21st Century
Mining for
K-12 Educators

Mineral processing – Recovery of metals from the rock

Everything You Wanted to Know aout Cyanide


Cyanide is not the killer that is commonly perceived for two main reasons, 1) its concentration in most solutions for processing minerals is very low and 2) it’s an active chemical that wants to combine with iron or oxygen, etc. and then it becomes a very non-toxic chemical.  The only very toxic forms of cyanide are ‘free’ cyanide chemicals such as solid NaCN and gaseous HCN and CN- ions.  When these combine with iron in soils or with oxygen in air or water they become complexes such as CNO- or Fe(CN)6-4 that are thousands of times less toxic than the free forms of cyanide.  A 150-pound person could drink 3 large glasses of the strong cyanide solution at most gold leaching operations (125 ppm CN-) and not die because the dose is so low.  Hormesis is the concept that even though large doses may kill, small doses may be harmless or even beneficial.  It is not necessary to reduce the concentration of most chemicals to zero.  No one has died of accidental cyanide poisoning in the minerals business in the USA during the past 100 years.  Gold ore processing operations have multiple layers of protection to prevent cyanide from getting into the environment. 

Educators who wish to use portions of these free online lectures are welcome to do so as long as credit is given to CMAEF for its content.

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