Cyanide solutions are heavily used in open air mining process. It produces long and short term environmental damages. "It is estimated that 20.000 Ton / year are released to the atmosphere where this unacceptable process is used". The hydrogen cyanide gas will accumulate in the atmosphere and it will probably contribute to "unpredictable consequences for the atmosphere".

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As an introduction: Reflections

Technological advance should not be confused with progress. From an environmental sustainability or humanitarian safety point of view, there have been many incidents in the history of our industrial era that has demonstrated to us that some of the "advances" were really regressive. There are many sad examples which include thalidomide or the atomic bomb. The advancement of science does not always go hand in hand with the true progress of humanity. Let us observe with a critical vision that which is presented to us as "cutting-edge technology".

(...)

More than three months ago, we assumed the enormous responsibility of investigating the lixiviation process with cyanide solutions, reviewing publications and specific bibliography, to fulfill the extended role that we as teachers of a Public University have. We considered this task a critical one, so that all the citizens could have access to the minimum basic knowledge necessary to take a responsible position in front of this unexpected perspective. And so we did it, offering our information sessions / conferences to any person interested in acquiring information about this subject.

Dr. Silvia González, Lic. Marta Sahores

Environmental Impact due to the use of Cyanide in Open Air Mining

The lixiviation process with cyanide produces long and short term environmental damages.

Long term effects occur due to the cyanide residuals being injected in the dumps, the mobilization of heavy metals, or the generation of acid drainages.

Short term effects occur due to the accidents that can be produced during the operations, spills that can filter into the water tables or water channels in unexpected ways.

The chemical effects in the environment will be:

• The permanence of the cyanide and the effects of its decomposition products, which remain toxic for a considerable amount of time.
• The mobilization of heavy metals, and easy dissolution of its salts derivatives, due to the third effect (acid drainages)
• The generation of acid drainages (formation of sulfuric acid) produced by the oxidation of sulfide bearing rocks.

For a better comprehension of the subject, let's summarize...

Properties of Cyanide:

1. CAPACITY OF COMBINING WITH METALS: It is the key to understand its toxicity as well as its utility in mining. The cyanide combines with 28 metals of the Periodic Table, including gold, silver, heavy metals and iron. It is intended to be used in great quantities in the Esquel mine (180 ton./Month[1]).

Toxicity: Captures the Fe from the Cytochrome - C Oxidase, responsible for the breathing of the cells, therefore the cells die (they cease to breathe).

CN- + Fe èFe (CN)3

For this reason, cyanide is a poison for all living creatures. The lethal dose for a human adult is very small (150 to 300 mg.).

Utility in mining: It is used for its great combining ability with the gold, in a simplified form:

CN- + Au è (CN) Au

This process is called lixiviation with cyanide solutions.

Mobilization of heavy metals: The great ability of cyanide to combine with metals is not exclusive to gold and silver. It also combines with various heavy metals, such as mercury, arsenic, lead, and many others that are very noxious to living beings, producing another negative effect on life.

2. SOLUBILITY IN WATER: The salts coming from the (NaCN), as well as the compounds of lixiviated products (complex salts of heavy metals that are formed in the process) are very soluble in water. The water will then carry these toxins that are dissolved (the cyanide and the heavy metals) to wherever it can infiltrate.

3. CHEMICAL REACTIVITY WITH WATER:

If the water is acidic, it will form CNH(g) (highly toxic)
If the water is basic, it will remain as cyanide, which is the way that it is used in mining.

4. PERMANENCE OF THE CYANIDE FOR A LONG TIME.

The mining companies report that the cyanide is decomposed generating non toxic products.

Light
CN- + O2 NO3- + CO2

However, very difficult conditions are needed for this reaction to take place, in the case of contamination by filtering into the water tables or water channels.

This reaction needs plenty oxygen, a neutral medium and sun light.

In water tables, lakes and ponds there are many zones that are dark and without oxygen, where the chemical reaction could never take place.

Slow reaction: Even if the conditions are present, the reaction is very slow. And because it occurs in many stages, the presence of intermediate products are known to exist (also toxic), such as Cyanogens, Cyanates (which remain for a long time), Thiocyanates, Cyanogen chloride, Ammonium.

The U.S. Environmental Protection Agency (EPA) states that "the span of this reaction is unknown" [2]

The Environmental Impact Report foresees the addition of water with low pH to transform the cyanide into hydrogen cyanide, which is considered a "volatile element". Studies for the elimination of cyanide, made "in situ", assure that in 5 days the cyanide would become "volatile"[3]. However, the average life span (time that takes the concentration to reduce by half) of HCN is 267 days in the air, a much more prolonged time than what has been declared by the mining company and the Report.[4]

In the bibliography that was reviewed, "It is estimated that 20.000 Ton / year are released to the atmosphere where this unacceptable process is used"[5]. The hydrogen cyanide gas will accumulate in the atmosphere and it will probably contribute to the formation of other compounds which will have "unpredictable consequences for the atmosphere" like the ones known today as the greenhouse effect and the ozone depletion. Both result from years of emanation of carbon dioxide and Chlorofluorocarbons (CFCs) respectively.

Finally, the reaction is so slow that studies made by the Geochemist Robert Moran, demonstrated the presence of cyanide of several mg. per Kg. in Missouri (25 years after the mining operations) and in Auschwitz (45 years after the use of CNH gas in the chambers of death used by the Nazis)

There is no Cero Risk of Accidents

Some of the most important examples:

January 2000, the catastrophic cyanide spill of Baia Mare, in Romania that reached Hungary, Romania and Yugoslavia, affected the drinking water of 2.5 million people and the economic activities of more than one and a half million that lived on tourism, agriculture and fishing along river Tisza.

December 1992, the catastrophic cyanide and heavy metal spill of Summitville in Colorado, U.S., resulted after the company went bankrupt and left environmental damages that cost an estimated 150 million dollars to repair, and eradicated the aquatic life along 27 Km. of river Alamosa.

1992 - South Carolina (U.S.), more than 11.000 dead fish for 80 Km. as a result of Cyanide spill.

1994 - South Africa, 10 miners died when they were covered by a mixture of cyanide mud after a barrier from a tailings dam broke.

1995 - Guyana, more than 3.2 million liters of cyanide solution were poured into the River Essequibo. The OPS showed that aquatic life was dead for 4 km.

1998 - South Dakota (U.S.), 7 tons of cyanide solution were spilt, resulting in the death of fish and aquatic life.

Last moment changes

INCO Process

1. Cyanide decomposition: INCO Process "The process was changed in the last moment almost in the ending the present work" [6]: It consists of in treating the cyanide with sulfur oxide and oxygen. This treatment would be done in the plant before dump depositing, and it is assured (without certification from scientific publications) that the dam tails will leave the plant with a minimal percentage of cyanide (1 mg. per liter). On reviewing the Thesis "Microbe degradation of cyanide" by Eng. Marcelo Bellini, M.S. in Extractive Metallurgy, given to us by the mining company at our request, we found data indicating that < 3 mg. per liter is used for the INCO process and the confirmation (corroborated with other publications) that other secondary products that are yielded are also toxic.

In the conclusions, it is stated that "there is no chemical method that resolves from the technical and economical point of view, the cyanide residuals result of the mining industry". Lastly, with the known disasters in the past years in mind, it states that it is necessary to prevent reoccurrences by decontaminating the residuals, and Bellini's method of "Microbe degradation" was proposed.

2. Tailing disposition: (annex j Volume III, Pg. 13) proposes the option of the disposition of tails by means of injection in the dump of rock "based in the mining experience INCO's Mc Creedy and EAST Mine in Canada". And as a drawback of this procedure, it says that the method has not been experimented in mining, and VECTOR recommends that "the method must be tested in the fields ... to be able to evaluate its feasibility." To this respect, according to note in El Chubut newspaper in its 13th of November edition, Mr. Tufino, delegate of the mining company El Desquite, affirms: "as an answer for the requested by the Esquel community, about not to design a project with dam tailings with cyanide content, a unique technology has been developed, not yet used in the world which they intend to patent in a near future".

REVIEWED BIBLIOGRAPHY (among others)

• Journal of Toxicology & Environmental Health. Part A. 65(2): 149-163, 2002 Jan 25.
• Criteria Document: Hydrogen Cyanide and Cyanide Salts p.190 (1976) NIOSH (United States National Institute for Occupational Safety and Health);
• U.S. Geological Survey. Geoffrey S. Plumlee, MS973, Denver Federal Center, Denver, CO, 80225; (303) 236-1200
• United States Environmental Protection Agency (EPA)
• National Library of Medicine - SIS (Specialized Information Services)
• CCOHS (Canadian Centre for Occupational Health and Safety) 1996.
• Boening, R. A critical review: general toxicity and environmental fate of three
aqueous cyanide ions and associated ligands Water, Air, and Soil Pollution, 109 (1-4): 67-79, January 1999.
• Atkinson, R. Kinetics and mechanisms of the gas - phase reactions of the hydroxyl radical with organics compounds under atmospheric conditions. Chem. Rev. 85, 69 - 201, esp 159, 161, 1985.
• Korte, F; Spiteller, M. and Coulston, F. The Cyanide Leaching Gold Recovery Process Is a Non sustainable Technology with Unacceptable Impacts on Ecosystems and Humans: The Disaster in Rumania. Eco-toxicology & Environmental Safety 49(3):255-261, 2001.
• Korte et. al. (2000) Eco-toxicology and Environmental Safety 46, 241-245.
• EIA - VECTOR Company (2002)
• Gilman y Goodman (1994).Las bases farmacológicas de la terapéutica. Ed. Panamericana.
• Morán, R., (1998) Cyanide Uncertainties. MPC Issue Paper N°1.
• Morán, R. (2001) More Cyanide Uncertainties. MPC Issue Paper N°3.
• Bellini, M. (2001) Degradación microbiana de cianuros. Tesis de Maestría de la U.N. San Juan.
• Berlin-Declaration on Gold Mining Using Cyanide Process. Berlin (2000).
• Ley I-137 (1998) Estado de Montana.

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[1] Environmental Impact Report.
[2] Report from the U.S. Environmental Protection Agency (EPA)
[3] Idem 1 Volume III. Annex J
[4] Atkinson 1985
[5] Korte, F Spiteller, M. Pg. 244
[6] Idem 1 Volume II Pg. 7