Understanding the exchange properties of Group I cations on mineral surfaces is necessary to address the challenge of remediating Li+ contamination from batteries and radioactive Rb+ contaminants from nuclear waste and nuclear power plant disasters. Gaining insight into the molecular-level chemistry of Group I cation interactions with mineral surfaces will allow improved prediction of their behavior in the environment. This work used periodic density functional theory (DFT) coupled with pseudopotentials in the Vienna Ab-initio Simulation Package (VASP) to model the exchange of Li+ with Na+, K+, or Rb+ at the quartz (101)-water interface. The purpose of these calculations was to determine the thermodynamics of ion exchange, the coordination numbers of the Group I cations, and their H-bonding environments, all of which were compared with experimental thermodynamic data from our group or with bonding environment data from the literature. The effect of SiO- vs. SiOH quartz (101) surface moieties on thermodynamics was also explored. This work used neutral periodic models of quartz (101) with stoichiometries of Li(ads)A(aq)Si72O221H154Cl2 and A(ads)Li(aq)Si72O221H154Cl2, where A is Na+, K+, or Rb+. The adsorbed (ads) Group I cation was initially bonded to the quartz (101) surface through either a SiO- or SiOH moiety. In all cases, ΔE of cation exchange are the most exothermic when Li+ desorbs and goes into aqueous solution, the other Group I ion of interest moves from aqueous solution to the surface as an outer-sphere cation, and a proton transfers from the aqueous solution to the SiO- moiety on the surface. The coordination numbers, Group I+-OSi bond distances, and Group I+-OH2 distances agreed with the literature data within the errors of the results and data.

Exchange of Na+, K+, or Rb+ with Li+ on the quartz (101) surface: Comparison of periodic DFT results with experiment

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.