Mercury Management in Modern Precious Metals Mines

1. Mercury Management in Modern Precious Metals Mines Glenn Miller and Greg Jones Department of Natural Resources and Environmental Science University of Nevada, Reno

2. Purpose of the Study • Determine the total amount of byproduct mercury produced and how it is managed • Determine and analyze the atmospheric emissions both from the Toxic Release Inventory and the Voluntary Mercury Reduction Program in Nevada

3. Historic Use of Mercury in Precious Metals Mines • Gold will dissolve in liquid mercury and this process was extensively used for recovery of gold from ground ore • Generally utilized plates covered with mercury to which an ore slurry was passed over • Estimated 1 lb of mercury lost for each ton of ore processed (Comstock) • Tailings often eroded into streams or were deposited directly into streams • Metallic mercury converted to ionic mercury and then methylated to make the toxic methyl mercury

4. Mercury Legacy from Historic Mines • Elevated concentrations of mercury in sediments • Elevated concentrations of mercury in fish, birds and other wildlife (Lahontan, Carson sink, Walker Lake, Sierra Nevada streams and others) • Restrictions on the amount of fish that should be consumed by humans

5. Toxic Issues with Mercury • Neurotoxicity • Birth defects • Kidney function

6. Current Gold Mines • Mercury is not used to extract gold or silver in Nevada mines (although still in developing countries) • Mercury release to the environment is related to the co-incidence of mercury in many gold ores in Nevada, and release during ore processing • Mercury is produced as a byproduct from gold mines in Nevada, and is the largest source of new mercury in the U.S.

7. Byproduct Mercury Production The Chemistry Au + O2 + CN- Au(CN)2- (water soluble) Hg + O2 + CN- Hg(CN)2 + Hg(CN)42- (water soluble) Both the gold and mercury cyanide complexes are trapped on carbon and recovered during processing Mercury is distilled (retorted) from the gold and collected as liquid mercury and sold by the flask (76 lbs)

8. Previous records for Hg Productionfrom the Nevada Division of Minerals

9. Total Mercury By-Product Recovered for Sale (pounds and metric tons) (provided by each company) *total Newmont byprodut (Nev. Div. Of Minerals)

10. How is Byproduct Managed • Sold or transferred to three primary mercury recyclers • Bethlehem Apparatus Co. Inc., Hellertown, PA;. • D.F Goldsmith Chemical and Metal Corp, Evanston, IL • Mercury Waste Solutions, Inc., Mankato, MN • Each of these companies is regulated by the EPA • Current U.S. demand for mercury is 150-200 tons/year; Hg produced in NV is 30-50 tons • Price of Hg increased over the past three years from $150/flask to approx. $750/flask • Management and transfer is conducted in a safe and reliable manner • There is no requirement for supplying data to the public on mercury sales

11. Atmospheric Emissions of Mercury from Precious Metals Mines in the U.S. • Generally not measured until 1998 • Toxics Release Inventory was applied to precious metals mines • Revealed that precious metals mines were some of the single largest sources of atmospheric mercury in the U.S. • Voluntary Mercury Reduction Program (VMRP) initiated in 2001

12. Mercury Air Emissions (lbs) from Precious Metals Mines, 1998-2003 (TRI data)

13. Ranking of States for Atmospheric Mercury Release NV Mines 2003 (est) 4500 lbs

14. Atmospheric Mercury Releases • Nevada was the #2 state nationally in mercury release in 1998 (after Texas) and dropped to #7 or #8 in 2003 and reduced its atmospheric emissions by 2/3 • Nevada still is the second largest source of atmospheric mercury west of the Mississippi (again after Texas)

15. VMRP Data from Jerritt Canyon (2001-2003)

16. VMRP Data from Barrick Goldstrike

17. Value of production up by 11% from 2002 due to higher price Top 7 years of all time 7.3 M oz in 2003, 82% of U.S. and 9% of world production

18. Estimate of Total Amount of Mercury Emitted from Nevada Mines, 1980-present • Assume an average of 12,000 pounds per year from 1988-2001 (inclusive), and 5000 pounds for 2002 to 2004 (inclusive), and ignore the years 1980-1988. • 12000 x 14 = 168,000 lbs • 5000 x 3 = 15,000 lbs • Total is 183,000 lbs or 83 metric tons (70-100 tons) • Contributions of Hycroft, Paradise Peak and Hog ranch are unknown

19. What is the Significance of this Mercury Release • Largely unknown, although it is much less than the estimated 6000-7000 metric tons released into the Carson River drainage • Transport of mercury is still not well understood, although the areas around the sources will receive the greatest amount of fallout • It is unclear if the elevated mercury in Idaho fish is related to mercury releases from the mines

20. 23 major gold mines (8 not on the Carlin trend with > 100 K oz production)

21. Conclusions • Management of byproduct mercury • Byproduct mercury appears to be managed well • Based on discussions with the recyclers, they feel strongly that a demand for mercury in the U.S. exists and byproduct mercury can be used to satisfy this need, primarily in lights and electrical equipment • There is currently no legal method for reducing liability to the mining industry for storing mercury, while selling it into commerce eliminates the liability • No need for any changes

22. Conclusions • Atmospheric release of mercury • The gold mining industry previously was a major source of mercury release to the atmosphere • Through the VMRP and other efforts by the industry, a 2/3 reduction has been realized, although mining sites still are some of the highest point sources • Further reductions can be realized with current technology

23. Recommendations • Atmospheric mercury emissions from mines should be regulated by either the State or EPA. While successful, the VMRP remains voluntary, and does not require new sources to participate. • More consistent and more mercury measurements should be required. Because of the complexity of the mercury emission sources, a systematic evaluation of the methods used to determine mercury emissions rates and concentrations should be undertaken.

24. Recommendations (2) • New systems for better mass balance are recommended for accurate assessments of mercury release. This includes more precise measurements of mercury in the ore, mercury in the process fluids, and mercury sent out to the tailings facilities. The amount of mercury in the ore should be accounted for in a life-cycle assessment. • Byproduct mercury production and sales should be reported • Fate studies for the mercury deposition need to be expanded. Is the mercury deposition regional or continental, or global? Who has the burden of showing where the mercury goes?