Gibbsite (100) and Kaolinite (100) Sorption of Cadmium(II): A Density Functional Theory and XANES Study of Structures and Energies

Abstract

Due to the potential toxicity of cadmium (Cd 2+ ) and its presence in various waste products found in the environment, it is necessary to develop methods to attenuate and remediate Cd 2+ waste. Sorption of Cd 2+ to mineral surfaces is a potential route to accomplish this goal. This work focused on improving our molecular-scale understanding of the chemistry of Cd 2+ interactions with gibbsite and kaolinite mineral surfaces. Plane-wave density functional theory (DFT) energy minimization calculations and molecular dynamics simulations were used to study the adsorption energies and the nature of the bonds between Cd 2+ and the mineral surfaces for possible inner-and outer-sphere surface complexes. Models resulting from the DFT calculations were used to calculate theoretical XANES spectra that were compared with experimental Cd L III XANES of aqueous Cd 2+ as a proxy for outer-sphere Cd 2+ hydrated complexes associated with the mineral surfaces. These studies suggest that Cd 2+ would favorably bond to the (100) surfaces of both kaolinite and gibbsite through a bidentate mononuclear interaction. However, the results indicate that mixtures of surface complexes on these minerals are likely.

Connecting Thermodynamics of Alkali Ion Exchange on the Quartz (101) Surface with Density Functional Theory Calculations

“…Model electronic energies were calculated using geometry optimizations by DFT. , Calculations were performed using the Vienna Ab initio Simulation Package (VASP) software. − The method used in VASP for the geometry optimizations was the density functional PBE0, , coupled with the Si, O, H, Li_sv, Na_sv, K_sv, and Rb_sv pseudopotentials . The initial models were geometry-optimized with VASP using accurate precision (PREC), a cutoff energy of 48,000 kJ·mol –1 (ENCUT), and an EDIFF value of 9.6 × 10 –4 kJ·mol –1 .…”

“…27−29 The method used in VASP for the geometry optimizations was the density functional PBE0, 30,31 coupled with the Si, O, H, Li_sv, Na_sv, K_sv, and Rb_sv pseudopotentials. 32 The initial models were geometryoptimized with VASP using accurate precision (PREC), a cutoff energy of 48,000 kJ•mol −1 (ENCUT), and an EDIFF value of 9.6 × 10 −4 kJ•mol −1 .…”

“…The calculated E results reflect all of the structural changes that occurred during the unconstrained geometry optimization calculations, not just the group I cation-exchange portion of the energy. However, the calculated ΔE ex results are considered equivalent to the energy of the group I cationexchange energy 32 because these types of water restructuring changes are presumed to occur in the real systems as well. Hence, ΔE ex results can be compared with experimental group I cation-exchange enthalpies from Allen et al 20 In addition to discussing the ΔE ex results and how they compare with experimental data, we will compare the coordination chemistry of the group I cation model results with available data from the literature.…”

Applying Red Mud in Cadmium Contamination Remediation: A Scoping Review

“…Metal oxides represent a substantial proportion of the red mud sorption potential. Gibbsite, the predominant Al oxide found in red mud, can bind Cd 2+ through a bidentate mononuclear bond [58]. The Fe oxides hematite and goethite can electrostatically adsorb Cd and bind Cd through ternary complexes with anions such as phosphorus [59].…”