Experimental and Modeling Investigation of Factors Affecting Crud Deposition in PWRs: Role of Zn, Ni, and Redox Potential

Corrosion products such as nickel-iron spinel oxides (known as CRUD) in the coolant circuits of pressurized water (PWR) reactors may lead to particulate fouling, negatively impacting power distribution and changing local chemistry. The transport and deposition of particles depend in part on the surface charge of the particles and the nearby surfaces. Tuning coolant chemistry and the composition of the primary circuit materials has been used as an empirical lever for CRUD mitigation, but experimentation is limited by a variety of other constraints in a working reactor. To simulate the transport and deposition process of CRUD particles, a multiscale multi-physics model was designed for a simple geometry representing hot/cold leg piping with fluid properties reflecting a PWR environment. A macro-scale model solves for the fluid flow and particle trajectories and is later coupled with a fine-scale particle adhesion model. To ensure the relevance of the fine-scale model, surface properties of synthetic CRUD particles covering a range of compositions and water chemistry (Zn addition and reducing environment) were measured and incorporated into the simulations. Preliminary results of the fine-scale simulations examining the effect of the surface potential of the CRUD particles and the pipe surface are consistent with expectations from DLVO (Derjaguin, Landau, Verwey and Overbeek) theory and support observations from test loop experiments.

DLVO theory applied to TiO 2 pigments and other materials in latex paints

Chapter Three - The Extended DLVO Theory

Aggregation and charging of natural allophane particles in the presence of oxyanions

Colloidal stability and charging behavior of amidine latex particles in the presence of multivalent oligomers of acrylic acid was investigated by electrophoresis and light scattering. The data were interpreted quantitatively with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO) whereby the surface potentials were estimated from electrophoresis. Monomer leads to slow aggregation at low concentrations and to rapid aggregation at high concentrations, as characteristic for simple salts. The oligomers induce a charge reversal of the particles. Close to the isoelectric point (IEP) aggregation is rapid while the suspension becomes stable away from this point. At high oligomer concentrations, the aggregation becomes rapid again. The agreement between DLVO theory and experiment is good close to the IEP. At higher oligomer concentrations, the theory predicts larger stabilities than observed experimentally. While inter-particle forces seem to be well described by DLVO theory near the IEP, additional attractive non-DLVO forces are becoming relevant at higher concentrations.

Understanding the role of brine ionic composition on oil recovery by assessment of wettability from colloidal forces

Demand for titanium dioxide pigments improves in second quarter

Revisiting DLVO theory to inform particle-scale modelling of clays

The role of microbial surface properties and extracellular polymer in Lactococcus Lactis aggregation

Chapter Eight - Stability Versus Flocculation of Aqueous Particle Suspensions

DLVO Theory and Clay Aggregate Architectures Formed with AlCl 3

Five parameters, including specific surface area, surface potential, charge density, electrostatic field strength and charge number on the solid-liquid interface, are important surface properties of charged nano-colloidal particles. Currently, although the specific surface area (outer surface area) can be instrumentally determined through inert gas adsorption, there is no instrument that can determine the other four surface properties, let alone give a combined measurement. A new method for the combined measurement of five surface properties by Na(+)- and Ca(2+)-selective electrodes with a potentiometer was developed, which can give precise results with good repeatability from the measurements. Besides, this new method bears three other significant advantages: (1) for the first time, the surface potential and total surface area (both inner and outer surface areas) of particles can be easily determined with a potentiometer, (2) the enhanced dispersion forces of counterions in the surface electrostatic field from charged particles were considered and (3) a combined measurement of the five surface properties can be done with a potentiometer. The combined measurement means that the five surface properties of particles can be determined under identical conditions, which is very important for the study of interface reactions in aqueous solutions. Based on the method, a new apparatus for the combined measurement of the five surface properties of nano-colloidal particles can be developed.

Particle transport within the Berea, Noxie and Cleveland sandstones having mean pore sizes of 10, 15 and 30 microns, respectively, was studied by injection of aqueous suspensions of sand particles having mean particle sizes of 4, 6 and 7 microns. A constant flow rate was used, and the pressure drop across the core was continuously monitored. The pressure drop across the core was continuously monitored. The effluents were collected in a fraction collector, and the number of particles per milliliter and distribution of sizes of the particles were determined using a particle counter interfaced particles were determined using a particle counter interfaced with a computer. These data were used to postulate a theory of discrete particle transport within porous media from a statistical point of view. A statistical random walk model was developed using Poiseuille's capillary flow equation and the actual pore size distribution of the core to calculate the pressure drop across the core. Particles are selected using a pressure drop across the core. Particles are selected using a random number generator and the actual particle size distribution, and are tested for passage through the most probable capillary with a pressure threshold function. If the particle posses, another particle is generated; however, if the particle posses, another particle is generated; however, if the particle lodges, a new pressure is calculated, and each capillary is tested for particle breakout with the new pressure. This process is continued until a plugging pressure is attained or a process is continued until a plugging pressure is attained or a maximum number of particles pass through the core. The calculated pressures and distributions of effluent particles closely approximate the experimentally observed data. The process of particle transport, where colloidal forces are process of particle transport, where colloidal forces are negligible, is a random statistical process which can be represented by a statistical mathematical model. Introduction This work was initiated to develop a practical mathematical approach to particle transport within porous systems and the formation of a filter-cake at the face of the porous medium. This subject has previously been treated as a mass balance problem leading to experimental determination of numerous time dependent coefficients for the filtration process. Under these circumstances, each change of suspension process. Under these circumstances, each change of suspension or filter must be tested experimentally before mathematical analysis con be applied. However, the process of filtration is a natural statistical phenomenon since it results from the behavior of a porous medium having a distribution of pore sizes being contacted by a suspension containing a distribution of particles of various shapes and sizes. Hence, a statistical random walk mathematical model was developed using Poiseuille's capillary flow equation, the pore size distribution of the core, and the particle size distribution of the suspension. The model approximates the pressure fluctuations of the system, the cake build-up, and the transport of fine particles through the rock. At this stage of development, the model may be used for analysis of various processes involving the transfer of discrete particles in porous media in the absence of colloidal attractive forces. Three applications that are of immediate interest are:filtration of fluids prior to injection,selective plugging of high permeability prior to injection,selective plugging of high permeability zones anddrilling mud penetration. This work will be continued with specific application to well logging problems since the accurate measurement of oil saturation is a critical aspect of enhanced oil recovery. LITERATURE REVIEW The principal mechanisms that cause deposition during transport of particles within a porous medium are sedimentation, direct interception and surface attractive properties of the particles and medium. The path of fluid flow within a geologic porous system is a tortuous one which is subject to frequent sudden changes in direction and velocity. Suspended particles with densities greater than the density of the carrier fluid will not follow the stream lines as the fluid suddenly changes direction of flow and will impinge on the walls of the pores due to forces inherent in gravity and inertia. Particles thus deposited will tend to form domes as observed experimentally (1,2,3).

Purification of graphite from spent carbon cathodes through the reduction of the mechanical entrainment of cryolite using polyaluminium chloride as a flocculant

Nano-sized iron colloids are formed as acid mine drainage is exposed to surface environments and is introduced into surrounding water bodies. These iron nanomaterials invoke aesthetic contamination as well as adverse effects on aqueous ecosystems. In order to control them, the characteristics of their behaviour should be understood first, but the cumulative research outputs up to now are much less than the expected. Using zero-valent iron (ZVI) and magnetite, this study aims to investigate the behaviour of iron nanomaterials according to the change in the composition and pH of background electrolyte and the concentration of natural organic matter (NOM). The size and surface zeta potential of iron nanomaterials were measured using dynamic light scattering. Characteristic behaviour, such as aggregation and dispersion was compared each other based on the DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory. Whereas iron nanomaterials showed a strong tendency of aggregation at the pH near point of zero charge (PZC) due to electrostatic attraction between particles, their dispersions became dominant at the pH which was higher or lower than PZC. In addition, the behaviour of iron nanomaterials was likely to be more significantly influenced by cations than anions in the electrolyte solutions. Particularly, it was observed that divalent cation influenced more effectively than monovalent cation in electrostatic attraction and repulsion between particles. It was also confirmed that the NOM enhanced the dispersion nanomaterials with increasing the negative charge of nanomaterials by coating on their surface. Under identical conditions, ZVI aggregated more easily than magnetite, and which would be attributed to the lower stability and larger reactivity of ZVI.