Changes of structure and micromorphology of muscovite in the process of its interfacial reaction with acidic solutions

The dissolution of silicate minerals is of great importance to many geochemical processes. In order to better comprehend the dissolution properties of muscovite, the dissolution process of cations, and the changes of structure and microstructure of muscovite in aqueous interfacial reaction with oxalic acid and sulfuric acid solutions have been studied in this paper. The changes of composition, structure and morphology of muscovite in the process of its interfacial reaction with acidic solutions have been characterized by using ICP-OES, XRD, SEM and AFM methods. The results show that the dissolution rates of cations from muscovite in sulfuric acid solution are relatively high, due to the relatively large concentration of H+ in sulfuric acid solution at the initial stage of the reaction. With the progress of the reaction, oxalic acid solution resulted in a rapid dissolution of Si4+, Al3+ and K+ from moscovite. This can be attributed to the weakening of bond energy of moscovite and reduction of the H+ repulsion on the surface of muscovite caused by the adsorption of oxalate anionic ligands on the surface of muscovite. In the reaction process of muscovite with oxalic acid and sulfuric acid solutions, the dissolution rate of K+ is higher than those of Al3+ and Si4+, which is related to the binding force between ions. After the reaction of muscovite with oxalic acid solution, the concentration ratio of dissolved Al3+ and Si4+ (Al/Si value) is increased gradually with the extension of reaction time. However, after the reaction of muscovite with sulfuric acid solution, the Al/Si value is changed in an opposite trend. This difference is due to the fact that the complexation of Al3+ by oxalate anion ligands resulted in the accelerated dissolution of Al3+ in structure of muscovite, while the complexation of Si4+ by oxalate anion ligands resulted in weak influence on the dissolution of Si4+ in structure of muscovite. After the reactions of muscovite with oxalic acid and sulfuric acid solutions, banded corrosion pits appeared on the surface of muscovite, which was related to the preferential dissolution of the defect site of muscovite. The formation of the corrosion pits resulted in the attack of proton and ligand on the exposed new edge surface (hk0), then caused the increase of size of corrosion pit more than the increase of depth.