Computational insights into the Adsorption Mechanism of Gallic acid/ Pyrogallic acid/Tannic acid on Calcium-bearing Mineral Surfaces

摘要

From a novel spatial geometry aspect, the adsorption mechanism of gallic acid (GA), pyrogallic acid (pyGA) and tannic acid (TA) were investigated via using the quantum mechanics (QM) calculations and the forcefield based molecular mechanic (MM) approaches. The obtained geometry, ionization energies of proton and molecular orbitals of GA showed that the deprotonation of GA would preferentially occur at the 1-COOH and 4-OH sites. This could be the potential site for chelation of metal ions. The further first principles calculations results in both geometry and thermodynamics indicated that the dissociated GA/pyGA could bind with the fluorite surface more strongly than bind the calcite surface. However, MM results showed an opposite conclusion that TA preferred to adsorb onto the calcite surface rather than the fluorite surface. Further analysis results of the geometry of TA@surface presented the stronger adsorption of TA@calcite surface was the result of more surface Ca-0 bonds indicating that the calcite surface exposed calcium atoms was well-matched with the TA active sites, while the fluorite was not. This work from a molecular level reveals the adsorption mechanism of GA bearing reagents, pyGA and TA on fluorite and calcite, respectively. These findings put emphasis on the spatial geometry influence of a large molecule, and sheds new light to the developing of new flotation reagents via considering the influence of the spatial structure of a molecule.