Characteristics of the Second Washing of Metals

Physical Characteristics
Some old second washing of metals of amalgamation of color brownish reddish with predominance of the fine particles. The mineragraphic studies report a high level of oxidation with hematite, limonite, goethite, psilomelane accompanied by gangues of quartz.

Within the group of sulphurs-sulphosales, pyrite, galena and escase chalcopyrite and tetrahedrite within the crystals of pyrite have been able to be determined. We have not been able to observe no mineral typical of the silver, the existence of this element seems to be linked to the tetrahedrite and galena as a solid sollution and secondarily to the colloidal deposition of the cylomelane is observed non-metallic gangue which contains very small inclusions of pyrite and gold, the nuggets which constitute the sample, hsave been subject to chemical changes originated by the processes of meteorization due to the intemperism suffered.

Granulometric Characteristics
As one can deduct, silver is the main metallic value.

From te observations made we can deduce:

• - The mineral has been grinded and has a K80 of 650.
• - The 32.36% of the mineral is found in sizes lower than -325 net.
• - With a separation to -150 nets one would have a weight of 39.26% of the initial material with distribution to 63.16% in silver and 58.38% in gold and average laws of 26.59 Oz/TC of Ag and 0.58 Oz/TC of Au.

Experimental Programming
 Of all the traditional metallurgical methods known for the treatment of the silver and the gold the one of lixiviation with diluted of cyanide solution has been selected because of the fisico-chemical characteristics of the sampling of the second washing of metals being studied.

The basic principle of the process of cyanidation is the preferential dissolution of the gold and the silver contained in the sample, with a diluted solution of alkaline cyanide. The reaction commonly accepted for the dissolution of gold with cyanide is the following:

   4 Me + 8 Na CN + O2 + 2 H2O = 4 Me Na (CN)2 + 4 Na OH Me = Ag, Au

The following comparative systems have been considered in the study:

a) Direct cyanidation of the original second washing of metals.

b) Cyanidation of the fine fraction -325 nets of the second washing of metals (the thick fraction +325 will be concentrated by flotation).