Presentation is loading. Please wait.

Presentation is loading. Please wait.

A review of sources and sinks for nitrate in the mining environment Christopher H. Gammons, Ph.D. Professor, Dept. of Geological Engineering Montana Tech.

Similar presentations


Presentation on theme: "A review of sources and sinks for nitrate in the mining environment Christopher H. Gammons, Ph.D. Professor, Dept. of Geological Engineering Montana Tech."— Presentation transcript:

1 A review of sources and sinks for nitrate in the mining environment Christopher H. Gammons, Ph.D. Professor, Dept. of Geological Engineering Montana Tech Butte, Montana

2 Acknowledgements This research was supported by Goldcorp Inc. Thanks to mines and agencies who supplied data and photographs

3 Sources of nitrate in mine settings Explosives Cyanide breakdown Sewage Atmospheric deposition Geological background Mine-related Non-mine-related

4 Explosives ANFO – 96% ammonium-nitrate, 4% fuel oil – Both ammonium and nitrate are highly soluble in water – Very little residual nitrate if explosives are handled carefully and combustion is complete Emulsions, gels – Also contain ammonium-nitrate, but mixture is contained in a gel or slurry that minimizes contact with water – Leach slower, but over time will also release nitrate and ammonium

5 Nitrate concentrations in mine waters from blasting range: 10 mg/L (NO 3 -N) Depends on many factors, including: -Blasting efficiency (% detonation) -How much precipitation on site -Contact time of water with mine waste -Evapoconcentration effects (ponds and lakes) -Presence/absence of algae/aquatic plants Ammonium concentrations can also be high, but over time ammonium will oxidize to nitrate

6 Breakdown of cyanide CN - OCN - SCN - NH HCO 3 - NO 3 - cyanide cyanate thiocyanate ammonium nitrate NO 2 - SO 4 2- HCN NOx(g) in air VOLATILIZATION OXIDATION pH < 9

7 Breakdown of cyanide CN - OCN - SCN - NH HCO 3 - NO 3 - cyanide cyanate thiocyanate ammonium nitrate NO 2 - SO 4 2- HCN NOx(g) in air VOLATILIZATION OXIDATION pH < 9

8 Breakdown of cyanate OCN - + 2H 2 O → NH 3 + HCO 3 - SCN - + 2H 2 O + 2O 2 → SO CO 2 + NH 4 + Breakdown of thiocyanate Both pathways generate ammonium

9 pHtotal CNWAD CNSCN-OCN-NO3-NNO2-NNH3+NH4 PINBC S PINAC S PINBAR S PINMBC S PINMAC S PINRCLSM S LTFL2 S LTFL3 S LTFL7 S < LTBC S LTAC S LTBAR S LTP1/2 S LTLG S LTDP S LTFL2 O LTFL3 O LTFL7 O LTBC J LTAC J LTBAR J Concentrations (mg/L) of cyanide and cyanide breakdown products from gold mines in Nevada (from Johnson et al., 2000).

10 Removal (sinks) of nutrients from mine water Many technologies exist for removal of nutrients from treated sewage In theory, these same technologies can be used for mine waters PROBLEMS Massive volumes of water – e.g., tailings ponds, pit lakes Low organic carbon in source Remote settings, extreme climate Cost

11 Treatment Relative cost Time to desired result Comments Natural attenuation Very lowVery long (decades?) May be a reasonable approach if there is no likelihood of discharge to receiving surface water and groundwater. For pit lakes, may need artificial mixing to accelerate oxidative processes. Example: Colomac Mine. Enhanced natural attenuation LowLong (several years) Addition of limiting nutrient (usually P) to a water body may stimulate oxidative or reductive processes that remove N-compounds. Example: Colomac Mine. Land application Low- medium n/aNeed to monitor carefully for contaminated groundwater. Some compounds may be toxic to plants (thiocyanate?). Example: Beal Mine. Constructed wetlands: aerobic MediummonthsLarge, shallow ponds remove nutrients through assimilation. May need to harvest plant mass. Evaporation. Possible impacts to aquatic life. Example: Warm Springs Ponds, Montana. Nitrate: Treatment alternatives

12 Treatment Relative cost Time to desired result Comments Constructed wetlands: anaerobic Medium1-2 year startup time May be effective for low-cost removal of low- level COCs. Not feasible for high concentrations or high flows. Sensitive to climate extremes and changes to source water chemistry. May clog up. Permeable reactive barrier Medium1-2 year startup time Used to remove COC’s from groundwater in situ. Longevity uncertain. May clog up. Reactive material may become coated. Bioreactors High1-2 year startup time Effective at removal of nitrate by denitrification. Sensitive to changes in source water chemistry. Example: Landusky Mine. Ion Exchange HighimmediateRobust technology, but expensive. Effective for some COCs but not others. Column regeneration creates waste. Reverse osmosis Very HighimmediateRobust technology, but expensive. Lowers concentration of multiple COCs simultaneously. Creates brine waste that must be disposed. Nitrate: Treatment alternatives (cont.)

13 Some Examples 1)Butte, Montana 2) Landusky, Montana 3) Stillwater, Montana

14 1. Butte Berkeley Pit lake pH 2.6 Very high dissolved metals No nitrate! Flooded underground workings pH 4 to 7 Low to high dissolved metals No nitrate!

15 Why no nitrate in Butte mine waters? All of these waters are anoxic All of these waters are in contact with pyrite Conclude: pyrite catalyzes denitrification (but only in anoxic waters): 5FeS NO H + → 7N 2 + 5Fe SO H 2 O (Plenty of published literature on this)

16 2000: Note very large cyanide heap leach pad in upper left Slides courtesy of David Williams, Butte BLM Example 2: Zortman-Landusky, Montana

17 Sept (mg/L) L87 & L91 Pad influent BR-3 Outflow Potential ARAR limit Nitrate < 110 Selenium CN (wad) na CN (total) Landusky leach pad treatment system three bioreactors In series Avg. flow ~ 285 L/min

18 Bioreactor performance At first, great. Denitrifying bacteria NO 3 → N 2 More recently, having problems with removal efficiency due to: – Changes in leach pad water chemistry Drop in pH from neutral to around 4 Increase in nitrate-N from 200 to > 300 mg/L – Buildup of “organic sludge” in the bioreactors State is exploring options

19 Example 3: Stillwater Mine, Montana Large underground platinum-palladium mine High nitrate (20 to 40 mg/L as N) in mine waters from blasting residues

20 Treatment scheme Need to treat gallons/minute – 15 to 50 kg N per day Biological treatment – Moving Bed Bioreactors (MBBR) – Anaerobic/Aerobic – Add methanol, SRP Land Application – Irrigated pasture Land Application site

21 Moving Bed Bioreactors (MBBR) at Stillwater Empty Full Photo courtesy Stillwater Mining

22 Stillwater Mine: Summary Performance has been very good for > 5 years Optimal temperature ~ 15-20°C Some problems in winter when water temperature drops below 10°C – Need a heater to keep the MBBR cells warm

23 Summary N-contamination is a significant problem for the mining industry for which there is very little published information N- and CN-chemistry is complicated There are multiple physical, chemical, biological pathways Some of these pathways can be used to a mine’s advantage to minimize later N-impacts

24 Some references Akcil, A., and Mudder, T. (2003) Microbial destruction of cyanide wastes in gold mining: process review. Biotechnology Letters, 25(6), Chapman J.T., Coedy W., Schultz S., Rykaart M. (2007) Water treatment and management during the closure of the Colomac Mine. Proc. Mine Closure 2007 Conference, Santiago, Chile. Ferguson, K.D., and Leask, S.M. (1988) The Export of Nutrients from Surface Coal Mines, Environment Canada Regional Program Report 87-12, March, 1988, 127 p. Forsyth B., Cameron A., Miller S. (1995) Explosives and water quality. Proc. of Sudbury 1995, Vol. 95, Koren, D. W., Gould, W. D., and Bedard, P. (2000) Biological removal of ammonia and nitrate from simulated mine and mill effluents. Hydrometallurgy, 56(2), Morin K. A. and Hutt N.M. (2009) Mine-water leaching of nitrogen species from explosive residues. Proc. GeoHalifax Revey, G.F. (1996) Practical methods to control explosives losses and reduce ammonia and nitrate levels in mine water. Mining Engineering, July, p

25 Questions?

26 ANFO Stable isotope composition of different forms of nitrate


Download ppt "A review of sources and sinks for nitrate in the mining environment Christopher H. Gammons, Ph.D. Professor, Dept. of Geological Engineering Montana Tech."

Similar presentations


Ads by Google