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

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

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 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 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) Estimated 1 lb of mercury lost for each ton of ore processed (Comstock) Tailings often eroded into streams or were deposited directly into streams 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 Metallic mercury converted to ionic mercury and then methylated to make the toxic methyl mercury

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

Toxic Issues with Mercury Neurotoxicity Birth defects Kidney function

Current Gold Mines Mercury is not used to extract gold or silver in Nevada mines (although still in developing countries) 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 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. Mercury is produced as a byproduct from gold mines in Nevada, and is the largest source of new mercury in the U.S.

Byproduct Mercury Production The Chemistry Au + O 2 + CN - Au(CN) 2 - (water soluble) Hg + O 2 + CN - Hg(CN) 2 + Hg(CN) 4 2- (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)

Previous records for Hg Production from the Nevada Division of Minerals Mine Hycroft ParadisePeak Newmont Borealis1824 Hog Ranch McDermitt (primary Hg mine)

Total Mercury By-Product Recovered for Sale (pounds and metric tons) (provided by each company) Jerritt Canyon Placer Dome Barrick Newmont E * Newmont W Total Pounds Metric Tons * total Newmont byprodut (Nev. Div. Of Minerals)

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

Atmospheric Emissions of Mercury from Precious Metals Mines in the U.S. Generally not measured until 1998 Generally not measured until 1998 Toxics Release Inventory was applied to precious metals mines 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. 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 Voluntary Mercury Reduction Program (VMRP) initiated in 2001

Mercury Air Emissions (lbs) from Precious Metals Mines, (TRI data) Goldstrike Pipeline Jerritt Canyon Newmont Carlin (S) Twin Creeks Total from NV Mines (est) Total all NV Industries

Rank (2002) StatePounds released (2001) Pounds released (2002) 1Texas 14,76614,505 2Ohio 11,4059,625 3Pennsylvania 9,0899,177 4Nevada 12,9599,069 5Indiana 7,1687,645 6Illinois 5,9635,610 7Alabama 5,9034,729 8North Carolina 4,1644,507 9California 5,6684,173 10West Virginia 6,2824,051 11Kentucky 5,2563,670 Ranking of States for Atmospheric Mercury Release NV Mines 2003 (est) 4500 lbs

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 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) Nevada still is the second largest source of atmospheric mercury west of the Mississippi (again after Texas)

SourceEmissions (2001) (Baseline) Emissions (2002) Emissions (2003) Carbon regeneration kilns Venturi mercury wet scrubbing/carbon polishing system installed in March Refinery (included above) Emissions routed to carbon regeneration kiln control system in September Roaster west Sodium hypochlorite injection system installed in September, 2002 Roaster east Sodium hypochlorite injection system installed in September, 2002 Total VMRP Data from Jerritt Canyon ( )

SourceEmissions (2001) (Baseline) Emissions (2002) Emissions (2003) Retorts 1,2,3 11 Mill furnace 1, Carbon column added Electrowinning cell 613 Included above Emissions sent through mill furnace carbon column Carbon kiln Autoclave circuit 548 Roaster Total VMRP Data from Barrick Goldstrike

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

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

What is the Significance of this Mercury Release Largely unknown, although it is much less than the estimated metric tons released into the Carson River drainage Largely unknown, although it is much less than the estimated 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 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 It is unclear if the elevated mercury in Idaho fish is related to mercury releases from the mines

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

Conclusions 1. Management of byproduct mercury Byproduct mercury appears to be managed wellByproduct 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 equipmentBased 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 liabilityThere 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 changesNo need for any changes

Conclusions 2. Atmospheric release of mercury The gold mining industry previously was a major source of mercury release to the atmosphereThe 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 sourcesThrough 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 technologyFurther reductions can be realized with current technology

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. 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. 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.

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. 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 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? 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?