Taking into account final mining wastes in LCA: How to quantify the impacts of tailings?

International audienceIn 2014, the European Union generated more than 700 million tons of waste in the mining and quarrying sector. Tailings are one typology of mining wastes and are generated during the mineral processing steps of metal production. If technology feasible and economically viable, these wastes can be reprocessed to extract still remaining valuable resources. If not, these wastes are stocked is so called "tailings ponds" or "tailings dams" for a very long period that can extend beyond the mine closure. As tailings are resulting by-products of metallurgical processes, they often contain potentially hazardous elements that can have negative impacts on nearby waters and soils. So far, only few life cycle assessment (LCA) studies consider the environmental impacts of tailings storage and management on metal production. The Ecoinvent database proposes two generic datasets concerning sulfidic and non-sulfidic tailings disposals. Nevertheless, tailings composition is linked to the type of ore treated, to the type of processing technologies used and to the geological and climatic conditions of the tailing storage. Thus, environmental impacts of tailings storage are site-specific in addition of being time-dependent. In fact, emissions can occur in a short (yearly) or a long time frame. Assessing the timely dependent behavior of tailings and in particular the interactions between the tailings pond and the surrounding groundwater and underground can be done using reactive transport modeling. The aim of this presentation is to show how the results of geochemical modelling can be used in LCA to take into account the emissions induced by tailings in metal production. This work will be illustrated with a mining plant producing copper, other metallic by-products and their associated sulfidic tailings. In a first place, the tailings pond and its associated characteristics (hydrodynamic properties, chemical composition of the pore water and mineralogical composition) are modeled alongside with the chemical composition of the tailings and its boundaries, initial and climatic conditions. Reactive transport of the chemical compounds of the tailings between the pond and the environment is simulated in order to quantify the specific emissions from the tailings in a time dependent scale. These quantifications are direct inputs for the life cycle inventory of the tailings management. Coupling geochemical modelling with LCA allows taking into consideration, for a given mine site, the impacts of tailings management in the LCA of metal production. This allows assessing the contribution of tailings against the other life cycle stages of metal production. Considering the resulting impacts of mining wastes also allows to better take into account the environmental benefits of mining waste retreatment