Degussa Aktiengesellschaft

Juergen Loroesch

Helmut Knorre

Annette Ziegler

Manfred Diehl

Joachim Fischer

Norbert Steiner

Ruediger Schuette

Herbert Riemenschneider

Andrew Griffiths

Josef Leutner

Christian Alt

Stefan Schulze

Karl-Heinz Koenig

Martina Claus

Heinz Moench

Steven Gos

Mathias Stoll

Eckhart Krone

Jochen Ullmann

New alkali metal cyanide granulates based on sodium cyanide or potassium cyanide and a method for their preparation are disclosed. Commercially available alkali metal cyanide granulates consist of irregular particles; disadvantages are in particular the tendencies to form dust and to cake. The disclosed alkali metal cyanide granulates demonstrate a reduced tendency to cake and virtually no abrasion. The granulates are characterized by essentially spherical particles with particle diameters in the range 0.1 to 20 mm, a bulk density of more than 600 g/dm.sup.3, an abrasion of less than 1%, and a caking index of at most 4. The granulates can be prepared by fluidized bed spray granulation involving spraying an aqueous solution containing alkali metal cyanide onto alkali metal cyanide nuclei in a fluidized bed and evaporating the water.

Process for preparation of alkali metal cyanide granulates

A process is disclosed for the leaching of gold and silver from ores and ore concentrates through intimate contact of the ore or ore concentrate with an aqueous leach solution containing cyanide. The leach solution has a pH of 8 to 13. The leaching process takes place in the presence of an oxygen-releasing peroxo compound. The separation of the formed cyano complexes of gold and silver takes place in a known manner. During leaching, at least one peroxoborate compound is present, in an effective quantity, as the peroxo compound. The peroxoborate is preferably a sodium or calcium peroxoborate. Compared to previously known leaching techniques in the presence of hydrogen peroxide or calcium peroxide, the leaching process according to the present invention provides a higher and/or faster precious metal yield and/or minimizes the consumption of cyanide and/or oxidizing agent.

Process for leaching of precious metals

A process is described for leaching gold and/or silver from ores or ore concentrates using an aqueous alkaline cyanide solution with addition of hydrogen peroxide. The addition of the aqueous H.sub.2 O.sub.2 solution is regulated and controlled through the concentration of the oxygen dissolved in the leaching solution, the leaching solution containing from 2 to 20 mg O.sub.2 and preferably from 7 to 13 mg O.sub.2 per liter. 0.5 to 5% by weight H.sub.2 O.sub.2 solutions are preferably added. The process is applicable both to leaching by agitation and to heap leaching, the addition of H.sub.2 O.sub.2 being regulated and controlled through measurement of the O.sub.2 concentration in the leaching solution and can also involve measurement in a measuring stream. Despite low consumptions of H.sub.2 O.sub.2 and NaCN, the gold yield is even increased in some cases and the leaching time shortened.

Process for the leaching of gold and silver with cyanidic leaching

A process for leaching gold and silver from ores and ore concentrates is disclosed using a cyanide leaching solution and hydrogen peroxide and maintaining an oxygen concentration of 2 to 20 Mg of O.sub.2 /liter. In the invention, leaching takes place in the presence of decomposition catalysts and preferably the formed cyano-complexes are separated during leaching from the leach solution. Decomposition catalysts are manganese compounds, present as 0.01 to 1 mg computed as Mn/liter of barren solution, or 1 to 50 mg computed as Mn per kg of ore slurry, or they are inorganic or organic polymers or carbon. Activated charcoal is preferred and simultaneously adsorbing cyano-complexes of precious metals. The process offers lowered consumption of H.sub.2 O.sub.2 and possibly cyanide and maximum gold yield in a shortened leaching time.

Process for leaching precious metals with hydrogen-peroxide and a

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Hanau-Steinheim, Germany

Juergen Loroesch