Gold Cyanide Method

 Gold cyanide method is the process of dissolution of gold ore using cyanide chemicals, because every atom of gold requires dissolution of the mineral carrier or impurity with the stoichiometry of two cyanide-soluble compounds.

Gold cyanide process begins with Carl Wilhelm Scheele had discovered that the gold will be dissolved by cyanide in aqueous solution. And this gold cyanide process he discovered in 1783.

Gold cyanide method is a basic method of the gold dissolution process is often used in gold mining around the world, and gold cyanide process has been patented in 1887. The chemical reaction that occurs when the dissolution of gold cyanide is:

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

In the process of redox, oxygen removes electrons from the gold four simultaneous with the transfer of protons (H +) from water.
Mines that have used the cyanide process of gold mineral dissolution is:

  • Crown Mine, New Zealand in 1889 
  • Robinson Deep, South Africa in 1890
  • Mercur, the United States in 1891
  • El Oro, Mexico in 1900 
  • He Belliere, France in 1904 
      The function of the gold cyanide method is to increase the recovery of gold and silver below 70% to better than 90% because of the gold minerals are encased by silica rocks are smooth and have a low grade that can be directly by the solvent extraction of cyanide. In some ores, particularly those who are most sulfidized, aeration (before the introduction of cyanide) from the ore in water at high pH can make elements such as iron and sulfur are less reactive to cyanide, and therefore the gold cyanidation process more efficient. 

In particular, oxidation of iron to iron (III) oxide and subsequent precipitation as iron hydroxide to minimize the loss of cyanide from the formation of iron cyanide complexes. Oxidation of sulfur compounds to sulfate ions to avoid the consumption of cyanide byproduct thiocyanate (SCN-). Typical cyanide concentrations used in practice range from 300 to 500 mg/l (0.03 to 0.05% as NaCN) depending on the mineralogy of the ore. The gold is recovered by means of either heap leaching or agitated pulp leaching

   Cyanide is a universal solvent the processing of gold at gold cyanide method, and a weak solution containing a quantity of sodium cyanide (0.015 percent average) is percolated over crushed ore to dissolve the gold. 

The leach solutions are carefully buffered with an alkali (usually lime) to prevent the possible generation of hazardous hydrogen cyanide gas. The gold bearing solution is collected and the gold removed. The leaching solution is then reused. 

The whole process takes place on top of an impermeable, double or triple layered liner to collect all of the valuable gold and prevent the escape of dangerous CN. And solvents commonly used in the processing of gold by cyanidation is NaCN, KCN, Ca (CN) 2 or a mixture of these three parts sianide. 

However, for solvents that are often used in the treatment process is being able to dissolve gold NaCN better than the other solvents. Cyanide NaCN, KCN, AgCN that is in use in the processing of gold and usually shaped salt crystals are also often used for photographic, metal plating and staining. In the metal plating, acid cyanide used in the cleaning process, hardening and metal plating metal to obtain seeds from the seed of pure gold metal.

 Some characteristics of the type and function of cyanide in an industry : 
  • KCN: This salt (in trading) contains 90% chloride, carbonate, cyanida of potassium. Used for the chemical reaction process, the company electricity company, and photography. But now widely used calcium salt and sodium salts are cheaper. 
  • Ca-Cyanide: Used in mine industry mining. 
  • Na-cyanide: Used by companies metallurgy, electricity, metal bjiji seed hardening, tanning and paint companies 
  • Silver-cyanide: Used by companies of silver because it is insoluble in water, quickly broken down by stomach acid and acid generating hydrocyanida
Cyanide derivatives 
  • Acrylonitrile (CH2 = CHCN): The manufacture of rubber used in the process of synthesis. 
  • Cyanamida (HN = C = HN): used for artificial fertilizers and as a source hydogen cyanida.    
  • Nitro Prusida (Fe (CN) 5 (ON): used for the manufacture of chemical synthesis. 


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