Por: Karim Batallanos, gerente senior de Procesos; Rafael Carpio, gerente técnico de Procesos; Antonio Bravo, superintendente de Metalurgia; Samuel Apolinario, supervisor Metalurgista; Hugo Toledo, supervisor Metalurgista y Sandro Frisancho, gerente de Producción de Procesos, Compañía Minera Antapaccay.

Abstract

Compañía Minera Antapaccay's concentrator plant has a SABC grinding circuit, composed of a 40' x 25' SAG mill, two 26' x 40.5' ball mills, two pebble crushers, a trommel-screen classification system in primary grinding and a hydrocyclone classification system in secondary grinding. This circuit, which was designed to process 70 ktpd of ore (76 ktpd of effective ore), has now reached a capacity of 95 ktpd of effective ore through the implementation of operational excellence initiatives, without significant investment costs. 

Although the increase in processing capacity has increased every year, the P80 of the final grinding product has also increased gradually without this meaning a loss for the process, since most of the ore in the deposit reaches an acceptable liberation grade between 240 and 250 microns (base of the geometallurgical model), however, the characteristics of the deposit and the occurrence of harder minerals generate variations in the size of the final grinding product associated with changes in the work index. 

In order to control the negative effect of an increased work index, improvement strategies and initiatives have been developed to control the P80 and reduce its variability, which include: 

ν Control of the F80 feed to the SAG mill. This variable depends on the result of the previous processes of primary crushing and blasting, and it is precisely in these stages where significant improvements have been made, creating a synergy between mine and plant that resulted in a sustainable reduction of the F80. 

Likewise, before feeding the SAG mill, there is a stockpile of coarse ore with four feeders, which have different grain size and ore competence due to natural segregation, which is why it was necessary to apply a comprehensive stockpile management strategy, which allowed balancing the stored load, the load sent to the Tintaya plant and the load that is fed to the SAG mill. For this purpose, the control system (DCS) established the continuous and controlled feeding of a minimum of 40% of the end feeders and the difference with the central feeders. Likewise, controls were established in the operation of equipment for transferring the stockpiled ore during crushing stoppages. This was crucial for the operation and, except for some exceptions, it was successful, which is reflected in the results obtained. 

ν Control of the feed of crushed pebbles according to the granulometry and competence of the ore fed from the stock pile. At this stage, conditional operating rules were established to work with one or two pebble crushers, which allowed sustaining the tonnage increase and progressively controlling the P80 variation.

ν Increased use of available power in the grinding circuit. For this purpose, changes were made: in the SAG mill, the slot configuration and design of the grids was modified; in the ball mills, the circulating load was reduced by changing the apex to vortex ratio, likewise, in order to increase the ball level and mill speed, the design of the ball retainers (spiders) was changed and hybrid liners were used in the mills; in the pebble crushers, the amount of fines fed was controlled by improving the washing system of the trommel and sieve; at the same time, the periodic closure of the CSS was standardized.

Each change made was supported by simulations and statistical analysis, which were fundamental tools for decision making.

The end result of the grinding improvements was a sustained increase in throughput, maximizing the use of installed power while controlling P80 variability.