Characteristics of congruent dissolution of silicate minerals enhanced by chelating ligand under ambient conditions

Abstract

Abstract Natural and anthropogenic chelating ligands play important roles in promoting mineral dissolution during water-rock interactions. To address the remaining issue of how chelating ligands participate in the dissolution of minerals, this study investigated the dissolution characteristics of seven types of silicate minerals in the presence of a chelating ligand, N,N-bis(carboxymethyl)-L-glutamic acid (GLDA), which is a glutamic acid derivative, through batch dissolution experiments. The results showed that the dissolution of all types of silicate minerals, i.e., olivine (nesosilicate), epidote (sorosilicate), tourmaline (cyclosilicate), enstatite (single-chain inosilicate), hornblende (double-chain inosilicate), biotite (phyllosilicate), and anorthite (tectosilicate), can be enhanced by up to two orders of magnitude at both pH 4 and 8. The chelating ligand particularly facilitated the dissolution of minerals with a higher Al content, such as tourmaline and anorthite. Furthermore, the presence of chelating ligands enhanced the leaching of not only metals but also Si from minerals, resulting in a more congruent characteristic of mineral dissolution. A possible mechanism is that the chelating ligand adsorbs onto the negatively charged the mineral surface, which attracts more H+ and polarizes Si-O and Mg-O bonds, thereby dissolving the minerals at a faster rate. These results have significant implications for understanding the dissolution of minerals in nature and for the application of chelating agents in geological and materials engineering.