Anna Tornivaara, Geological Survey of Finland, P.O. Box 1237, FI-70211 FINLAND, e-mail: anna.tornivaara(at)gtk.fi
The most important environmental priorities in the mining sector today are reducing waste production, reusing and recycling wastes, and preventing acid mine drainage. In the segregation technique (which is also referred to as selective handling or sorting) waste fractions are separated based on their environmental characteristics with the aim of decreasing the amount of acid producing or hazardous waste that requires final disposal at the site. This will reduce the areal coverage of potential environmental impacts and can also reduce the need for construction materials. These measures lead to savings in construction costs because the requirements for non-acid producing waste are not as strict as for hazardous waste. Segregation also opens up better opportunities for recycling and reusing of (non-acid producing) waste materials by removing the environmentally problematic part of the waste.
Description of the method
In the segregation process, waste is physically sorted prior to disposal into, for example, non-acid generating (NAG) and acid generating (PAG) waste fractions, which will be disposed of in separate waste areas (MEND 2001). Segregation does not prevent ARD although it limits the amount of possible ARD generating waste. It also increases waste management efficiency by creating isolated target areas to which ARD reduction measures can be directed [e.g. the use of completely saturated impoundments to minimize waste material exposure to air, or methods to minimize surface and groundwater contact with PAG materials while maximizing contact with alkaline materials (INAP 2009). Segregation is especially suitable for tailings materials (Kauppila et al. 2013).
In the mining sector, segregation of ore and waste is a standard practice, while similar techniques can also be utilized for the separation of different waste materials. It is applied e.g. at the Aitik Cu mine in Sweden to descrease the amounts of acid producing waste rocks.
- Non-acid generating material can be used at a mine site for construction material
- Reuse and recycling is easier when waste materials are more homogeneous
- Less PAG material means savings in construction and handling costs [e.g. amount of basal structure material (MEND 2001, INAP 2009)]
- Segregation can be more time consuming
- Possible for some extra costs due to separate handling, testing and monitoring
- Identification of materials for segregation requires constant monitoring by qualified personnel, need for labour force
- Possibly requires temporary disposal areas (MEND 2001, INAP 2009)
To make the method profitable from both an economical and environmental point of view, there must be enough chemically distinct material (e.g. PAG and NAG waste) to warrant segregation.
The materials and maintenance needs for segregation are typical for those of normal waste handling (e.g. vehicles, equipment).
Site specific data needs
Segregation criteria should be well identified to minimize errors and the need for re-handling. Before handling, transport, and deposition, waste management and operational monitoring programs should be established to identify and segregate materials (INAP 2009). The mine waste plan should be based on detailed waste characterization and appropriate modelling. Special handling requirements should be investigated and waste facility design should be taken into account to provide isolation and proper sealing of PAG during storage (e.g. to inhibit water infiltration and oxygen transfer to the material) (INAP 2009).
Requirements for the materials and appliances
Measures should be taken to isolate and neutralize the segregated PAG component of waste. For instance, the acid producing material can be capped with a layer of low permeability material, and then with NAG material and topsoil to reduce water and air movement into the reactive rock (INAP 2009).
Minimisation / treatment of potential discharges
Broad waste characterisation and regular sampling and testing programmes (before and after segregation) are the key factors for successful waste disposal.
Monitoring / control needs
Normal and ongoing monitoring is required, especially in the disposal facility for acid generating material.
INAP 2009. The GARDGuide. The Global Acid Rock Drainage Guide. The International Network for Acid Prevention (INAP). http://www.gardguide.com/ modified 2014. Read 17.7.2014.
Kauppila, P., Räisänen, M.L. & Myllyoja, S. (Eds) 2013. Best environmental practices in metal mining operations. The Finnish Environment 29en/2011, Environmental Protection, Finnish Environment Institute (SYKE). The publication in English is available only on the internet: www.syke.fi/publications (available also in Finnish). 219 p.
MEND 2001. Mine Environment Neutral Drainage Program. Prevention and Control. Volume 4. Manual 5.4.2d. G.A. Tremblay and C.M. Hogan (Eds.), CANMET