Morphological features of quartz dissolved in Humic acid

Abstract

Quartz dissolution plays a significant role in controlling the concentration of silica in hydrothermal systems, thus providing controls on natural waters and artificial systems. However, the kinetics of quartz dissolution, particularly in humic acid, is yet to be clearly elucidated, because of the varying explanations proffered in different studies. Therefore, this study reviews the empirical quartz dissolution models to present a unified approach. In addition, quartz grains were dissolved in humic acid and then characterized using scanning electron microscopy and Fourier Transform Infrared (FTIR). The review postulates that dissolution mechanism of the quartz in acidic solutions involves the reaction of the metal atoms with water to form solvated cations, and subsequent reaction of the silicate groups with H+ to form hydrated anions. Thus, quartz surface is intensely etched after dissolution to form varying degrees of deep etch pits and flat overlapping crystal faces. Concomitant with the quartz dissolution is the adsorption of humic acid onto the quartz surface via hydrogen-bond interaction. Fibrous and wiry structures as well as platelets of the humic acid molecules accumulating in the etch and dissolution pits and plaster the quartz surface. Therefore, in addition to mineral dissolution, humic acid serves as organic binders in siliciclastics. This study posits the dissolution of quartz in humic acid creates surface defects such as etch pits and leads to associated adsorption of humic acid molecules on the quartz surface via hydrogen-bond interaction.