cyanidaatio

Cyanidation, also known as the cyanide process, is a hydrometallurgical technique used primarily for extracting precious metals, gold and silver, from ore. It relies on the ability of cyanide ions to form stable, water-soluble complexes with these metals. The most common reagent used is sodium cyanide (NaCN) or potassium cyanide (KCN).

The process typically involves crushing and grinding the ore to increase the surface area. This finely ground ore is then mixed with a dilute solution of sodium cyanide, often in the presence of oxygen, which is crucial for the oxidation of the metal. The chemical reaction for gold is often represented as:

4 Au + 8 NaCN + O2 + 2 H2O → 4 Na[Au(CN)2] + 4 NaOH

The gold-cyanide complex (sodium aurocyanide) dissolves into the aqueous solution, separating it from the solid waste material (tailings). This gold-laden solution, known as pregnant leach solution (PLS), is then separated from the tailings, usually through filtration or thickening.

The dissolved gold is subsequently recovered from the PLS. Two common methods are the Merrill-Crowe process, which involves deaeration of the solution and then adding zinc dust to precipitate the gold, and adsorption onto activated carbon, followed by elution and electrodeposition. Environmental concerns regarding the toxicity of cyanide necessitate careful management of the process and waste streams, often involving detoxification steps before discharge or disposal.