Sander J T Brugman1, Ben L Werkhoven2, Eleanor R Townsend1, Paolo Accordini1, René van Roij2, Elias Vlieg3. 1. Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525AJ Nijmegen, the Netherlands. 2. Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Princetonplein 5, 3584 CC Utrecht, the Netherlands. 3. Radboud University, Institute for Molecules and Materials, Heyendaalseweg 135, 6525AJ Nijmegen, the Netherlands. Electronic address: e.vlieg@science.ru.nl.
Abstract
HYPOTHESIS: Ion adsorption on mineral surfaces depends on several factors, such as the mineral surface structure and the valency, size and hydration of the ion. In order to understand competitive adsorption at mineral surfaces, experimental techniques are required that can probe multiple ionic species at the same time. By comparing adsorption of two different cations, it should be possible to derive the factors governing ion adsorption. Divalent cations are expected to bind stronger to the negatively-charged muscovite surface than monovalent cations. EXPERIMENTS: Here, the competition between the monovalent Cs+ and the divalent Ca2+ cation for adsorption at the muscovite mica basal plane was investigated using surface X-ray diffraction. Using an extended surface complexation model, we simultaneously fit the measured cation coverages and net surface charges reported in literature. FINDINGS: In order to reproduce those complementary data sets, both cation adsorption and anion coadsorption were included in the surface complexation model. Moreover, the intrinsic muscovite surface charge and the maximum of available adsorption sites had to be reduced compared to existing literature values. Competition experiments revealed that the affinity of Cs+ for the muscovite surface is larger than the affinity of Ca2+, showing that hydration forces are more important than electrostatics.
HYPOTHESIS: Ion adsorption on mineral surfaces depends on several factors, such as the mineral surface structure and the valency, size and hydration of the ion. In order to understand competitive adsorption at mineral surfaces, experimental techniques are required that can probe multiple ionic species at the same time. By comparing adsorption of two different cations, it should be possible to derive the factors governing ion adsorption. Divalent cations are expected to bind stronger to the negatively-charged muscovite surface than monovalent cations. EXPERIMENTS: Here, the competition between the monovalent Cs+ and the divalent Ca2+ cation for adsorption at the muscovite mica basal plane was investigated using surface X-ray diffraction. Using an extended surface complexation model, we simultaneously fit the measured cation coverages and net surface charges reported in literature. FINDINGS: In order to reproduce those complementary data sets, both cation adsorption and anion coadsorption were included in the surface complexation model. Moreover, the intrinsic muscovite surface charge and the maximum of available adsorption sites had to be reduced compared to existing literature values. Competition experiments revealed that the affinity of Cs+ for the muscovite surface is larger than the affinity of Ca2+, showing that hydration forces are more important than electrostatics.
Authors: Sander J T Brugman; Paolo Accordini; Frank Megens; Jan-Joris Devogelaer; Elias Vlieg Journal: J Phys Chem C Nanomater Interfaces Date: 2022-05-18 Impact factor: 4.177
Authors: Sander J T Brugman; Anne B Ottenbros; Frank Megens; Willem J P van Enckevort; Elias Vlieg Journal: Cryst Growth Des Date: 2020-05-18 Impact factor: 4.076