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HYDROMETALLURGICAL PROCESS FOR OXIDATIVE-AMMONIA LEACHING OF POLYMETALLIC ORES CONTAINING COPPER, ZINC, GOLD AND SILVER: AN ALT

Por: Álvaro Ordoñez Nuñez, Consultor Técnico y Edmundo Alfaro Delgado, docente de la Pontificia Universidad Católica del Perú. 


Abstract

Peru has several mining deposits containing gold, silver and base metals such as copper, zinc, lead and iron, both as sulfide and oxide mineralogical species. In southern Peru there are Zn-Pb-Cu-Ag-Au deposits with hybrid carbonate and polymetallic massive sulfide deposits in volcanic rocks.

The treatment of this type of minerals presents several difficulties for the recovery of all valuable metals. In this regard, preliminary technical research has been developed using the hydrogen peroxide/ammonia system. (H2O2/ NH3); peroxide acts as an oxidizing agent and ammonia as a complexing agent in an alkaline solution. 

We tested mixed mineral (oxides and sulfides) with commercial contents of copper, silver, gold and zinc; mineralogically constituted by chalcopyrite, bornite, brochantite, proustite, marmatite, pyrite, lead oxide in small quantities and carbonate gangue mainly. The particle size used was 100 M. Using H2O2/ NH3, with pH between 9.0 - 10.0, metallic dissolutions close to 90 % were achieved for copper, gold, silver and zinc. Lead and iron do not solubilize due to the alkalinity of the medium.

The redox potential achieved is sufficient for the dissolution of metal ions present in the sample and the ammonia holds them in solution because of its ability to form complex ions of Cu, Au, Ag, and Zn. Due to the high reactivity of the H2O2/ NH3 system, the prepared solutions remain reactive for 4 to 6 hours, which is sufficient time to achieve the required dilutions. 

For metal recovery from the leaching solution, zinc metallic cementation was used to precipitate gold, silver and copper. Zinc in solution can be recovered by electrodeposition.

It is worth mentioning that when cyanidation was applied to this mineral, very low gold and silver recoveries were obtained. Another advantage of using this method is the effect of self-agitation caused by the reaction of the leaching agent components, which causes effervescence in the solution. This allows the use of the Vat Leaching process.

The production cost competes favorably with traditional leaching systems, highlighting the great advantage that precious metals can be recovered together with base metals. Also because the required equipment and facilities are relatively simple and can be easily adapted to very small mining operations.

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