Dynamic modelling of injectivity evolution in unconsolidated sands

Fluid injection into unconsolidated formations serves many different purposes in the oil and gas industry. EOR projects require fluid injection at sustained high flow rates into the reservoir for years. Depending on the matrix properties and injection conditions, individual grains may be detached from the sand matrix and carried away by the fluid. During well shut-ins, pressure transients are generated and the direction of the flow is reversed allowing the grains to be transported and deposited near and even inside the wellbore. The deposited grains may plug the pores around the wellbore and decrease the injectivity, a phenomenon often observed at injection wells targeting unconsolidated formations. In order to address this issue, we implement a model consisting of partial differential equations solved through the numerical finite element methods that decomposes the porosity into mobile and immobile solid phases plus the liquid phase. The mass exchange from mobile to immobile solid phases is dependent on the deposition and erosion rates that are a function of the pressure gradient and stress concentrations around the wellbore. The system uses appropriate scales in size and time as well as appropriate field parameters. The results show how the porosity evolves over time around a hypothetical wellbore; the erosion reduces the pressure gradient until the erosion is negligible. The injection rate, the initial porosity heterogeneity and inter-grain forces (degree of consolidation) proved to have a significant impact on the matrix erosion. Simulations that emulate the effect having gravel and frac-packs were also performed evidencing that the different completion systems help to reduce the formation of high porosity channels around the wellbore during fluid injection.

Coupled effect of extended DLVO and capillary interactions on the retention and transport of colloids through unsaturated porous media

Colloids are potential vectors of contaminants in the subsurface environment. The knowledge of transport and retention behaviors of colloids is of primary importance for assessment and prediction of subsurface pollution risks. In this study, sand column experiments were conducted to investigate the coupled effects of various interfacial forces on the retention and transport of a hydrophilic silica colloid and a relatively hydrophobic latex colloid. Water column experiments were performed to observe the movement of colloids with air bubbles. Extended DLVO interaction energies and capillary potential energy were calculated to analyze colloid retention at air-water interface (AWI), solid-water interface (SWI), and air-water-solid interface (AWS). Results show that colloid retention decreases due to increase in electrostatic repulsion and Born repulsion as well as decrease in Lewis acid-base attraction and hydrophobic interactions. Water content effect and hydrophobic effect on colloid retention become more predominant in the solution of higher ionic strength. Colloid retention at AWI is minimal (i.e., due to nonexistence of primary and secondary minima) at the ionic strengths <75mM. Capillary potential energy (107–108 KBT) of colloids is 4–5 orders of magnitude greater than the extended DLVO interaction energy (~103 KBT), suggesting that capillary retention at AWS is the primary mechanism controlling colloid retention in unsaturated porous media. Results from this study show that immobile solid phase (e.g., soil) could be much more important than air phase in determining colloid retention in unsaturated porous media under unfavorable conditions, especially in the solutions of high ionic strengths.

Computer modeling of column apparatuses: 2. Multistep modeling approach

A new approach for computer modeling of the mass transfer processes in column apparatuses, on the base of the convection-diffusion type of models in the physical approximations of the mechanics of continua, is proposed. In the cases of a nonstationary chemical adsorption in gas-solid systems, the presence of mobile (gas) and immobile (solid) phases in the conditions of long-time processes, leads to the nonstationary process in the immobile phase and stationary process in the mobile phase, practically. As a result, different coordinate systems must be used in the gas and solid phase models. A combination of a multistep algorithms and MATLAB are used for the solutions of the equations set in different coordinate systems. As a result, it is shown that the experimental data, obtained from the column with real radius and small height, are useful for parameters identifications in the average concentration-type models.

Arsenic Content and the Bioavailability in Farmland Soils Affected by Mining Activities of a Realgar Ore, South China

Investigation on arsenic (As) accumulation in soil and agricultural products collected from the areas influenced by mine tailings and spoils around Shimen realgar mine, Hunan province, China, was carried out in this study. Water solubility, fractionation and bioavailability of As were determined as well to understand the environmental risk of arsenic releasing from farmland to water system this region. The results indicated that total soil arsenic concentrations varied from 18.9 to 932mg kg-1 and the highest arsenic concentration exceeding 500mg kg-1 in soils occurred only within 500m from these arsenic sources, and relatively low content (&lt;40 mg="" kg="" sup=""&gt;-1) appeared in the areas far away (&gt;3000m) from the pollution source. Arsenic content in dryland soils decreased with the distance from the mining arsenic ore, tailings and heaps increased. Through sequential extraction procedure (SEP), it was verified that the least arsenic amount occurred for exchangeable fraction with the percentage of 1.1%, then the organically bound fraction (1.6%), and much of the arsenic in the soils was associated with relatively immobile solid phases as residual fraction ranging from 87.5% to 93.3%. The fraction of mobile species, which potentially is harmful to the environment, was found to be higher in the soils with more AsT (total arsenic) content. Through statistical analysis, it was found out that arsenic content in plants was significantly correlated (R2=0.202; P&lt;0.01) with exchangeable As among these five As fractions in soils. Comparing extracted arsenic content in soils using distilled water (H2O-As), muriatic acid (HCl-As) and ammonium chloride (NH4Cl-As), better positive relationship occurred significantly (R2=0.226; P&lt;0.01) between NH4Cl-As and arsenic in plant, indicating the bioavailability was most closely related to NH4Cl-As rather than total As and other chemical solvents for extracting arsenic from soil.

Diagramas de Estabilidad Multifases Modificados: Un caso de AMD en Northumberland, UK

The weathering of sulphide minerals within spoil heaps causes the release of sulphate and environmentally hazardous metal ions. Newly-formed species can subsequently precipitate as highly soluble, secondary sulphate minerals, which, in turn, might be flushed by dilute recharge water or eventually transformed into more stable minerals. These processes determine which components are retained in the spoil as immobile solid phases and which (and when) others are released into the wider aquatic environment. To elucidate this sequence of mineral formation and transformation, we studied mineral-fluid equilibria in a major abandoned coal mine spoil heap at the former Shillbottle Colliery, Northumberland, UK. The investigations focussed on stability of iron minerals produced during the acid mine drainage process. The multi-component Phreeplot-calculated pE/pH diagrams reveal that many post-mining secondary minerals may co-exist, in contrast to what is indicated by the more commonly used charts. Being able to visualize the mutual stability of these minerals under specific chemical and physical conditions might aid understanding of formation and transformation mechanisms.

Mathematical modeling of the lysis of clots in blood vessels

A mathematical model of the lysis of clots in blood vessels has been constructed on the basis of convectiondiffusion equations. The fibrin clot is considered as an immobile solid phase, and the plasminogen, plasmin, and plasminogen activators — as dissolved liquid phases. As a result of the numerical solution of the model, dependences predicting the development of the lysis process have been obtained. An important role of clot swelling in the process of lysis has been revealed.

Effect of colloids on transfer of radionuclides by subsurface water

The fluid transfer of radionuclides in the geologic medium is considered under conditions when radionuclides are contained in fluids not only as solutes but also as colloids. The effect of colloidal transport of radionuclides on the rate of spreading of radioactive contamination in an underground medium is estimated, with assessment of this effect in mathematical models describing the transport of radionuclides by subsurface water. For this purpose, the exchange of radionuclides between subsurface water, colloid, and an immobile solid phase is considered, taking into account the precipitation of colloidal particles on both the immobile solid phase and other colloidal particles and their recurrent mobilization into the liquid phase. It is noted that, in real colloidal transfer, the heterogeneity of the geologic medium and colloidal particles in subsurface water is of great importance. The known models of colloidal transfer of radionuclides are evaluated on the basis of the analysis performed.

Arsenic in the soils of Zimapán, Mexico

Arsenic concentrations of 73 soil samples collected in the semi-arid Zimapán Valley range from 4 to 14 700 mg As kg −1. Soil arsenic concentrations decrease with distance from mines and tailings and slag heaps and exceed 400 mg kg −1 only within 500 m of these arsenic sources. Soil arsenic concentrations correlate positively with Cu, Pb, and Zn concentrations, suggesting a strong association with ore minerals known to exist in the region. Some As was associated with Fe and Mn oxyhydroxides, this association is less for contaminated than for uncontaminated samples. Very little As was found in the mobile water-soluble or exchangeable fractions. The soils are not arsenic contaminated at depths greater than 100 cm below the surface. Although much of the arsenic in the soils is associated with relatively immobile solid phases, this represents a long-term source of arsenic to the environment.

Influence of dissolved and colloidal phase humic substances on the transport of hydrophobic organic contaminants in soils

Dissolved and colloidal size organic matter (DOM) controls the mobility of hydrophobic organic chemicals (HOC) in soils by affecting the sorptive interaction between the soil matrix and the solution phase. The association between HOC and DOM in the soil solution leads to an increase in the water solubility of HOC. DOM is a reactive component of the soil solution with respect to the immobile solid phase. Therefore the overall mobility of HOC in soils is enhanced due to co-transport with DOM as the mobile carrier or reduced due to co-sorption or cumulative sorption. The specific processes relevant to the DOM-mediated fate of HOC in natural and contaminated soils are discussed, with special consideration to the effect of (i) soil physico-chemical parameters (ionic strength, composition, pH), (ii) DOM of different origin, and (iii) aging of a contamination on HOC release.

A DISCRETE BLOB MODEL OF CONTAMINANT TRANSPORT IN GROUNDWATER WITH TRAPPED NON-AQUEOUS PHASE LIQUIDS

The present work describes a model developed for multiphase transport in the subsurface. The system under consideration comprises three phases including the immobile solid phase composed of soil grains, the aqueous phase flowing through the bed of soil grains, and the non-aqueous phase of liquids (NAPLs) that may consist of several mutually soluble compounds. Numerous field data and experimental results have indicated that the residual nonwelting fluids of the NAPLs in groundwater systems are trapped, i.e., completely surrounded by the wetting aqueous phase. In the model, therefore, the NAPLs are treated as discrete blobs with generalized local-size distribution, while the aqueous phase is assumed To be a continuum. In addition, the model takes into account the surface area-to-volume ratio and the ratio of the aqueous contacting area to the overall surface area of NAPL blobs. Interactions between the two liquid phases manifest themselves in the governing equations of the aqueous phase as an integral over ...

Reactive Solute Transport in Streams: 1. Development of an Equilibrium‐Based Model

An equilibrium‐based solute transport model is developed for the simulation of trace metal fate and transport in streams. The model is formed by coupling a solute transport model with a chemical equilibrium submodel based on MINTEQ. The solute transport model considers the physical processes of advection, dispersion, lateral inflow, and transient storage, while the equilibrium submodel considers the speciation and complexation of aqueous species, precipitation/dissolution and sorption. Within the model, reactions in the water column may result in the formation of solid phases (precipitates and sorbed species) that are subject to downstream transport and settling processes. Solid phases on the streambed may also interact with the water column through dissolution and sorption/desorption reactions. Consideration of both mobile (water‐borne) and immobile (streambed) solid phases requires a unique set of governing differential equations and solution techniques that are developed herein. The partial differential equations describing physical transport and the algebraic equations describing chemical equilibria are coupled using the sequential iteration approach.

Mathematical Aspects of the Combustion of a Solid by a Distributed Isothermal Gas Reaction

When a diffusing gas reacts isothermally with an immobile solid phase, the resulting equations form a semilinear system consisting of a parabolic partial differential equation for the gas concentration coupled with an ordinary differential equation for the solid concentration. Existence and uniqueness proofs are given which include the important case of nonlipschitzian reaction rates such as those of fractional-power type. Various qualitative features of the solution are studied: approach to the steady state; monotonicity in time; and dependence on initial conditions, on the porosity, and on the geometry. The relationship between the original problem and the pseudo-steady-state approximation of zero porosity is investigated. When the solid reaction rate is nonlipschitzian, there is a conversion front separating a fully converted region adjacent to the boundary and a partially converted interior core. Estimates are given for the time to full conversion. If the gas reaction rate is nonlipschitzian the gas may not at first fully penetrate the solid. Estimates are given for the time at which full penetration occurs.

Traveling Waves for Distributed Gas-Solid Reactions

We investigate traveling waves for distributed gas-solid reactions with a powerlaw reaction rate. In this model the diffusing gas reacts with an immobile solid phase, leading to coupled partial and ordinary differential equations. We consider both the case of positive porosity and the pseudo-steady-problem with zero porosity. The wave profile consists of a pair ( u, w) where u is the gas concentration and w is the solid concentration. As boundary conditions we take w(− ∞) = 0, u(+ ∞) = 0, w(+ ∞) = 1, as is appropriate for a wave traveling from left to right while consuming the solid as it moves. Our principal result, obtained by phase-plane methods, is that to each velocity v > 0 there corresponds a unique wave profile, modulo translations. If the power of the solid reaction rate is less than 1, a conversion front exists behind which the solid is fully consumed ( w ≡ 0); if the power of the gas reaction rate is less than 1, the gas does not fully penetrate the solid, leading to a penetration front ahead of which u ≡ 0. We provide estimates for the location of these fronts and analyze their local behavior. Our results both agree with and extend those of Bobisud who studies similar equations in a different context and on a semi-infinite interval.

Comparison of Models for Describing the Transport of Dissolved Organic Carbon in Aquifer Columns

AbstractDissolved organic carbon (DOC) is a reactive constituent in aquifer and soil media and equilibrates between the mobile aqueous phase and the immobile solid phase. Since DOC is believed to accelerate the transport of associated contaminants, yet is known to interact with aquifer and soil material, our objective was to define and model those processes governing DOC adsorption to porous media that may affect the cotransport of contaminants. Column displacement experiments of DOC through aquifer sediments were modeled with various formulations of the convective‐dispersive equation, which considered time‐dependent adsorption reactions and linear or nonlinear adsorption processes. Batch equilibrium adsorption isotherm and kinetic studies for DOC interaction with the sediments were used to parameterize the transport models. The equilibrium DOC‐adsorption isotherm was nonlinear and was adequately described by the Langmuir equation. The adsorption of DOC to the aquifer sediment was also time dependent and the batch results could be described by two simultaneous reaction rates for solution concentrations ≥ 10 mg DOC L−1 and a single reaction rate for solution concentrations &lt;10 mg DOC L−1. Observed DOC breakthrough curves (BTCs) with influent concentrations ≥ 10 mg DOC L−1, were adequately modeled as two‐site, non‐linear adsorption processes, with DOC interactions with both types of sites being time dependent. Batch adsorption and kinetic parameters were generally successful in describing DOC transport; however, the magnitude of the initial batch rate coefficient was significantly larger than that observed for the displacement experiments. The extended tailing of the observed DOC BTCs was influenced more by the slow, time‐dependent adsorption of DOC during transport than to the non‐linear features of the adsorption isotherms. Observed DOC BTCs with influent concentrations &lt;10 mg DOC L−1 did not exhibit extensive tailing and were modeled as a one‐site, linear or nonlinear, time‐dependent adsorption process.

Conversion estimates for gas-solid reactions

Many chemical engineering processes involve a reaction between a diffusing substance and an immobile solid phase. The usual treatments are based on the assumptions that either diffusion or reaction dominates. Instead, we shall model an isothermal process in which reaction and diffusion are of the same order as would occur, for instance, in low temperature coke burning. Mass balances then lead to a parabolic system for the concentrations of the two phases. The system can be reduced to a scalar parabolic problem for the cumulative gas concentration. The popular pseudo-steady-state approximation is then obtained by setting the porosity ∈ equal to zero. This pseudo-steady-state problem is an elliptic problem in which time appears only as a parameter in the boundary condition. In previous work, we have shown that the pseudo-steady-state solution provides an O(∈) approximation to the exact concentration, uniformly in space and time. The present paper is concerned with estimates for the conversion, that is, the fraction of solid that has been converted to products by time t. We obtain bounds for the conversion in terms of a similar quantity (explicity calculable in some cases) for the pseudo-steady-state problem.

Validity of the pseudo-steady-state approximation

When a diffusing substance interacts isothermally with an immobile solid phase, the resulting equations form a parabolic system of nonlinear partial differential equations for the nondimensional concentrations of the two phases. Introduction of the cumulative fluid concentration as a new dependent variable reduces the system to a scalar parabolic equation in which a small parameter multiplies the time derivative of the cumulative concentration. Omission of this term yields a pseudo-steady-state elliptic problem in which time appears only as a parameter in the boundary condition. The purpose of the paper is to rigorously justify this commonly used approximation. The major tools needed are suitable versions of the maximum principles for parabolic and elliptic equations.

Production and release of ions in the Fast Atom Bombardment ion source

FAB spectra have been obtained from several organic diammonium salts. The free dication was observed in only one case. Solid samples of the salts did not yield simply interpretable data. Mass spectra of the salts from a glycerol or glycerol/inorganic salt matrix exhibit several cation and anion related peaks as well as numerous singly charged fragment ions corresponding to charge separation, dealkylation, and elimination reactions accompanied by hydrogen transfer. These results point to low energy desorption pathways of preformed ions from immobile solid phases and mobile, concentrated liquid or high pressure gas phases.