Composition in the Interface between Clay Mineral Surfaces and Divalent Cation Electrolytes

Abstract

The interfacial free energy of a solid, which determines its adsorption properties, depends on interactions between the surface and the fluid. A change in surface composition can completely change the behavior of the solid. Decades of work have explored adsorption and its effects at solid-fluid interfaces from the macroscopic perspective and using molecular modeling, so the concept of the electric double layer (EDL) is well established in the community. However, direct, molecular level, experimental observations of the composition within the interface region, and its change with time and conditions, are not abundant. We used cryogenic X-ray photoelectron spectroscopy (cryoXPS) to observe the composition in the clay mineral-solution interface region as a function of bulk solution composition, on illite and chlorite in MgCl and CaCl electrolytes, over a range of concentrations (1-125 mM), in situ, on vitrified samples. These samples were prepared from very thin smears of centrifuged wet paste that were instantaneously chilled to liquid N temperature. They preserved the adsorbed solution in its amorphous state, maintaining the location of the ions and water with respect to the solid, without the disruption that occurs during drying or the rearrangement that results as water crystallizes during freezing. With decreasing ionic strength, we could directly monitor the loss of negative charge in the interface region, producing an anion deficiency, as predicted by theory. The Cl/Me ratio dropped below 1 for chlorite at 12-25 mM MeCl and for illite at 75-100 mM. In addition to better understanding of clay mineral behavior in solution, this work demonstrates that only those clay minerals where surface charge density is the same or lower than that for chlorite contribute to a low salinity enhanced oil recovery response (LS EOR). This explains many of the contradictory results from studies about the role of clay minerals in LS EOR.

Geochemical Modeling and Microfluidic Experiments To Analyze Impact of Clay Type and Cations on Low-Salinity Water Flooding

“…Clay swelling was not observed as well. There are two mechanisms behind clay swelling: crystalline swelling and osmotic swelling. ,− Crystalline swelling happens in all types of clay minerals, especially in the smectite group (montmorillonite). Montmorillonite, which has a large basal exchange capacity (90–150 meq/100 g), will readily adsorb Na + and other hydrating cations.…”

“…However, in the context of low-salinity effect (LSE), an explanation has been rarely suggested so far, which clarifies why different clay minerals have different sensitivities to the change of salinity and ionic composition of brines, which in turn leads to different extents of wettability alteration. Only very recently, Jelavićet al 15 used cryogenic X-ray photoelectron spectroscopy to observe the composition in the clay mineral−brine interface region on illite and chlorite in MgCl 2 and CaCl 2 electrolytes over a range of concentrations. They concluded that since during LSW injection the concentration of (Ca 2+ + Mg 2+ ) dropped from 69 to 4 mM, a mineral with a threshold concentration of (Ca 2+ + Mg 2+ ) that lies between 4 and 69 mM would then respond to lowering of the ionic strength.…”

Survival of environmental DNA in sediments: Mineralogic control on DNA taphonomy

“…Surface charge density plays an important role in the behaviour of electrolytes and polymers near surfaces (Israelachvili 2015;Jelavić et al 2018). We fixed a positively, densely charged polymer on a flat mica substrate and tested if the adsorbed DNA would depend on the ionic potential of the background ion where Na+ represented a cation with low ionic potential and Ni2+ a cation with high ionic potential.…”

Mechanistic Insight into Biopolymer Induced Iron Oxide Mineralization Through Quantification of Molecular Bonding

“…The suspensions were left to equilibrate for 18 hours in 15 ml PET tubes. The data acquisition protocol was previously described by Jelavić et al 70 In short, the suspensions were ultracentrifuged for 10 min and the supernatant was decanted, a small amount of the wet sediment was transferred directly to the XPS antechamber precooled with liquid nitrogen to ~170 ⁰C where the wet paste immediately vitrified. The sample was then transferred to the analysis chamber also cooled at ~170 ⁰C with liquid nitrogen and analysed, under ultrahigh vacuum conditions, ~10 -9 Torr (V-vitrified sample).…”