Mobility of Strategic Elements in Chilean Tailings in the Context of Secondary Mining Processes

摘要

After a long time of dumping, tailings are characterized by hydrogeochemical reorganization processes that are reflected in weathering zones (mobilization) and accumulation zones (immobilization). These processes are connected to substantial secondary mineral formation. Accumulation zones are thereby often connected to iron phases and also have an increased content of trace elements. This knowledge is relevant for Chilean mining dumps because some of them are already affected by these long time processes.Chilean mining companies are interested in information on the occurrence and extractability of secondary minerals and strategic elements (minor and trace elements of economic interest) from tailings. The German-Chilean project SecMinStratEl (Secondary Mining of Strategic Elements) aims to provide an understanding of the accumulation processes and will also evaluate opportunities for selective extraction. The project is actively supported by significant Chilean mining companies and universities.Tailings considered in the study consist of granular material, which was ground during primary mining. Due to its potential content of elements of economic importance, the material is nowadays becoming an interesting resource for secondary mining. Exposed tailings suffer from weathering processes; mine waters, especially dump leachates, are enriched in some metals and trace elements which may also constitute a potential environmental hazard.By means of specific characterization of accumulation horizons in dumps, a description of metal contents and their mobilization behavior is possible. Differentiation between the elemental contents of different layers is achieved with XRF analyses. Furthermore, a sequential extraction is performed in order to describe the partitioning of elements in mineral phases. Thus, the extractability of major, minor and trace elements can be estimated. With these findings, conclusions about extraction technologies for these elements and the environmental risk potential can be made.