Passive treatment of acid mine drainage with active geocomposites

Authors: Martins, G; Niewerth, S; Cheah, C Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2215_20

Cite As:
Martins, G, Niewerth, S & Cheah, C 2022, 'Passive treatment of acid mine drainage with active geocomposites', in AB Fourie, M Tibbett & G Boggs (eds), Mine Closure 2022: Proceedings of the 15th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 321-328, https://doi.org/10.36487/ACG_repo/2215_20



Abstract:
Mining of finite resources inevitably leaves open pits and shafts after the mines are closed. Ideally, natural rehabilitation takes place, and the surrounding environment is re-established. However, the environment and the surface water still need to be protected. Rainfall corrodes rock and leaches metals and metalloids, such as aluminium, copper, iron, or nickel, into surface water. Interacting with high acidity, these substances pose an environmental risk to plants and animals. Vertical flow ponds or channels are a passive approach to mine water remediation. Surface drainage water is diverted to these retention ponds. In ‘conventional’ vertical flow ponds, metal-contaminated water percolates through a thick layer of limestone rock. This neutralises the pH and removes iron without the use of energy or costly technologies. Depending on the metal concentration and type, as well as pH, a variety of rock types are used to neutralise acid and precipitate metals. Such acid mine drainage retention ponds were built using 1 m thick limestone layers (Hedin 2020). Other ponds were built using thick layers of gravel plus amendments. HUESKER along with an international consultancy to were engaged to create a vertical flow pond covered with an active geocomposite for an abandoned nickel mine in Finland. In the design, a thin layer of highly active cation adsorbent replaces the thick layer of limestone or gravel. The granular adsorbent is mechanically stabilised and fixed between two layers of geotextile and can therefore be installed with a constant layer thickness. Due to the large surface area of the adsorbent, the thin layer of the active geocomposite has higher efficiency for water treatment than a thick layer of stone. The simplified installation process of the geocomposite speeds up construction time for large-scale filter ponds. In August 2021, a pilot field was built in Finland to prove the application’s long-term efficiency. Once a week, water samples are collected and analysed in the laboratory. The samples from the first three months show a reduction of nickel by an average of 65%, and copper as well as aluminium by an average of more than 90%. In addition, the reduction of other metals and the pH value are documented. This presentation introduces the concept of vertical flow ponds covered with active geocomposites and discusses all findings from the pilot plant in Finland.

Keywords: active geocomposites, acid mine drainage, water treatment, innovative geosynthetic products

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