Wastes and waste facilities

Päivi M. Kauppila, Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, FINLAND, e-mail: paivi.kauppila(at)gtk.fi

Mining and ore processing produces several different types of mining waste that require recycling or safe disposal and handling. Typical mining wastes include waste rock from excavations, overburden removed in construction and mining preparations, tailings from mineral processing, and sludges from water treatment. Their characteristics and composition depend particularly on the geology and mineralogy of the exploited ore deposit and the techniques and chemicals used in ore processing and in water treatment (sludges).

To minimise the amount of waste requiring final disposal and to decrease the footprint of mining, it is optimal to utilise as much of the waste materials as possible during the operative phase of the mining. Mining waste can often be used e.g. in earth construction at the mine site or elsewhere, landscaping, as a backfill in mining voids or as a raw material e.g. for cement or bricks, or exploitable wastes can be stored separately at the mine site for later use in mine site rehabilitation. With detailed characterisation and evaluation of the exploitation potential and by adapting the ore processing circuit, it can be possible to increase the amount of products produced from the ore deposit and to decrease the amount of disposed waste. In addition, new re-use and reprocessing technologies are nowadays available to create beneficial products from problematic mine wastes. However, in many cases the geotechnical or environmental characteristics of the wastes prevent their further use and long-term disposal is required.

Mining waste may cause effluents to water and dust or gas emissions. The degree of harmfulness of these emissions depends on the characteristics of the waste materials. Particularly, if the excavated ore contains sulphide minerals, low quality mine drainage may be a notable environmental concern. In addition, waste containing uranium or other radioactive nuclides are prone to produce radon emissions. To predict the quality and amount of emissions and to select optimal waste management systems, careful characterisation of the wastes is required before any decisions on the waste management are made. Characterisation should include measurements of chemical and mineralogical composition and geotechnical properties as well as evaluation of the long-term behaviour of waste, particularly the potential to produce mining influenced waters (i.e. acid mine drainage or neutral mine drainage).

Based on characterisation, adequate waste management systems are designed. The management starts from the selection of sufficient basal and dam structures for the waste facilities. Variety of options is available from the use of natural soil layers of the site to more complex synthetic multilayer structures. During production phase, management techniques include various waste disposal techniques such as blending and layering, raising of dams, use as a backfill in mining voids and treatment of water effluents of the wastes. The decisions made before and during the mining operations form the basis for the applicable technologies required in mine closure.

After mine closure, the ultimate objective for the management of the waste facilities is to minimise long-term environmental impacts. Depending on the characteristics of the waste materials, the measures can include different covers from simple one layer soil covers to multilayer synthetic structures, backfilling in mining voids, landscaping and/or adding vegetation. In many cases, the treatment of drainage waters is still required after closure. It can be made using passive or active water treatment techniques.

Figure 1. Disposal of tailings at a talc mine in Finland (Photo © P. Kauppila, GTK)

More detailed descriptions of the objectives of mine waste management, methods used in waste characterizations and suitable closure tehnhologies for waste facilities are presented in the pages below. Case studies introducing site-specific information on the exploitation and performance of different closure technologies are also provided. Research and development chapter furhter presents research made during Closedure project related to laboratory tests methods on cover systems and on the applicability of chemical characterization methods to evaluate seepage water quality.