Probing the Role of Water Chemistry on the Behavior of Clays in Process and Natural Environments Using Solution Calorimetry

Clays, due to their specific surface area and electrical charge density, are among the most active minerals in aquifers, oil and gas reservoirs, and tailings ponds. Important problems, such as limited yield of oil recovery during petroleum exploration, involve the interaction of process fluids with minerals which constitute reservoir pore walls. During mine tailings treatment and management, water chemistry impacts the aggregation and settling of clays. Solution calorimetry is a sensitive probe for species transfer to and from clay surfaces, and for the measurement of the effects of water chemistry (temperature, pH, salinity) on clay particle surfaces, in this case, kaolinite, illite, and montmorillonite. In this work, we show that interactions between clays and surrounding water are temperature-independent for all three clay types and that water chemistry has no measurable effect on the surface properties of illite. For kaolinite, water pH does impact surface properties and has a synergistic impact with salinity at high pH. The surface properties of montmorillonite are sensitive to water pH and salinity. These data and observations extend a solution enthalpy modeling framework for clays and contaminated clays in water and liquid hydrocarbons. In the next phases of this work, entropic effects will be addressed so that a quantitative Gibbs free energy modeling framework for the enthalpy of solution of clays can be constructed and linked to clay settlement kinetics

Probing the Impact of Asphaltene Contamination on Kaolinite and Illite Clay Behaviors in Water and Organic Solvents: A Calorimetric Study

A detailed understanding of the impacts of trace compounds and asphaltene adsorption on the behavior of clays contributes to the development of production processes for heavy oils and bitumen with lower environmental impacts, to the treatment of tailings from mined bitumen, and to the mitigation of impacts from oil spills in natural environments. Probes, such as solution calorimetry, are sensitive to species transfer to and from clay surfaces and outcomes can be interpreted unambiguously when supplemented with thermogravimetric analysis and scanning electron microscopy measurements. In this study, the effects of asphaltene coating on the enthalpy of solution of kaolinite and illite clays in toluene, <i>n</i>-heptane, and deionized water were investigated at 60 °C and atmospheric pressure. Asphaltene coating increases organic compound sorption but does not impact water sorption vis-à-vis uncoated clay particles or water displacement from clay particles by organic liquids as solvents or as trace contaminants in water. Experimental outcomes are interpreted using a quantitative mass and energy balance model framework that isolates terms for solvent and trace contaminant sorption/desorption and surface energy effects. Mechanistic and quantitative insights underlying the stability of asphaltene-coated clay dispersions in tailings ponds and the behaviors of these clays in diverse industrial and natural environments are discussed

Probing Contaminant Transport to and from Clay Surfaces in Organic Solvents and Water Using Solution Calorimetry

Clays, in tailings, are a significant ongoing environmental concern in the mining and oilsands production industries, and clay rehabilitation following contamination poses challenges episodically. Understanding the fundamentals of clay behavior can lead to better environmental impact mitigation strategies. Systematic calorimetric measurements are shown to provide a framework for parsing the synergistic and antagonistic impacts of trace (i.e., parts per million level) components on the surface compositions of clays. The enthalpy of solution of as-received and “contaminated” clays, in as-received and “contaminated” organic solvents and water, at 60 °C and atmospheric pressure, provides important illustrative examples. Clay contamination included pre-saturation of clays with water and organic liquids. Solvent contamination included the addition of trace water to organic solvents and trace organic liquids to water. Enthalpy of solution outcomes are interpreted using a quantitative mass and energy balance modeling framework that isolates terms for solvent and trace contaminant sorption/desorption and surface energy effects. Underlying surface energies are shown to dominate the energetics of the solvent–clay interaction, and organic liquids as solvents or as trace contaminants are shown to displace water from as-received clay surfaces. This approach can be readily extended to include pH, salts, or other effects and is expected to provide mechanistic and quantitative insights underlying the stability of clays in tailings ponds and the behaviors of clays in diverse industrial and natural environments

Gold Core Nanoparticle Mimics for Asphaltene Behaviors in Solution and at Interfaces

Asphaltenes are a poorly defined class of self-assembling and surface active molecules present in crude oils. The nature and structure of the nanoaggregates they form remain subjects of debate and speculation. In this exploratory work, the surface properties of asphaltene nanoaggregates are probed using electrically neutral 5 nm diameter gold-core nanoparticles with alkyl, aromatic, and alkanol functionalities on their surfaces. These custom synthesized nanoparticles are characterized, and their enthalpies of solution at near infinite dilution and the interfacial tensions of solutions containing these nanoparticles are compared with the corresponding values for Athabasca pentane asphaltenes. The enthalpies of solution of these asphaltenes in toluene, heptane, pyridine, ethanol, and water are consistent with the behavior of gold-alkyl nanoparticles. The interfacial tension values of these asphaltenes at toluene–water and (toluene + heptane)–water interfaces are consistent with the behavior of gold-biphenyl nanoparticles as are the tendencies for these asphaltenes and gold-biphenyl nanoparticles to “precipitate” in toluene + heptane mixtures. Gold-alkyl nanoparticles are minimally surface active at toluene–water and (toluene + heptane)–water interfaces and remain dispersed in all toluene + heptane mixtures. The behavior of these asphaltenes in solution and at interfaces is inconsistent with the behavior of gold-<i>n</i>-alkanol nanoparticles. The outcomes of this formative work indicate potential roles for aromatic submolecular motifs on aggregate surfaces as a basis for interpreting asphaltene nanoparticle flocculation and interfacial properties, while alkyl submolecular motifs on aggregate surfaces appear to provide a basis for interpreting other aspects of asphaltene solution behavior. A number of lines of inquiry for future work are suggested