Testing the hypothesis that solvent exchange limits the rates of calcite growth and dissolution

N Rampal and HW Wang and AB Brady and JM Borreguero and D Biriukov and E Mamontov and AG Stack, RSC ADVANCES, 14, 15743-15754 (2024).

DOI: 10.1039/d4ra00565a

It is established that the rates of solvent exchange at interfaces correlate with the rates of a number of mineral reactions, including growth, dissolution and ion sorption. To test if solvent exchange is limiting these rates, quasi-elastic neutron scattering (QENS) is used here to benchmark classical molecular dynamics (CMD) simulations of water bound to nanoparticulate calcite. Four distributions of solvent exchanges are found with residence times of 8.9 ps for water bound to calcium sites, 14 ps for that bound to carbonate sites and 16.7 and 85.1 ps for two bound waters in a shared calcium-carbonate conformation. By comparing rates and activation energies, it is found that solvent exchange limits reaction rates neither for growth nor dissolution, likely due to the necessity to form intermediate states during ion sorption. However, solvent exchange forms the ceiling for reaction rates and yields insight into more complex reaction pathways. Using neutron scattering dynamics measurements to validate molecular dynamic simulations, it is found that the rates of solvent exchange are not likely to limit the rates of calcite crystal growth and dissolution.

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