Groundwater impact is a ruse for greenie shutdown. The real reasons are perhaps jealousy, and the motivation has scant to do with environmentalism.
Groundwater that takes that long to contaminate would not contaminate. It isn't like sewage or petroleum that never goes away, Cyanide "dies", becoming ferrocyanate, which are relatively safe, and carbon dioxide and ammonia. Once it has been in contact with limestone and iron minerals in the ecoystems it disappears. Simply put, cyanide is not a persistent, accumulating chemical in nature. Its biomagnification factor (BCF) is less than 100. For this reason it is ecologically and environmentally friendly although it is very poisonous at a fairly low level, and suddenly so. In other words at a very low level, cyanide becomes very non poisonous.
It takes at the lowest level 125 milligrams of cyanide to kill you by oral ingestion. The average may be higher than that. If the miner were using CIP or CIL technology, then the level of cyanide would be about 4-8 ounces per ton, or 125 PPM cyanide. To die you would have to drink 1 million milligrams or one litre of this water. When they kill the cyanide, the put thiosulfate in it before pumping it outdoors. There is no mine waste with cyanide in it in a heap leach mine. So only the waste water has any cyanide. They wash the waste down before disposing of it, so it is not a problem. If they kill let's say 95% of the cyanide before ponding the waste water, then the level is 6.25 ppm at that point. Still high, but sunlight will kill all that within 24 hours. But still it would take you ingestion of 20 litres of this waste water to die. 4.4 gallons. You would have to be fairly determined to try to kill yourself with mine pump out water. I still would not go near it at these levels of course. To kill cyanide really effectively I advocate a triple process of cyanide recovery, ozone and thiosulfate which should be 99.99% effective. Add in sunlight and you would get undetectable levels in one day. Cyanide is metabolized slowly, so has a time dependent toxicity. Small amounts do not accumulate like heavy metals.
What actually kills is the release of hydrocyanic gas into the stomach on contact of the cyanide with stomach acids. That is why the classic cyanide antidote for accidental oral ingestions is a carbonate? and ferrous substance mixed. It converts the cyanide to ferrocyanate so it cannot evolve gas. First line antidotes are Amyl nitrite (inhalers), 3% sodium nitrite and/or 25% sodium thiosulfate solutions (by injection). Also used second line are hydroxycobalomin (first or second line), vitamin B12 or cyanocobalamin by injection and rhodonase. (by injection). Cyanide may be absorbed by the skin and mucous membranes lips and eyes. It is extremely dangerous to handle cyanide compounds dry or wet, or solutions with unprotected skin. At low Ph cyanide releases gas slowly when it is wetted. There are new oral antidotes since 2008 which are reputed to be fast (3 minutes) and effective. I don't know their chemical formulae. Also there are new substances which will increase one's resistance to cyanide, which after the fact may be a life saver especially in smoke inhalation cases. The new oral antidote has something to do with 3-mercaptopyruvate and sulphane. Sounds Like NAC, B6 and sulphurophane, BWTFDIK? NAC is a prodrug of cysteine, with sulphur. This antidote is a prodrug of 3-mercaptopyruvate.
ncbi.nlm.nih.gov
The classical antidote treatment is what is called extreme, possibly dangerous. They even advocate titering the blood for cyanide before adminstering the thiosulfate. (50 mls solution.) The solutions you mix and drink are not of proven effectiveness, (how could they tell?), and they are considered toxic in and of themselves, though nowhere nearly as toxic as cyanide. Poisoning in gold recovery plants is extremely rare. Workers at the Cobalt silver refinery got cyanide rash on regular occasions indicating exposure, but never were made ill by the substance. At Kerr Addison we did cut and fill with paste that was waste from cyanide treatment, and it had a particular smell which we were told was cyanide. Perhaps as much lime from cement as anything. At any rate it never poisoned anyone.
If there is no liner of clay or plastic on the pond, then there may develop very small (100 metre) groundwater plume of perhaps 100 ppb CN if the mine is not paying attention to cyanide killing with thiosulfates and ore chlorine. The level acceptable in drinking water is 20 ppb.
The body has sulphanes that kill cyanide, which is why you can smoke cigarettes and not die, as smoke is the prime natural contained or CN in the biosphere. (That is what people die of from smoke inhalation is cyanide poisoning.) Since man has lived around smoky fires for millenia he probably evolved cyanide killing genetics. Fish, Dogs and other animals are much more sensitive to cyanide.
Metal plating plants and jewelers in Mexico and the rest of North America use 12 times more cyanide than all mining does. and they flush the waste liquor right down the storm sewers after killing it with sodium thiosulfate. It goes right into our drinking water! I don't see anyone complaining. Cyanide has not been identified as a long term carcinogen or have other health effects that are insidious at very low level exposure. Cyanide compounds at very low levels are naturally occurring in grasses, fruit seeds, vegetables and flowers.
The bottom line is with modern plant methods, the residents of San Luis Potosi at 8 miles from CSP and the mine site, might as well be on another planet as far as danger from cyanide. I would if I were resident of Cerro San Pedro be more concerned with dust from the pit than plant chemicals. They cannot do much about that, and it is a bit of a problem. At the end of the day the mine will create a huge hole in the ground. It won't be the best looking natural feature on the planet, but while it is being made the residents can at least make a good living. For the 45 residents of Cerro SP, it might be an acceptable trade off.
What people around the world have to come to terms with is that our civilization depends on metals and other earth resources. Without steel, zinc, copper, gold, titanium, tin, lead, aluminum, calcium (cement), nickel, cobalt, chrome, aggregate, silver, silicon, glass, tungsten, petroleum, natural gas, sulphur, germanium, PGMs, we would live in a much different world. Take any of those metals out of your world today and try to do without them. Gone would be automotive transportation, cooking utensils, electric power and everything that flows from it, refrigeration, television, computation, telephone, etc.. pots and pans. Medicine. Food storage. Bearings. zippers. Defense. The clothes on your back. What good is a domestic supply? Cost, and strategic value. CAn we make do with scrap? Apparently not, and then the environmental maniacs would get on our case about scrap piles. They already do that. We need a metal industry to feed industry which feeds construction and machinery for building and repair.
Canada was an example of a country that was self sufficient in many ways. We grew our own food, although we liked to get fresh veggies from California, imports were not absolutely necessary. Our vehicles and machinery were made from our own resources, mined here. Jobs were available at all levels from mining to manufacturing to engineering to sales. Our mining markets overseas and domestically developed from our homegrown trained cadre of miners and engineers and financial people. What put the screws to all this was a combination of US and domestic political manoeuvers. All the provincial and federal politicians at once got the idea that being in the basic trades was somehow bad. We are only hewers of wood and drawers of water they averred. It was a common political phrase. From being merely fur fish and wheat traders we had become lowly rock breakers. We wasn't really skilled. That is what a lawyer might think looking at a mine, but obviously they never engineered one. Like the military, every science known to man is used in building a mine. Mechanical, chemical, ferrous metallurgical, hydrometallurgical, electrical, process and geological engineering is used, and at the highest level. Geophysics would not operate at all without computers. Even buildings today are put together with finite element analysis. Rigorous examination of economics of mines takes advanced math and other science. You have to put the thinking cap on as assuredly as if you were a specialist in biochemistry or computer science. What the politicians seemed to want from the late sixties on was a building of technology without the trade and materials to support it. Technology development needs markets and these markets must allow entry. Difficult when Japan was one-way trade. Junk for our cash. We lost our march in the world when we turned our back one what the politicos called "sunset smokestack" industry. Despite the dream of politicos to build a service nation that supposedly learns its skills out of the thin air or pure knowledge with no practice, we have ended up with one depleted of the renewables such as fish, and wood, and dependent on another non renewable, oil desperately for its very sustenance. Without oil and with "free trade" Canada would be headed to becoming a third world nation a few years. But you never hear them complain about that. Ottawa energy policy is all about keeping their friends employed.
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