The electro-winning system [SX-EW] of extracting copper is a step in the right direction as the mining industry attempts to develop methods that have less of an impact on the environment. Really, it's a huge step since it eliminates tailings impoundments, which are unsightly and can cause water pollution, and smelting, which can cause soil and air pollution. Howver, SX-EW only works on oxide ore, whereas the majority of the ore at Rosemont is sulfide and will not dissolve into solution in a reasonable period of time. Therefore, leaching can be used on some 14% of the ore, or approximately 59 million tons over some 15 years. Sulfuric acid, the leaching agent, is brought on site in large tankers. The sulfuric acid is diluted and sprayed or dripped over oxide ore, which dissolves the oxidized minerals completely in the solution. The solution, “pregnant” with the dissolved metals, is then piped to the SX-EW plant. The waste solution is piped to on-site holding ponds, which are securely lined, awaiting the next load of oxide ore to be placed on the leach pads.
Sulfuric Acid Tanker on mining site Pads for Leaching Ore with Sulfuric Acid Solution Ideally, this system is a closed circuit and is considered environmentally safe. However, there are two conduits to environmental impact. First, the leach solution is stored in open ponds (until the mine is closed then it is put in barrels and taken to toxic waste dumps). Second, spills of the sulfuric acid and the leach solution, which is laden with heavy metals, including radionuclides that are present with metals in Arizona, can spill as they are piped around the facility. 1) Toxic Ponds: As the leach solution is reused, the unwanted metals concentrate into a very toxic solution, which sits out in open ponds, waiting to be piped back to be sprayed or dripped onto fresh ore on the leach pads. Holding Ponds for Leaching Solution for Leach Pads (on far right) Close-up of Holding Pond with Leach Solution The data on the table below shows the "Characteristics of Leach Solution, which is classifed as hazardous waste. Whereas these ponds are an inevitable part of mining and are considered to be an improvement over tailings impoundments and smelting, it is questionable if they are appropriate for a National Forest setting with its requirements for beneficial use.
As called out in the Rosemont Plan, Augusta is well aware of the problem of "accidents" and "incidents," which they cannot and do not guarantee will not occur.
Summary of Spills at Sierrita Copper mine, Pima County, Arizona —All spills were on-site in mill area 9/06/05 8,058 lbs. Sulfuric Acid (Report) 2/5/02 39,375 gals. Sulfuric Acid 7/3/01 1,209 lbs. Sulfuric Acid 5/22/00 5,350 gals. Leach Solution (Sulfuric acid/Copper) 5/05/98 40,000 gals. Leach Solution (Sulfuric acid/Copper) 5/04/98 120,000 gals. Leach Solution (Sulfuric acid/Copper) 3/29/97 8,000 lbs. Sulfuric acid-93% 7/11/97 2,798 lbs. Sulfuric acid 8/11/96 100 gals. Sulfuric acid 6/12/96 13,263 lbs. Leach Solution (spent electrolyte) 3/23/96 3,000 lbs. Sulfuric acid 1/10/96 2,000 lbs. Sulfuric acid 12/19/94 5,000 gals. Leach Solution For Documentation of Spills, See Hazardous Material Incidents--Sierrita The Hazardous Waste Incidents at Bagdad mine are of particular interest for a proposed mine that will need to truck in various chemicals and truck out copper concentrate to a smelter. These spills of extremely toxic chemicals and copper concentrate seriously impact the roadways and soils, as well as potentially pollute ground or surface water, on Forest Service, BLM and State Trust Land. Apparently, there was a winding road to the railroad junction, and eventually another route was used. 12/07/04 7,484 lbs. Leach Solution On-site (Report) 9/10/04 354 gals. Sulfuric Acid On-site (Report) 12/04/00 <200 gals. Sulfuric Acid State Trust 9/18/00 5,850 gals. Xanthate Federal 3/11/99 misc Cyanides, Acids Federal 3/07/99 12,000 gals. Effluent (treated ww) Federal 3/01/99 200 gals. Sulfuric Acid State 7/27/98 ? Sulfuric Acid State 1/01/98 50,000 lbs. Copper Concentrate State 12/12/97 40,000 lbs. Copper Concentrate State 9/17/97 7/7200 lbs. Sulfuric Acid On-site 6/11/97 50,000 lbs. Copper Concentrate Bagdad town 3/09/97 1,500 lbs. Sulfuric Acid On-site 7/18/96 3.57 lbs. Mercury Bagdad town 6/18/96 3/40,000 lbs. Copper Concentrate State/Private 8/31/95 35,000 lbs. Copper Concentrate State 7/21/95 48,100 lbs. Lead Sulfide/Cu Conc. County 11/22/94 2,100 gals. Diesel County 3/02/94 60 gals. Sulfuric Acid State 6/11/93 600 gals. Sulfuric Acid State 5/26/93 200 gals. Diesel Private prop 2/22/92 1,200 gals. Sulfuric Acid On-site 5/09/91 ? Sodium Cyanide State 9/18/90 13 gals. PCB On-site 12/17/87 1,500 gals. Sulfuric Acid State 11/09/87 2/2,500 gals. Sulfuric Acid State 9/20/86 50-60 gals. Sulfuric Acid State For Documentation of Spills, See Hazardous Material Incidents--Bagdad How Sulfuric Acid Spills Impacted Public Supply Water Wells
The sudden increases, then lowering of the levels, are not indicative of a traditional sulfate plume, or of a testing abnormality. The problem in analyzing the data was finding the time frame that the sulfuric acid would flow from the spill in the mill/leach area to the public supply wells. I finally found the magic number! It takes 39 months. Of six correlations available, four in a row were 39 months, then 24 months, then 21 months. It could be expected that with time the spills make a path to make the trip faster. Date correlation of Sulfuric Acid Spills and Spikes in Sulfates
* These are approximate because Community Water was only testing semi-annually during part of this period. Click here to go to Community Water Data
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