Occurrence and significance of natural ore-related Ag nanoparticles in groundwater systems

Abstract

Occurrences of Ag nanoparticles (Ag NPs) in the groundwater system have gradually gained extensive attention recently, owing to the wide application and considerable discharge of engineered Ag NPs. However, naturally produced Ag NPs related to metal deposits, which are supposed to have a large source, have largely been ignored. To fill this gap in the research, deep groundwater and nearby well-water samples were collected in several Ag-bearing deposits and subsequently tested using high-resolution transmission electron microscopy (HRTEM). Many approximately spherical shapes of Ag NPs were detected in both types of water media. The characteristics of most Ag NPs in well-water samples were highly consistent with those Ag NPs in deep groundwater samples, both in their morphology features and chemical composition, indicating that those Ag NPs were homologous and originally from the deep concealed Ag-bearing ore bodies. The potential fate of Ag NPs in the groundwater system were addressed, as well, such as their formation in geological processes, separation from the host minerals, migration as a result of water flow and deposition in particular environments. Consequently, Ag NPs in the groundwater systems are supposed to be of great significance in the prospecting for concealed Ag-bearing deposits and the formation of secondary Ag-bearing deposits.