Solubility of harmful substances, leaching methods

Päivi M. Kauppila¹ & Henna Punkkinen², ¹Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND, e-mail: paivi.kauppila(at)gtk.fi ; ²VTT Technical Research Centre of Finland, P.O. Box 1000, FI-02044 VTT, Finland

Mine wastes contain various elements and compounds that may be harmful to the environment. These compounds may be metals (e.g. Al, Cr, Cu, Fe, Mn, Mo, Pb, Ni, Zn, V), metalloids (As, Sb), salts (e.g. sulphates), nutrients (nitrogen compounds) or organic compounds. They originate in the deposit itself or from the explosives used in the excavation (nitrogen compounds), process chemicals (e.g. xanthates, cyanide, sulphur compounds, salts) or the fuels used in machines and equipment (mineral-based oils). The occurrence and concentrations of harmful metals, semimetals, sulphates and nutrients depend primarily on the geology and mineralogy of the ore deposit as well as the efficiency of the concentrating process (Kauppila et al. 2013). The leachability of potentially harmful constituents varies strongly for each waste type and each element. Therefore, leaching tests are needed to evaluate whether these elements or compounds are prone to mobilize from the mine waste (e.g. Technical Comittee 2012).

There is a wide variety of leaching tests available to evaluate leaching of potential contaminants from mine wastes. These tests range from short-term compliance tests to long-term laboratory and field tests. The most commonly used tests for mine wastes include column leaching test (CEN/TS 14405:2004), humidity cell test and sequential extractions. Field tests are currently gaining more interest and popularity, as they correspond to the actual disposal conditions of the waste but in smaller scale.

1. Short term tests / compliance tests

• Batch extraction tests
• Column leaching test
• pH-dependence leaching test
• Compliance test for leaching of granular materials and sludge
• Selective extractions
• NAG test with leachate analysis
• Synthetic precipitation leaching procedure (SPLP)
• Meteoric water mobility procedure (MWMP)
• California waste extraction test (WET)
• Modified test for shake extraction of solid waste with water
• British Columbia special waste extraction procedure (BC SWEP)
• Leaching toxicity of solid wastes
• Dynamic monolith leaching test
• Compacted granular leaching test
• Sulphidic metals

2. Methods for the long-term prediction

A. Long term leach-tests

• Humidity cell test
• Column test

B. Chemical extractions

• Selective extractions
• Sequential extraction

C. Field tests (see also Field investigations)

• Simulated rainfall leach tests
• Pilot scale tests in field conditions
• Field scale investigation and lysimeter studies
• Wall washing
• US Geological Survey field leach test (FLT)
• Field cells / test pads / mine facilities

3. Chemical analysis of process water from concentration tests

References

CEN/TS 14405: Characterization of waste – Leaching behaviour tests – Upflow percolation test

Kauppila, P., Räisänen, M.L. & Myllyoja, S. (eds) 2013. Best Environmental Practices in Metal Ore Mining. Finnish Environment Institute 29en / 2011. 219 p. https://helda.helsinki.fi/handle/10138/40006

Technical Committee 2012. Technical Committee CEN/TC 292 2012. Characterization of waste – Overall guidance document for characterization of wastes from extractive industries. CEN/TR 16376:2012.