Por: Pitter Huapaya Chumpitaz, gerente de Procesos; César Espejo Rodríguez, superintendente de Planta, y Pedro Gonzales Andia, jefe de Lixiviación, Pan American Silver.

Abstract

At our La Arena process plant, one of the main chemical inputs in our process is sodium cyanide. Gold leaching with a cyanide solution remains the most widely used hydrometallurgical process for the extraction of gold from ores. Sodium cyanide, being an essential part of the process, also has a high impact on the operating costs of the area.

Based on metallurgical test results, it was concluded that, starting in the second half of the ore leaching cycle, the cyanide requirement to continue gold leaching is lower. For this reason, the feasibility of implementing a pumping system to perform a differentiated irrigation in the pad and thus optimize the consumption of this reagent was analyzed.

The system allowed the addition of concentrated cyanide solution (make up) to cells with fresh ore and the use of lower cyanide concentrations for cells with ore that were in depletion or second leaching. Thus, the operation began to reduce the concentration of cyanide in the irrigation solutions for depleted cells with 40 ppm of free cyanide and to optimize the irrigation of cells with fresh ore with cyanide concentrations between 80 and 100 ppm, depending on the operation's criteria.

The project reduced the sodium cyanide consumption ratio in the leaching pad from 0.22 kg/tm to 0.18 kg/tm; in addition, the following benefits were obtained:

ν Better administration of sodium cyanide in the irrigation solution.

ν Opportunity to irrigate fresh cells with high cyanide concentrations and improve leaching kinetics.

ν Decrease the leaching of metals such as copper and mercury, which generate problems later in the process.