Effects of Microbially Induced Carbonate Precipitation on Diffuse Double Layer and Particle Fabric of Oil Sands Fine Tailings

Microbially induced carbonate precipitation (MICP) is a sustainable biological process that catalyzes carbonate mineral precipitation within geomaterials. This study evaluates the performance and mechanisms of the MICP treatment for flocculating the oil sands fine tailings (FT). Column tests showed that the untreated FT did not decant during the 31 days. However, the MICP technique shortened the dewatering process. To elucidate the mechanisms of the MICP-induced flocculation of the FT, the diffuse double layer (DDL) thickness and microstructure of the specimens were evaluated. Three chemical equilibrium scenarios that gradually considered the MICP-biochemical reactions were explored to analyze the change of the DDL thickness. The results showed that increasing of ionic strength by urea hydrolysis decreased the DDL thickness. The fabric observation indicated that the specimens with the most calcium carbonate precipitation had the densest fabric. In summary, the MICP technique densified the fabric of FT via ureolysis process and precipitating minerals.

Insight into Debye Hückel length (κ−1): smart gravimetric and swelling techniques reveals discrepancy of diffuse double layer theory at high ionic concentrations

Smart gravimetric and swelling techniques were utilized in this work to examine the validity of the Debye Hückel length (κ−1) equation when shale interacts with highly concentrated salt solutions. The swelling and shrinkage behavior of two different shales, when exposed to monovalent and divalent ionic solutions (NaCl, KCl and CaCl2) at concentrations ranging from 2 to 22%w/w was observed and measured. Shale swelling and shrinkage results show that Debye Hückel length (κ−1) equation seems to work adequately at low ionic concentrations where osmotic water flow out of shale plays a major role in decreasing the diffuse double layer thickness by withdrawing water out and thereby shrinking κ−1. At high ionic concentration levels, the flow of associated water into the diffuse double layer negates the withdrawal of osmotic water out of the diffuse double layer which could maintain κ−1 or possibly increase it. Data on measured ionic uptake into shale suggests that excessive ionic diffusion into shale, especially at high concentrations, leads to higher electrical repulsion between alike ions in the diffuse layer which could lead to the expansion of the diffuse double layer thickness. Furthermore, swelling and shrinkage data analysis for shale suggests the existence of a ‘critical concentration’ below which the Debye Hückel length equation works. Above the critical concentration, the validity of the Debye Hückel length equation might be in question. The critical concentration is different for all ions and depends on ionic valence, hydrated ion diameter, and clay type.

Surface Complexation Modelling of Potential Determining Ions Sorption on Oil/Brine and Brine/Rock Interfaces

Previous studies on smart water effects have suggested wettability alteration as the most significant mechanism for additional oil recovery during smart water injection. Though many other mechanisms have been observed and proposed in several other studies, much more attention is paid to the detachment of oil films from rock surfaces. It is, however, clear from prevailing understanding that the activities at oil/brine interfaces might require as much attention as given to the brine/rock interfaces. This paper presents diffuse double layer surface complexation modelling of the adsorption of potential determining (Ca2+, Mg2+ and SO42-) ions on oil carboxylic and carbonate surfaces. Surface complexation models are developed by defining the adsorption sites, surface area and mass of the oil and carbonate surfaces. The chemical reactions involving the surface sites and five different brine solutions are also defined. The brine solutions include formation water, sea water, sea water diluted 20 and 50 times, and sea water with four times SO42- concentration. The amount of the divalent ions adsorbed at pH range of 5 to 8 are determined after the reactions had reached equilibrium. Adsorption of the ions on oil carboxylic and carbonate surfaces at elevated temperature for the sea water is also investigated. Results show that significant number of divalent ions are collected at the oil/brine interfaces just as adsorbed at the brine/rock interfaces. The results suggest that the equilibrium reactions and the dynamics at the two mathematical interfaces in any oil/brine/rock systems are equally important to reach a full understanding of the main mechanisms behind smart water effects. Therefore, the dynamics of ionic reactions at the oil/brine interface can play critical roles in defining smart water effects on residual oil mobilization.

Differentiation of SCC Susceptibility with EIS of Alloy 182 in High Temperature Water

Electrochemical Impedance Spectroscopy (EIS) measurements were carried out in high temperature water with Ni-based Alloy-182. The aim was to correlate the EIS results with differences in Stress Corrosion Cracking (SCC) susceptibility that is present around the Ni-NiO transition. There was a clear difference between the EIS results at and away from the Ni-NiO transition. To make a more quantitative correlation a simple equivalent circuit was used to fit the experimental data. A clear correlation between the CPE exponent (n) and the SCC susceptibility could be obtained. Additionally, it was shown that the high frequency arc of the EIS data was related to the diffuse double layer

Insight on the inhibitive property of potassium ion on the stability of shale: a diffuse double-layer thickness (κ−1) perspective

It is believed that potassium ions reduce the hydration energy and swelling of clays and thus promoting stability to shales. This belief was made based on volumetric and linear expansion data obtained from shale and KCl solutions interactions. However, swelling data alone is not adequate to mitigate wellbore instability in shale. Such data must be incorporated with mechanical and physicochemical data for complete and accurate wellbore instability analysis.This paper presents clear experimental evidence showing that concentrated potassium chloride solutions tend to suppress shale swelling as higher concentration of potassium ions collapses the diffuse double layer of clay particles causing shale shrinkage which confirms the notion that the Debye length (κ−1) decreases as the ionic concentration increases.Results show that there exists a KCl concentration threshold above which shale’s compressive strength deteriorates significantly. This concentration threshold was found to hover around 5% by weight. The amount of water and ions uptake into shale was quantified using gravimetric measurements. Significant potassium ions invasion into shale was experimentally measured as KCl solution concentration increased which proved the leaky nature of shale’s membrane. The reduction of shale’s compressive strength seems to be well correlated with the amount of ions uptake into shale. Moreover, data suggests that shale’s compressive strength was not significantly impacted by swelling. It was possible to gravimetrically separate osmotic water from associated water as shale interacted with KCl solutions. Results suggest that osmotic water is responsible for shale swelling since it is unattached to ions which makes it free to move around inside shale. On the other hand, data suggest that associated water does not contribute to shale swelling as it is bound to potassium ions which makes it unfree to move around. It is fair to state, based on our experimental data, that osmotic water is responsible for shale swelling while associated water contributes to shale’s compressive strength alteration.

Macrostructural and Microstructural Properties of Residual Soils as Engineered Landfill Liner Materials

ABSTRACT This study assessed the performance of residual soils with regard to their macrostructural and microstructural properties and compatibility with leachate in pursuit of exploring alternative cost-effective and efficient landfill liner materials. A series of laboratory investigations was conducted on three residual soil samples by using tap water and leachate as permeation fluid to achieve the objectives of the study. The zeta potential measurements revealed that the presence of multivalent cations in the leachate decreased the diffuse double layer (DDL) thickness around the soil particles. The reduced DDL thickness caused a decrease in Atterberg limits of soil-leachate samples and changes in the classification of fine fractions. Additionally, the effects of pore clogging attributed to chemical precipitation and bioclogging were responsible for the reduction in measured hydraulic conductivities of soil-leachate samples. These effects can be clearly observed from the field-emission scanning electron microscopy images of soil-leachate samples with the appearance of less visible voids that led to a more compact and dense structure. The formation of new non-clay minerals and associated changes in the Al and Si ratio as reflected in the x-ray diffraction diffractograms and energy-dispersive x-ray analyses, respectively, were attributed to the effects of chemical precipitation. This study concluded that S1 and S2 residual soil samples are potential landfill liner materials because they possess adequate grading characteristics, adequate unconfined compressive strength, low hydraulic conductivity, and good compatibility with leachate. In contrast, the S3 sample requires further treatment to enhance its properties in order to comply with the requirements of landfill liner materials.

Surrogate Model for Multi-Component Diffusion of Uranium through Opalinus Clay on the Host Rock Scale

Multi-component (MC) diffusion simulations enable a process based and more precise approach to calculate transport and sorption compared to the commonly used single-component (SC) models following Fick’s law. The MC approach takes into account the interaction of chemical species in the porewater with the diffuse double layer (DDL) adhering clay mineral surfaces. We studied the shaly, sandy and carbonate-rich facies of the Opalinus Clay. High clay contents dominate diffusion and sorption of uranium. The MC simulations show shorter diffusion lengths than the SC models due to anion exclusion from the DDL. This hampers diffusion of the predominant species CaUO2(CO3)32−. On the one side, species concentrations and ionic strengths of the porewater and on the other side surface charge of the clay minerals control the composition and behaviour of the DDL. For some instances, it amplifies the diffusion of uranium. We developed a workflow to transfer computationally intensive MC simulations to SC models via calibrated effective diffusion and distribution coefficients. Simulations for one million years depict maximum uranium diffusion lengths between 10 m and 35 m. With respect to the minimum requirement of a thickness of 100 m, the Opalinus Clay seems to be a suitable host rock for nuclear waste repositories.

Effect of ionic concentrations and ph on the Atterberg limit of cohesive soil

The addition of salt to pore water can affect the behaviour of the soil by influencing the electrochemical forces exist between the solid, liquid and dissolved phases. Changes in geotechnical behaviour of fine grained soils under the influence of ionic concentrations and pH depends on the chemistry of the soil constituents and the pore fluid chemistry. The geotechnical modifications of soil behaviour largely depend on the clay particles and the diversities in the nature of the clay types is due to their specific surface and the net electrical charge on them. Generally, clay particles surface are negatively charged while its edges are positively charged. To preserve electrical neutrality the negative charge of the clay particle is balanced by the attraction of cations which are held between the layers, and on the surface of the particles. The charged clay surface together with the counter–ions in the pore water at the diffuse double layer. The present study focuses on the effect of the ionic concentrations of potassium chloride (KCl) and pH on the liquid limit of fine grained soil. Fall cone test was conducted to measure the liquid limit in different concentrations of the pore fluid, with each of the ionic concentrations prepared in four different pH values (3.5, 5.5, 7.5 and 9.5). From the test results, it was observed that the pH values generally has no significant effect on the liquid limit of the samples; while the liquid limit lightly undulated at lower pH values at ionic concentrations of 0.00001 M, 0.0004 M and 0.003 M, the pH values had least influence at higher ionic concentrations (0.1 M and 1.8 M) of KCL. This behaviour is attributed to the buffering effects of the relatively high solute content at 0.1 M and 1.8 M. On the other hand, the liquid limit decreased with increasing ionic concentrations of KCL. Increasing the ionic concentration reduces the thickness of the diffuse double layer thereby depleting the repulsive forces and hence increases the effective stress leading to flocculation of clay particles that gave rise to the reduction in the liquid limit of the clayey sample Keywords: Liquid Limit, potassium chloride, pore fluid, ionic concentrations, pH

Salt diffusion in charged porous media

<p>Some porous media such as clay have charged surfaces. The presence of these charged surfaces results in a complex system where water flow, salt transport, and the electric field are coupled. This system is important in many fields, such as geotechnical engineering, storage of radioactive waste in clay barriers, enhanced oil recovery, and irrigation with marginal water. The charged surfaces alter the transport properties of ions. For example, clay minerals are often negatively charged due to isomorphous substitution. Cations are therefore attracted to the mineral surface, while anions are repelled, creating a diffuse double layer around the clay particle. Cations are therefore transported preferably over anions through such charged pores. To conserve electroneutrality, a streaming potential develops to counteract diffusion by electromigration. This results in smaller effective diffusion coefficients compared to uncharged porous media. We developed a pore-network model to quantify the effect of the double layer processes on the effective diffusion coefficient. Pore-network models are a suitable tool to include the heterogeneity of pore sizes and surface charge densities seen in nature. In pore-network modeling, the geometry of the pore space is simplified, but the network properties are based on realistic statistics such as pore size distribution and connectivity. The larger scale behavior can be identified by averaging over a large number of pores. The results were strongly dependent on the salinity, as this controls the thickness of the double layers. At high salt concentrations, the diffuse double layer is thin and the differences between charged and uncharged porous media are negligible. However, at low salinity, the double layers are thick and the effective diffusion coefficient of salt was reduced by 25% in charged porous media compared to uncharged porous media, due to salt transport being slowed down to conserve electroneutrality. Hence, the presence of charged mineral surfaces can significantly alter transport rates under low salinity conditions.</p>