SRK Consulting, Moscow, Russia:

D. V. Ermakov, Senior Dressing Engineer

“Polymetall Engineering” JSC, Saint-Petersburg, Russia:

N. V. Vorobev-Desyatovskiy, Head of Department of Hydrometallurgy, e-mail: vdesjatovsky@polymetal.spb.ru

This article describes the processes of oxidation decontamination of cyanide solutions and pulps of gold-mining industry, which are most commonly applied in Russia and abroad. Unlike many foreign projects, Russian projects broadly use detoxification methods with application of active chlorine, which can successfully reduce concentration of free and WAD cyanides and thiocyanate content to existing Russian limits. In international practice, the most common methods are connected with oxidation of free and WAD cyanides, using Caro’s acid anions, generated in SO₂ – Cu²⁺ – O₂ and HSO₃^– – Cu²⁺ – O2 systems (INCO and Noranda processes, respectively). The considered foreign methods are significantly cheaper than active chlorine utilizing processes. However, they provide substantially poorer results in cyanide decomposition and show inefficiency in thiocyanate decontamination. An alternative way of decontamination of waste solutions and pulps, used in gold-mining industry, is application of Н₂О₂ with copper (II) compounds (Degussa process) and aldehyde (usually formaldehyde) in the presence of hydrogen peroxide (Dupont-Caston process) as cyanide oxidant. A method for decontamination of cyanide solutions and pulps, using Caro’s acid anion (HSO₅^–), generated from sulphuric acid and hydrogen peroxide, is genetically related with Degussa and INCO processes. The most recent and advanced development in cyanide solution decontamination is biological destruction of free and combined cyanide, described on the example of ASTER process. This article discusses the advantages and disadvantages of each cyanide destruction method, highlighting their compliance with existing Russian environmental conditions and regulations.

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