There are many methods for extracting gold from cyanide leachate, such as carbon slurry (CIP), carbon immersion (CIC), magnetic carbon (MCIP) or resin exchange. Generally, the cyanide slurry is separated into a noble liquid (gold-containing solution) by solid-liquid separation, and the method for extracting gold from the noble liquid is a zinc displacement precipitation method, an activated carbon adsorption method, an ion exchange resin adsorption method or an electrolytic deposition method. It is a common method to replace the gold from the noble liquid with metal zinc wire or zinc powder. The precious liquid is clarified to remove the slime and suspended matter before entering the displacement sedimentation operation, because these impurities are used for the next replacement and sedimentation operation. harmful.
The basic principle of zinc replacement of precipitated gold is that the zinc in the noble solution will dissolve in the solution to precipitate the gold. The reaction formula of Au(CN)2 and Zn in the noble solution is usually written as:
There must be enough cyanide and alkali in the solution when the zinc is replaced. Otherwise, the dissolved oxygen in the gold-containing solution will dissolve the precipitated gold powder and oxidize the zinc to Zn(OH)2 precipitation:
Also, K2Zn(CN)4 in the solution will decompose into an insoluble zinc cyanide precipitate:
These zinc hydroxides and zinc cyanide are white precipitates that form a film on the surface of the metal zinc, which prevents the displacement of zinc from the precious liquid. Therefore, the addition of a small amount of lead acetate and lead nitrate to the sedimentation tank contributes to the dissolution of zinc and better replacement of precipitated gold. The inclusion of soluble sulfides, mercury , copper and other impurities in the noble liquid hinder the replacement precipitation of gold.
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