Adsorption behavior of oxalic acid at water-feldspar interface: experiments and molecular simulation

Feldspar belongs to aluminosilicate minerals with a huge reserve, accounting for at least 98% in soil minerals. Oxalic acid is the common organic matter in the natural world, having three configurations (H2C2O4, HC2O4- and C2O42-) dependent on pH value in water solution. In this work, the adsorption behavior of oxalic acid at water-feldspar interface were investigated at the molecular level through molecular dynamic simulation and advanced characterization technologies in order to provide the useful information for bioleaching and flotation industry. Classical molecular dynamic (MD) simulation, density functional theory (DFT) calculation and frequency calculation were performed to analyze adsorption behavior of oxalic acid at water-feldspar interface. Adsorption of H2C2O4 on feldspar surface belonged to physical outer-sphere adsorption with hydrogen bond while adsorption of HC2O4- and C2O42- belonged to inner-sphere adsorption with Al-O bond based on the molecular dynamic simulation results. Frequency calculation demonstrated both HC2O4- and C2O42- complexed with Al active site rather than Si site on feldspar surface, and the detected ATR-FTIR spectra were also in agreement with the simulated results. Dissolution experiments of feldspar with oxalic acid and TGA-DSC analysis of feldspar after oxalic acid adsorption were carried out to evaluate the adsorption behavior. Adsorption mechanism of oxalic acid on feldspar surface was proposed.