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Dec 12, 2016

Longer wear life and fewer liner changes reduce costs by 15% at Cobre Las Cruces

Grinding media has always been the second-highest operating expense, after energy consumption, for many mining customers. Reducing the consumption of grinding media while simultaneously improving grinding efficiency and reducing energy consumption are common issues in the mining industry. Read how Metso and Cobre Las Cruces worked together to find the best solution that resulted in savings.
Four employees at Cobre Las Cruces

Cobre Las Cruces (CLC), as the name says, is a copper mine located near Seville in southern Spain and is part of First Quantum Minerals Ltd. It is an open-pit operation and process plant that produces ‘high grade A’ copper cathodes, over 80% of them destined for the domestic market.

An atmospheric leaching process is used to recover the copper from the very rich Las Cruces chalcocite ore. Three crushing stages and a single grinding stage feed the mine ore to the leaching reactors and then further into the hydrometallurgical process. With an average copper grade of around 5-6%, the Cobre Las Cruces deposit is 7 to 12 times richer in copper than other similar mines. Processing 1.5 million tons of ore brings 72,000 tons of 99.999% pure copper every year. With an estimated mine life to 2022, Cobre Las Cruces is currently investigating further expansion possibilities.

View at Cobre Las Cruces mine

Exploration of the mine started in 1992 and production started in 2009. Since then, Metso has provided Cobre Las Cruces with forged balls (80 mm size) and linings for their 5 x 6.95 m primary ball mill.

 “Since the start, we’ve always been very satisfied with the quality of the products and service provided by Metso,” says Mr. Lucas Alcón, Minerals Process Manager at CLC. “During the plant studies, their EPC partner, SNC Lavalin, selected Metso for its high-quality products and proximity to the CLC-mine to be the supplier of the balls and mill linings. We’ve never had these products from other suppliers, as Metso keeps giving us the desired satisfaction one expects from their products,” he continues.

Working together to find the best solutions

Employee at Cobre Las Cruces

CLC has had several successful programs with Metso in order to reduce ball consumption and grinding ball inventory, save energy or improve the end product from the grinding stage. Since the start of operations, one real change was implemented and another might be just around the corner.  A couple of years ago, tests were done with feeding different ball sizes (80 mm and 60 mm) into the mill, but it didn’t lead to significant improvements. A decision was then made to continue producing with only the 80-mm size balls. A later test was carried out with harder grinding balls, and a significant increase in life-time was detected. The balls have a higher wear-resistance and keep their round shape a lot longer. Today CLC and Metso are planning a new pilot test with superior quality balls to determine whether the yearly ball consumption could be further reduced.

Mr. Alcón clearly states that all of these challenges are positively impacted by many factors, among which, for sure, is the quality of Metso’s grinding balls. “Since the start of the operations here, we haven’t seen any broken balls and the shape of the balls produced by Metso are close to being perfect,” he says. “These clearly influence the grinding efficiency and energy consumption in a positive way. Over the years, Metso has always partnered with us to find better solutions to these challenges. They bring us the best benefits when comparing grinding media and mill linings from other suppliers. Today our whole plant is running at over 95% availability, which is above international standards, and we’re sure that is partly the result of working together with Metso.”

After energy consumption, grinding media has always been the highest operating expense for many mining customers. Reducing grinding consumption while simultaneously improving grinding efficiency and reducing energy consumption are common issues in the mining industry. “Our grinding balls can help improve each of these in a significant way,” says Mr. Santiago Fernandez, Manager of Metso’s Forjas del Guadalquivir operations and manufacturing. “This, in combination with our proximity to Cobre Las Cruces, has benefited our valued customer. Thanks to lower inventory levels, lower ball consumption and more recovery, they are able to better use their financial resources.”

Longer wear life and fewer liner changes reduce costs by around 15%

In addition to the grinding media, CLC is also using Metso’s Poly-Met™ mill lining, which they are very satisfied with, according to Mr. Rafael Sánchez, Maintenance Supervisor at the CLC plant. “We are able to change the plates and lifter bars inside the whole mill in only 2 days; and since we are using the Poly-Met lining, we only need to do this every 7 to 8 months. This previously was needed every 4 to 5 months. This reduces our plant downtime and, consequently, also the costs involved. Since we changed to the Poly-Met mill lining, our costs decreased by around 15% due to the longer wear life and fewer liner changes. The Metso grinding balls also have a positive influence on the changing schedule, as the quality of the balls definitely increases the lifetime of the linings,” he stipulates. “Together with the Metso crew we’re now looking into increasing the lifetime of the mill linings even further by eventually switching to a thicker size. Many factors influence the time between changes (quality of the grinding media and mill lining, mill speed, mill lining design, etc) but we have no doubt that we’ll find the right balance with Metso’s help,” he concludes.

“Cobre Las Cruces is very happy with Metso’s support and collaboration. Having been able to reduce the consumption of grinding media by 10% has easily translated into savings of several hundreds of thousands of euros. Needing to handle fewer balls over time also has an effect on the health and safety of our people. Fewer ball changes needed and no broken ones inside the mill reduces the risk of accidents – and that is also worth mentioning!” Mr. José Luis Bonilla, responsible for external relations at Cobre Las Cruces, states. “The constant monitoring of operations and looking for improvements is an ongoing project. The material to be processed and the conditions often change, so there is no absolute solution for these topics. Close communication with our partners and a good understanding of our operations is therefore key – and Metso is definitely one of those partners!” Mr. José Luis Bonilla says.

“CLC cares a lot about the environment and is committed to it. We are working on continuously restoring the natural surroundings of the mine. All extracted material that cannot be sold is redistributed on the area around the mine. It is part of our management system and our company culture,” he concludes.

*After this article was written, Metso has divest its grinding media business to Moly-Cop

*Metso Outotec was formed July 1, 2020 when Metso and Outotec merged into one company. This case study has been written prior to the merger under the old company name.
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