Some Observations on the Chemistry, Toxicity and Analysis of Mining-Related Waters
The use of cyanide compounds in mining is frequently a controversial issue. Environmental groups often focus on the acutely toxic properties of many cyanide compounds to humans. The mining industry has argued that the dilute cyanide concentrations employed, the methods of use, and the rapid decomposition of these compounds make cyanide extraction a very safe alternative. Clearly the spill of almost two tons of sodium cyanide while being transported to the Kumtor mine, and the associated medical complaints and deaths have caused the public, especially in Kyrgyzstan, to reexamine these claims.
While it is reasonable to be concerned about the acute poisoning of humans and other organisms from mining related accidents, the more common environmental problems are likely to result from the chronic contamination of surface and ground waters by lower concentrations of cyanides and related breakdown compounds. Such chronic releases are much more difficult to notice and evaluate than are acute, high concentration spills that are often associated with rapid, observable deaths of aquatic organisms. Also, because mining-related waste waters are usually complex mixes of cyanides, metals, organic reagents and other anions, it is difficult to determine which chemical constituents are causing the toxicity problems.
Contrary to much of the literature published in mining and regulatory documents, not all of the cyanide used in mineral processing breaks down quickly into largely harmless substances. Many of the breakdown compounds, while generally less toxic than the original cyanide, are known to be toxic to aquatic organisms, and may persist in the environment for significant periods of time. Some of these toxic breakdown forms include the free cyanides, metal-cyanide complexes, organic-cyanide compounds, cyanogen chloride, cyanates, thiocyanates, chloramines, and ammonia. Unfortunately, many of these chemical species are not detected in the routine laboratory analyses normally performed on mining-related waters. Thus, it is often assumed that they do not exist. For many reasons, national and international regulatory (and lending) agencies do not require monitoring for many of these chemical species.