NAG test with leachate analysis
Teemu Karlsson, Geological Survey of Finland, P.O. BOX 1237, FI-70211 Kuopio, FINLAND, e-mail: teemu.karlsson(at)gtk.fi
Prediction of the leachability of contaminants from mine wastes is required to assess the environmental impacts and to design proper waste and water management systems. Besides providing information on acid generation potential, the leachate analysis of the NAG test solution can be utilized to assess potential release of metals, metalloids and salts from the mine waste sample after complete sulphide weathering (Barnes et al. 2015).
The NAG test leachate data in assessment of water quality for mine waste sites has not been commonly used, which may be due to the lack of reliable empirical database comparing kinetic test or field results and mass release from standard NAG test (Barnes et al. 2015)
The NAG test determines (i) the solute release attributed to sulphide oxidation by hydrogen peroxide (H2O2), and (ii) the solubility of the solutes at the pH of the final NAG solution. Therefore this method has promising potential for use in rapid prediction of long-term seepage quality. (Barnes et al. 2015)
Description of the method
During the basic NAG procedure a portion of NAG extract is separated before titration by pipette to analyse elements solubilised during the sulphide oxidation with peroxide. Element concentrations are then determined from the extract e.g. by ICP-OES/MS. The extract contents produced by the NAG test can be used in assessing contaminant mobility during long-term acid generating reactions. (Räisänen et al. 2010, Barnes et al. 2015) For general information about the NAG test, see Net Acid Generation (NAG).
The NAG test with leachate analysis can be used to determine total potential loading of metals under acidic conditions after complete oxidation of reactive sulphides, supplementing e.g. time consuming kinetic humidity cell tests (INAP 2009, Barnes et al. 2015).
Advantages (INAP 2009, Rutkowski et al. 2010, Barnes et al. 2015)
- Simulates the conditions of complete sulphide oxidation and provides information about the worst-case effluent.
Disadvantages (INAP 2009, Rutkowski et al. 2010, Barnes et al. 2015)
- Instantaneous oxidations of sulphides, in field conditions reaction kinetics are more complicated and occur over a longer time period.
- Sulphides may be oxidized incompletely, due to the decomposition of H2O2 during the test
Not used systematically.
Barnes, A., Bowell, R., Warrender, R., Sapsford, D., Sexsmith, K. Charles, J., Declercq, J., Santonastaso, M. & Dey, B. 2015. Comparison between Long-Term Humidity Cell Testing and Static Net Acid Generation (NAG) Tests: Potential for NAG Use in Preliminary Mine Site Water Quality Predictions. In: Brown, A., Bucknam, C., Carballo, M., Castendyk, D., Figueroa, L, Kirk, L., McLemore, V., McPhee, J., o´Kane, M., Seal, R., Wiertz, J., Williams, D., Wilson, W. & Wolkersdorfer, C. (Eds) 10th International Conference on Acid Rock Drainage & IMWA Annual Conference. pp. 1-10.
INAP 2009. The GARD Guide. The Global Acid Rock Drainage Guide. The International Network for Acid Prevention (INAP). http://www.gardguide.com/
Räisänen, M.L., Kauppila, P.M. & Myöhänen, T. 2010. Suitability of static tests for acid rock drainage assessment of mine waste rock. Bulletin of the Geological Society of Finland, Vol. 82, 2010, p. 101-111.
Rutkowski, T., Waples, J., Gusek, J. & Shipley, B. 2010. Biochemical reactor media characterization study. National Meeting of the American Society of Mining and Reclamation (ASMR), Pittsburgh, PA, “Bridging Reclamation, Science and the Community” June 5-11, 2010, Conference Proceedings p. 888-913.