I don't think they like cyanide very well.
Cyanide Spring
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by Philip M. Hocker
GOLD GOES BOOM:
A canoe made of gold is too soft to run over rocks and too heavy to portage well. Gold makes lousy pitons and carabiners for climbing. Did you ever hear of a gold- filled sleeping bag?
Nevertheless, it appeals to some people. That appeal is driving a new gold rush around the world. The rush raised the annual rate of world gold production from 31 million ounces in 1980 to 44 million in 1987, and is still accelerating.
The increase in the United States has been even more dramatic, from one million ounces mined in 1980 to five million in 1987, still rising to seven and a half million ounces in 1989.
Nevada is the heart of this rush, as host to fully half of U.S. gold production, and the impacts are massive in California, Montana, and Colorado. Utah and Washington are active. New mines are planned in eastern Oregon, where a surge last fall led to tens of thousands of new claim filings. In South Carolina one of the largest tailings impoundments in the country has just been completed for newly-opened gold mining. Maine's Bald Mountain is being developed by Boliden of Sweden.[1]
While some of this boom has come from enlargement or reopening of old mines, much is the result of a remarkable technological revolution, the new use on gold ores of an old mining technology called "heap-leaching," in which chemicals to remove the gold are sprayed on vast open-air piles of ore. But there is a side to heap-leaching which does not glitter: its environmental impacts.
GOLD AND CYANIDE:
Gold mining always requires plucking the gold itself from a much larger mass of rocky ore. When the gold occurs in fairly coarse grains in a gravel streambed, "panning" will separate it by simple gravity. More sophisticated methods are needed as ores are mined from rockier sources. Most of the deeper mines of the nineteenth-century American rushes employed mercury amalgamation to concentrate the gold powder after quartz ores were crushed in a stamp mill. The environmental residues from mercury amalgamation still haunt many streams, both in the Appalachians and the west.
Besides being environmentally hazardous, the mercury process was inefficient. Recovery of 60% of the gold in an ore was typical. Inventors searched for a better method, and in 1887 a workable process using cyanide was developed in Scotland; it went into immediate use in the newly-developed Witwatersrand goldfields in South Africa. The much greater efficiency of cyanide extraction, better than 97% in mills, made it profitable to mine much lower grade ores than could be done otherwise.
EXQUISITELY TOXIC:
But cyanide is better known as an extremely deadly poison than for its impact on the economic history of South African gold mining, and justly so. Sodium cyanide is "one of the most rapidly-acting lethal poisons and is well known to the public for such homicidal disasters as the Jonestown massacre and the cyanide-Tylenol deaths."[2] In lethal doses, which for humans can be as little as a teaspoon of 2% solution, the onset of symptons is reckoned by seconds. Death is very rapid.
Yet miners point out that there is no record of any person ever dying from a cyanide accident, that cyanide breaks down quickly in the environment, and that cyanide is a natural component of many biological processes. Why get so excited?
They have a point. The story is more complicated. First, the general term "cyanide" covers many compounds. All have in common the fundamental ion CN-, carbon combined with nitrogen, but beyond that the different combinations cyanide and the simple compound NaCN, sodium cyanide, the form used in mining as a solid or water solution.
Unlike many other environmentally-hazardous chemicals, cyanide is not known to bioaccumulate. It is not generally believed to be a mutagen or a carcinogen, though the research on this is inadequate.[3] Most ingested cyanide breaks down naturally; it is only fatal when a lethal dose is consumed at once - then it blocks the transport of oxygen across cell walls. In effect, the victim suffocates despite having fully-oxygenated blood; the central nervous system is the first organ to succumb.
In the natural environment, most cyanide breaks down harmlessly when exposed to sunlight or pH-neutral conditions. However, there is substantial evidence that cyanide persists in groundwater and in tailings or abandoned leach heaps, particularly where alkaline conditions are maintained.[4][5]
Given the chemical mechanism of its toxicity, it is not surprising that fish are particularly sensitive to cyanide in water solutions. Concentrations of HCN exceeding 0.1 milligram/liter can be fatal to sensitive fish species, and levels one-twentieth of that have been shown to prevent fish reproduction. The EPA's 1980 freshwater aquatic life criterion for free cyanide permits a maximum of 3.5 micrograms/liter for any 24-hour average, with a limit of 52 micrograms/liter at any time.[6]
Public attention, and the mining industry's response, have focussed on the spectre of deaths to humans from cyanide. Its long-term health effects have largely been assumed to be minor compared to the threat of immediate death, and ignored. However, there is good reason to suspect that a compound as aggressive as cyanide in lethal doses also has serious health effects in long-term chronic exposures at low levels. Correlations have been observed between chronic low-level cyanide uptake and specific diseases in humans, and experiments in animals have demonstrated progressive damage to nervous and other tissues.[7] [8]
And there is a great deal we simply do not yet know about cyanide and its effects. The high price of this ignorance has already been seen: "There is surprisingly little information on the interactions of cyanide with birds," a comprehensive survey reported in 1978.[9]
Tragically, a great deal of empirical evidence has been acquired since then. Many thousands of birds have died from drinking from open cyanide ponds at mining sites, because we later learned that birds are highly sensitive to cyanide.
HEAP-LEACHING:
For centuries, miners have sought ways to remove metal from an ore body without having to go to the expense of digging the ore from the ground, grinding it to a fine powder, and treating it in expensive facilities inside a mill.
At the limit, this ambition leads to in "in-situ" mining, in which a chemical solution is injected into the ore body from wells drilled into its place in the ground, and pumped out from extraction wells drilled in the ore some distance away. This depends on the ore body being naturally porous, or being fractured by blasting.
Gold mining by injecting cyanide into the ground has been tried in Colorado, but is not in commercial use. The U.S. Bureau of Mines suggests that it would be a good thing to try; they gloss over the threats of massive groundwater contamination which could result.[10]
From a miner's viewpoint, the next best thing to in-situ mining is to pile the ore up in large mounds and soak the mounds with a solution which will remove the metal. Moving a metal-bearing liquid is much cheaper than moving masses of ore around, and the metal can be extracted to produce high-quality product. This technique, known as "dump leaching" has been used in copper mining since its initiation at the Rio Tinto area of Spain around 1750.
In 1969, the U.S. Bureau of Mines proposed using open-air soaking with cyanide solution as a method of cheaply treating large volumes of low-grade gold ores.[11] The suggestion was timely. Rising manpower costs were making open-pit mines much more competitive with underground mines which required large amounts of hand labor, and new discoveries were made of low-grade gold ore in very large volumes. The low cost and ability to process immense amounts of material which characterised the new technique, which came to be known as "heap-leaching" attracted immediate attention, and as skill at the new technology has developed, its use has accelerated.
From its beginning at zero in the early '70s, heap leaching grew to an industry which treated almost four million tons of gold ore in 1980- one-third of all the ore processed in the country. By 1987 it had leapt to an annual rate of 65 million tons. Vat leaching (also using cyanide) had tripled in those seven years, but heap leaching increased sixteen-fold.
Still, for perspective, leaching of heaps and dumps of ore (a "heap" is ore piled over an impermeable liner; a "dump" is simply placed on the ground surface) in the copper industry consumes several times as much ore as in gold - over 220 tons in 1980[12] - and is growing rapidly, though not as explosively as in gold.[13]
The concentration levels of cyanide used in heap-leaching are quite low: from .015% to .25% of sodium cyanide by weight in solution.[14] It is common mining industry folklore that the solutions are not really dangerous. In fact, managers of heap-leach mines are fond of telling visitors that they could take a drink out of the solution ponds without any ill effects. However, a little calculation shows that, in fact, less than a quart of the lower-concentration leach solution holds a lethal dose.
PROBLEMS:
Because cyanide is so notoriously toxic, the mining industry is used to taking precautions. Any discussion of cyanide has to point out that there is no known instance of a human fatality from accidental cyanide poisoning in the mining business. This is a remarkable record, and a credit to the care and training of many users and the manufacturers, particularly DuPont.
However, to limit our concern over cyanide to human fatalities is to fall prey to what one biochemist calls "the dead body in the street theory of toxicology:" the attitude that if you don't see corpses, everything is okay. Despite the absence of human corpses, there is evidence that everything is not okay.
The most dramatic evidence has been the killing of birds from cyanide poisoning at mining sites. Thousands of waterfowl deaths from cyanide poisoning have been reported; more deaths are alleged to have been concealed, but we may never know. Even less knowable is the number of sickened birds which have succeeded in flying from the poison ponds, only to succumb farther along their flyways.
The mining industry has tried to reduce the toll, and responds angrily that waterfowl deaths have now been reduced to insignificance. However, discussions with wildlife officials indicate that cooperation is still limited and grudging. The State of Nevada has adopted a Memorandum which only requires that toxic solution ponds "be covered in a manner that will prevent or at least inhibit access by avian wildlife," and that the ponds "be made unattractive to wildlife."[15] The looseness of this State wildlife agency policy may result from the fact that it was actually developed by the Nevada Mining Association.[16] Federal land managers, with similar laxness, routinely fail to notify wildlife agencies of proposals for new mines so preventive measures can be planned.
There are more subtle threats from widespread cyanide use, in addition to dead birds and wildlife. Numerous leaks in the liners underneath the "heaps" have been reported. In several cases, the leaks have resulted in contamination of drinking water supplies. But there are probably many more leaks which are steadily projecting cyanide solution toward and into groundwater, undetected.
A layer of impermeable material is placed beneath each gold ore heap, to ensure that the gold-bearing cyanide solution winds up in the treatment equipment, and not in the ground. After all, recovery of the gold is what the entire operation is about. However, while there is an incentive to recover the solution, there is another to minimize the expense of the liner. Shortcuts in liner construction save money in the short run. "Many pad liners are punctured during heap construction," one trade article observes.[17] Early heap-leaching operations often used liners of clay, which are difficult to keep leakproof in practice.
Synthetic membranes are commonly used as liners today, usually of high-density polyethylene. But, because ore heaps for leaching are built up progresssively to as much as 150 feet in height, many liners will fail due to progressive settlement and tearing from the massive weight of material bearing on their thin membrane.
There has been little practical study of membrane performance under these conditions. In copper leaching, "dumps," piles which are simply loaded on the ground with no liner, are sometimes used. When liners have been proposed under copper ore dumps to protect groundwater, the industry response has been that "...it has not been demonstrated that [liners] are applicable to practices covering hundreds of hectares and containing millions of tons of ore. The massive size of such practices may result in shear forces that would destroy the integrity of a liner."[18] If liners are unreliable under copper ore dumps, why then should we have confidence about liners under comparable gold ore heaps?
There are yet cruder sources of cyanide discharge. At a small operation, a barrel of chemical may be tipped into a creek. A careless operatore may ignore a maladjusted valve in the complex piping circuitry of a large leaching site and not notice before tens of gallons of cyanide spill into the ground.
IF LEACH WE MUST:
To reliably prevent environmental damage, a mine and heap-leaching plant would have to address:
Rainfall management, to prevent the increased rainwater flow in the cyanide leaching system from causing overflow of leaching solution into streams and groundwater.
Surface water control to divert all streams and runoff around the mine area, and to prevent silt from being washed into streams.
Leak monitoring under the leaching pad and in the entire piping system. A double synthetic liner, over an engineered clay substrate, should be required, with leak monitoring between each of the three liners.
Provision of monitoring wells in the groundwater, with frequent testing. Several wells should be placed downgradient, with at least one 'baseline' well upgradient.
Wildlife protection, including positive physical prevention of any wildlife access to cyanide solution ponds or tailings where the concentration exceeds the Federal ambient water quality standard.
Reclamation and landscaping, with steps to prevent acid drainage and leaching of toxic metals from the abandoned piles of mine waste and the spent leaching heaps. This may require runoff controls, treatment of runoff streams from the waste, or capping of waste piles with impermeable clay layers.[19]
A long-term monitoring program should be required at all mine sites after completion of the mining and closure of the operation. This should include surface and groundwater testing, and a plan for corrective action if acid or toxic leakage develops.
Funding for these steps should be required to be guaranteed before the mining is permitted to start, so the public is not burdened with the costs of cleaning up after the mining companies after the glitter fades.
The impacts addressed here are only the immediate ones from heap-leach gold mining. The low cost and wide applicability of heap-leaching, the rush to new ores and the general permissiveness of the Mining Law and the Federal managers, lead to a dangerous synergy. But that is not directly the fault of leaching technology, or of cyanide.
VERDICT:
Can cyanide and heap-leaching be environmentally safe? Yes, technically, they can. Is some of the alarm over cyanide's use in mining unwarranted? Yes, technically, it is.
Do we have enough knowledge to take the risks we are currently taking with this aggressive poison? No, emphatically, we do not. Are the agencies on whom we rely to control the risks acting firmly and responsibly?
No, sadly, they are not.
The design requirements are inadequate, the agency inspection is nominal, the enforcement and penalties are less than lip-service. Because the spills have largely been remote, because the kills have been non-human species, we have not really awakened to this problem. We are spraying tens of thousands of tons of one of the most acute poisons known over the landscape.[20] There will be more deaths if this program is not strictly controlled, and they will not all be birds and animals.
The cyanide manufacturers, users, and regulators need to adopt an attitude of "yes, we have a problem; here is how we are treating it; come look." But too often, the reaction is "there is no problem, and go away." That will not reassure the public, and when the spills occur, the reaction will be bitter. It need not come to this, but I fear that it will.
"If you prick us, do we not bleed?
if you tickle us, do we not laugh?
if you poison us, do we not die?
if you wrong us, shall we not revenge?"
-William Shakespeare,
The Merchant of Venice,
Act III, Sc.1, Line 65.
Acknowledgements:
Sincere thanks are due to Frederick W. de Vries, of E. I. du Pont de Nemours & Company, Susan van Kirk, Dr. Glenn Miller, several anonymous agency officials (thanks, folks), and Congressman George Miller's staff for their assistance and data sources. The opinions in this article are the author's, and in expressing my gratitude to these folks I do not intend to imply any endorsement or agreement by them.
Footnotes:
Tons, throughout, refers to short tons, 2000 pounds.
[1] Mine production data and statistics generally are from U.S. Bureau of Mines publications. Boliden: Engineering and Mining Journal, July, 1989, p26.
[2] Medical Toxicology, Ellenhorn & Barceloux, Elsevier Science Publishing Co., New York City, N.Y., 1988;
[3] "Research Update," Rod Skogerboe, in Cyanide and the Environment, Colorado State University, 1985, p.552.
[4] "Long-Term Degradation of Cyanide in an Inactive Leach Heap," P.R. Engelhardt, in Cyanide and the Environment, Colorado State University, 1985.
[5] Goldfranks's Toxicologic Emergencies, 3rd Ed., Lewis R. Goldfrank et.al., 1986, p.587.
[6] "Physiological and Toxic Effects of Cyanides to Fishes: A Review and Recent Advances," Thomas A. Heming and Robert V. Thurston, in Cyanide and the Environment, Colorado State University, 1985, p.85.
[7] Reviews of the Environmental Effects of Pollutants: V.Cyanide, Oak Ridge National Laboratory, 1978, p.139-45.
[8] Goldfrank's Toxicologic Emergencies, 3rd Edition, Lewis R. Goldfrank, et al., 1986, p.592.
[9] Reviews of the Environmental Effects of Pollutants: V.Cyanide, Oak Ridge National Laboratory, 1978, p.8.
[10] "Gold and Silver Leaching Practices in the United States," U. S. Bureau of Mines IC 8949, 1984, p.4.
[11] "Recovering Gold From Stripping Waste and Ore by Percolation Cyanide Leaching," G. M. Potter, U.S. Bureau of Mines TPR 20, 1969.
[12] "Report to Congress, Wastes from the Extraction and Beneficiation of Metallic Ores,...," U. S. Environmental Protection Agency, 1985, p.2-22.
[13] Copper, Technology and Competitiveness, Office of Technology Assessment, OTA-E-367, 1988, p.73.
[14] "Gold and Silver Leaching Practices in the United States," U. S. Bureau of Mines IC 8949, 1984, p.8.
[15] "Cyanide Related Wildlife Mortalities," Memorandum, Nevada Department of Wildlife, dated 15 May 1988. Emphasis added.
[16] Nevada Department of Wildlife, letter to Lee Delaney, Surprise Resource Area Manager, 5 Oct 88.
[17] "Liner Design for Heap-Leach Pads," Mining Magazine, May, 1988.
[18] Copper Dump Leaching and Management Practices that Minimize the Potential for Environmental Releases, U.S. EPA Contract 68-02-3995.,
[19] A recent California State mining waste study (July, 1988) recommends that all mining wastes should be tested for their potential to generate acid runoff, as well as toxic metal content. Unfortunately, the science in these areas is not well-developed. Particularly, the long-term life of cyanide in groundwater is not completely understood.
[20] DuPont will not release production figures. The Nevada Mining Association states that annual cyanide consumption in that state is 80 million pounds, and Nevada delivers half of current U.S. gold production.
Bibliography:
- "Heap and Dump Leaching and Management Practices to Minimize Environmental Impacts," a useful article. Note the cost figures for reclamation steps given on p.372.
- "Gold and Silver Leaching Practices in the United States," U.S. Bureau of Mines Circular 8969, 1984.
- "Copper Dump Leaching and Management Practices that Minimize the Potential for Environmental Releases," PEI Associates report to EPA, 1986.
ENVIRONMENTAL IMPACTS
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