de Lary de Latour, L, Guérin, V, Gatellier, C & Piat, C 2022, 'Implementing phytostabilisation for tailings deposits remediation: project design and feedback from case studies in France', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: 15th International Conference on Mine Closure
, Australian Centre for Geomechanics, Perth, pp. 1219-1230, https://doi.org/10.36487/ACG_repo/2215_90
Due to economic and environmental reasons, French mines closed down in the 19th and 20th centuries. In 2012, a legacy of more than 2000 metallic mine waste deposits was identified in the framework of an inventory resulting from the European Directive on the management of wastes from extractive industries. The dispersion of solid particles, especially tailings due to their fine grain size, can contribute risks to the environment and specifically to surface water through transport and leaching. Waste deposits with bare surfaces can result in significant transfers of sediments through hydraulic erosion. In this context, phytostabilisation strategies are valuable remediation options to mitigate the risk of transfer. However, only a few full-scale phytostabilisation implementations have yet been completed in France.
This paper deals with the deployment of phytostabilisation to remediate legacy tailings deposits in the French context, focusing on operational aspects and feedback from several case studies (former Ag-Pb mines from Massif Central and Sn and Au mines from the Pays-de-la-Loire region). Phytostabilisation relies on the use of plants and amendments to reduce mobility of pollutants in soil and transfers trough environment. In the French context, the aim is to reduce, to an acceptable level, transfers from waste deposits to the surrounding environment, particularly due to surface erosion and, to a lesser extent, leaching.
Conventional approaches to confining mining waste are mainly based on water management, landform design and covering the soil with subsequent revegetation. With this approach, plants are used to stabilise the soil layer that has been deposited above the tailings. Thus, plants do not directly stabilise mine tailings, as is the case with phytostabilisation strategies. From case studies, we show that evaluating the benefits of phytostabilisation requires using appropriate new criteria for the cost-benefits analysis in order to capture the ecosystem services that control the stabilisation process (ecosystem services such as soil creation, water regulation, erosion reduction). Costs are expected to be lower because it tends to minimise intervention. Furthermore, long-term perspectives, technology readiness, constraints due to access and site immobilisation, costs of remediation and maintenance and social perception are key criteria that also require appropriate evaluation.
As biological organisms, plants have inherently variable responses that must be considered in project management. Thus, based on case studies, strategies have been developed to tackle uncertainties by implementing laboratory and pilot tests. A phytostabilisation project needs a sound understanding of site functionality that can be synthetised on a conceptual site model. Based on a case study, we show that design at a detailed scale can optimise phytostabilisation solutions. Evaluation of pollutant fluxes enables prioritisation of actions on zones with critical transfers. Identification of stable (no transfers) zones due to spontaneous vegetation minimises intervention, costs and ecological impact. To complement phytostabilisation, other solutions are necessary to reduce erosion on critical zones or adapt the technology to site constraints (e.g. soil cover, fascines, areas for rainwater infiltration).
Perspectives for long-term site evolution are then discussed in terms of the solutions implemented (conventional or phytostabilisation). Return of experience still needs to be gathered in the years to come in order to improve management by phytostabilisation.
Keywords: phytostabilisation, tailings, mine waste, erosion, ecosystem services.
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