Cyanide is poison. Detective writers like it. Gold miners like it. The environment; not so much. In the year 2000 cyanide got into the Tisa river and then into the Danube through a small Austrian gold-mining company's efforts using cyanide to extract gold and silver from solutions. Fish, birds and wild animals died and millions of inhabitants in Hungary were deprived of drinking water.
To prevent future occurrences of that kind, Russian researchers from the Krasnoyarsk State University and the Institute of Chemistry and Applied Chemistry have developed an original method for extracting gold and silver from multicomponent solutions.
They managed to find an adequate and less toxic replacement to cyanide – the reagent which is widely applied for extracting gold from ore and recyclable materials and which is even called a “poisonous companion of gold”.
Basically, the method developed by the Krasnoyarsk chemists does not differ fundamentally from the known one. In both cases, the reagent is added to complicated solutions containing a noble metal– for example, after ore dissolution, or as the specialists put it, opening up of ore. The reagent forms a complex both with gold and silver. Thus a compound is obtained, in which the central atom of the metal is surrounded by several ions – either those of cyanide (as usual), or of thiocyanate (a new method).
The entire construction is an anion, and it can be further extracted from the solution on the so-called ion-exchanging column – chlorine ions can be “changed” (they go into the solution) for composite ions that contain the noble metal in the ion-exchange resin filling the column.
Then these ions, certainly together with silver and gold should be washed off the column, and the target metal should be educed from this solution – it can be reduced electrolytically or by any other method.
However, this seems simple only on paper. But in real life chemists had to perform tremendous work to select the most efficient sorbent and conditions of dealing with it to “catch” maximum noble metal from the solution and then to wash all of it off the column, it is desirable to do that separately. And they have succeeded in doing that.
The researchers not only investigated the sorbtion mechanism of thiocyanate complexes of gold and copper on very different sorbents, but they also discovered those that enable to extract practically all noble metal from the solution. Moreover, having designed the necessary methodology, the authors learned to fully separate gold and silver, varying the solution composition, which “washes off” the target metal from the sorbent.
Besides, the researchers developed and patented the method that allows to determine the gold content directly in the sorbent, but not in a ready solution. Of course, this is very convenient – because this allows to learn exactly how fully the noble metal was extracted from the initial solution and then – how fully it was extracted from the sobent.
In brief, the researchers have developed an excellent method for extracting gold and silver – it is efficient and much less poisonous the traditional method. Cyanide is almost one hundred times more toxic than thiocyanate. So, the Krasnoyarsk chemists have managed to relieve gold at least one poisonous companion – cyanide.