Helping a large copper/zinc mine meet the economic challenge of processing harder ore types

By Walter Valery and Edward Rybinski

Metso Process Technology and Innovation (PTI) has assisted Compañía Minera Antamina to increase mill throughput by integrating and optimizing blast fragmentation, crushing and grinding operations. So successful was this collaboration that Antamina has increased production targets by 50% and at the same time has minimized energy consumption per ton of product when processing hard copper and zinc ores.

                Compañía Minera Antamina is a polymetallic mining complex that produces copper and zinc concentrates as primary products and molybdenum and lead/bismuth/silver concentrates as by-products. Antamina, situated in the central Peruvian Andes around 4,300 m above sea level, represents one of the main complexes of the Peruvian mining industry.

                The advent of harder ores presented a problem for the operation, but Antamina technical and management staff worked with Metso PTI, and following the initial optimization of operating strategies in the mine and plant, mill throughput while treating hard ores increased from 2,750 metric tons per hour (mt/h) in 2007 to 4,000 mt/h in 2009. Continued application of the Process Integration and Optimization (PIO) philosophy and methodology delivered further improvement and ensured the concentrator consistently exceeded 4,400 mt/h while processing harder ores in 2010-2011. The significant increase in throughput and optimization of the overall production system also considerably improved the energy efficiency of the operation resulting in less energy consumption per ton of product.

The Challenge: Harder Ores
The Antamina mine, which commenced operation in 2001, had achieved the design capacity of 70,000 mt/d after five months of operation when treating copper ores (M1/M2). However, there were several issues associated with the treatment of harder copper/zinc ores (M4/M4A), which limited the throughput for these ore types to just half of the M1/M2 throughputs (i.e., 2,000-3,000 mt/h versus 3,500-4,500 mt/h).

                Achieving similar throughputs for both ore types became a challenge for Antamina. Metso PTI was engaged by Antamina to assist in increasing throughput of the difficult ores through the implementation of a PIO project.

Process Integration and Optimization Methodology
Metso’s PIO involves development of integrated operating and control strategies from the mine to the plant that maximize throughput, minimize the overall cost per ton, minimize energy consumption and maximize profitability. This methodology utilizes a combination of geological, geo-technical and quantitative information on ore petrophysical and comminution characteristics.

                Different ore types are characterized and tracked through the entire process (mine to plant). It is crucial that the ores being fed to the mill are characterized in the mine and then tracked through the downstream processes. Metso PTI has developed an ore tracking system named SmartTag that allows parcels of ore to be tracked from the mine, through the crusher and finally into the grinding mills. The SmartTag™ are built around robust passive radio frequency transponders. They do not have an internal power source, so they can remain in stockpiles and ROM pads for extended periods of time. Antennas to detect the SmartTags are located at critical points in the process ahead of the milling circuit; tags can be detected a number of times and provide valuable information on material movements. In particular, they make it possible to link the spatial data associated with the ore in the mine to the time-based or temporal data of the concentrator.

                Integrated, site-specific operating and control strategies are developed for different ore types with the aid of field measurements, historical data, audits and surveys, calibrated site-specific models, simulations and site validation.

                This PIO methodology offers a cost-effective and rapid route to increased profitability by increased overall production, reduced energy consumption, higher metal recovery and better overall process operation and stabilization. The measurement techniques have been developed over many years to suit the mining environment; they are inexpensive and can be easily carried out by mine personnel. The defined integrated operating strategies are implemented and monitored using established standards, quality assurance and control mechanisms to ensure benefits are maintained in the long term.

Implementing PIO
Metso PTI and Antamina personnel conducted a comprehensive review of existing operations at the mine and in the comminution circuits. Ore sources were characterized into domains of rock structure and strength with similar blastability and fragmentation properties. Blast design implementation, drill and blast QA/QC and the resulting fragmentation were measured in blasting audits along with vibration. These audits allowed benchmarking of existing practices in the mine and definition of main constraints related to wall stability, control, ore dilution and environmental aspects.

                Blasted material was tracked from the mine through the process using SmartTag ore tracking. Two antennas were installed at Antamina—one on the primary crusher product belt and another on the SAG mill feed belt—thus allowing performance in the crushing and milling circuit to be linked to the ore characteristics and blast fragmentation measured during the audited blasts.

                Metso PTI and Antamina staff also analyzed historical data, reviewed the current operating practices of the primary crusher, the SAG and ball mill grinding circuits, and conducted a number of audits and surveys. These data were used to develop mathematical models of the drill and blasting, crushing and milling operations. These resulting site-specific models were linked and simulations were conducted to identify optimum operating strategies for the overall process. The proposed strategies were discussed and analyzed in detail with site technical staff. The optimal and most cost-effective integrated operating strategy for the entire process (mine and plant) was then implemented in combination with other initiatives led by Antamina personnel.

Using Integrated Models and Simulations
The site-specific models for the blasting, crushing and grinding operations at Antamina were developed based on data collected on-site and samples taken from the mine and the plant before and during industrial trials. These models were linked to simulate the overall process. Inputs to these models include rock properties (strength and structure), blast design parameters (such as burden, spacing, stemming column and explosive type, quantity, etc.), primary crusher setting, SAG mill operating conditions and ball mill circuit conditions.

                The simulations at Antamina assisted site personnel to evaluate and establish optimum operating strategies and quantify the possible increases in throughput. Conditions such as different blast designs, primary crusher setting, SAG mill grate design, SAG mill ball charge level, ball mill operating conditions, changes in classification with hydrocyclones, use and operation of recycle/pebble crushers were all considered and evaluated in the simulations.

                The most cost-effective of these derived strategies were analyzed by a joint Antamina and Metso team and implemented on site. Following implementation of these strategies, SAG mill throughput when treating the harder copper/zinc ores increased from a target of 2,750 mt/h in 2007 to 4,000 mt/h in 2009 and 4,400 mt/h in 2010-11. Optimization of the overall process also resulted in less energy consumption per ton of product.

Continuous Improvement Delivers Further Benefits
After the initial success of the PIO project, Antamina and Metso PTI entered into a technical services support contract to refine and further improve the operation. Additional blast fragmentation improvement and its impact on blast damage and wall control was investigated as part of this contract.

                Following the PIO methodology described above, three trial blasts using higher energy intensity were conducted for the harder M4/M4A ore and campaigned through the plant to assess the comminution circuit performance.

                These higher energy intensity blasts produced even finer Run-of-Mine (ROM) fragmentation and subsequently finer feed to the SAG mill. The SAG feed F80 (size that 80% of the feed material is smaller than) was reduced to around 50–60 mm compared with 100–120 mm previously, and the percentage of fines (-10 mm material) was increased from 25% to 45%. Primary crusher power peaks were reduced significantly during these campaigns. To achieve best performance of downstream processes with the finer ROM, a number of changes and adjustments were made to the crusher, SAG and ball mill circuits. The resulting mill throughput averaged 4,100 mt/h for the three trial blasts and plant throughput above 4,500 mt/h was achieved for several hours during these trials.

                The optimization of the blast designs and subsequent downstream processes for each of the ore types ensured efficient utilization of the plant installed power. The additional blasting energy was more than compensated for by the large energy savings in the crushing and grinding processes, thus minimizing the specific energy consumption of the entire operation.

                During a base survey of the operation at the beginning of the PIO project, a throughput of 2,600 mt/h was achieved with specific energy consumption of 14 kWh/mt. At the end of the project, sustained throughput of 4,400 mt/h was achieved with specific energy of 10.7 kWh/mt. This represents a significant increase in resource efficiency by reducing the total environmental impact of metal concentrate production with an energy savings of 23% for Antamina.

                Continued implementation of the PIO philosophy at Antamina resulted in consistent and sustainable improvements in throughput and energy efficiency. Antamina continues to apply the philosophies of “integrated optimization.”

                The principal Antamina and Metso PTI team members were awarded the Coalition for Eco-Efficient Comminution (CEEC) Medal for their paper, presented at the SAG Conference 2011 in Vancouver, Canada, which described in detail this project’s background, methods and results.

This article is based on a paper originally presented at the SAG 2011 conference in Vancouver, Canada. Metso would like to thank Compañía Minera Antamina for permission to prepare and present the paper and produce this article. Contributors and authors of the 2012 CEEC Medal award-winning paper include Edward Rybinski, Jorge Ghersi, Frank Davila, Javier Linares (all Compañía Minera Antamina SA), Walter Valery, Alex Jankovic, Roberto Valle, Serkan Dikmen (all Metso Process Technology and Innovation). Edward Rybinski is manager of process studies at Compañía Minera Antamina SA. Walter Valery is senior vice president–global, Metso Process Technology and Innovation.