Richard Fifer

RESPONSIBLE MINING IS TAKING PLACE IN SPAIN: BIOLEACHING FOR TREATMENT OF MINERALS

Lomero Poyatos will be more environmentally friendly

August 2011, Madrid

The CRI Company intends to use the bioleaching process for the treatment of ore. This process presents key environmental advantages. It is being developed with the collaboration of members of the School of mines in Madrid and involves the implementation of the most modern technology.

The pyrite Strip is characterized by mineral associations enormously complex as well as the sizes of liberation.

Gold in pyrite Strip is associated with iron sulfides, mainly with pyrite, also with pyrrhotite, and other sulfides: Chalcopyrite, galena, sphalerite and something with arsenopyrites. Pyrite is the most common that can be associated to gold and can be released by grinding more or less fine or if disseminated, as inclusions becomes refractory to conventional processes of leaching.

Refractory gold ores are characterized by low gold recoveries. The primary reason for this is a mineralogical response, with finely disseminated gold and intimately associated with mineral type pyrites and arsenopyrites. The traditional method of treatment for these types of minerals is through roasting oxidizing the sulfides, prior to the leaching with cyanide, but is expensive and undesirable environmentally.

Commercially viable alternative methods have been developed by eliminating the problem of the oxidizing roasting. These methods are: Bio-oxidation; Pressure oxidation; high pressure with cyaniding to low alkalinity. Oxidation to pressure, used in California, Homestakes Mc Laughlin and Gencor´s Sao Bento, Brazil, carries with it a complete oxidation of sulphides at 220 Kg/cm2 and temperatures of 180-210 º C., it is costly and aggressive. The use of high pressure has very specific commercial applications in the case of antimony products, stibnite and antimonite.

The largest recent development is bioleaching, especially attractive for refractory gold minerals, which is the case of gold in pyrites from the pyrite Strip, causing low recovery as a result of the presence of pyrites and arsenopyrites by traditional extraction processes typical in the case of strip minerals pyrite.

The Bio hydrometallurgy starts industrially in 1987 and already by 1989 several plants were launched, all of them by dynamic leaching and no battery to shorten times. Used reactors are classically used for dynamic leaching.

The process is caused by catalysis exercised by certain microorganisms during leaching during the leaching of some mineral ores. The micro-organism uses the mineral as a fuel, taking electrons for its survival. They do useful work by releasing heat and metals without requiring external power. Reactions occur at low pressures and low temperatures. Bioleaching is an attack and solubilization of ore through action of the micro-organism. This bacterial bioleaching on a commercial scale is currently being used in: refractory gold ores: pyrites and arsenopyrites.

ADVANTAGES OF THE PROCESS

a) Reduced energy requirements. Temperatures are reduced from 1500 ° C to less than 100

b) Reduced consumption of acids.

c) Low operating costs. By approximately 50%.

d) Enable the treatment of refractory gold ores impossible to treat by pyro metallurgy which are very difficult for other hydro-metallurgical processes due to high costs.

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