Published Jul 9, 2015

RTB Bor, Serbia: Copper ore production up, processing costs down

Together with Metso, the Serbian RTB Bor mine renewed the processing plant at its largest site, Veliki Krivelj. The result was a higher throughput and better recoveries with less energy consumption per ton of processed copper.

The renowned Serbian copper producer RTB Bor today enjoys the largest and most cost-efficient mining operation since the start of copper mining in the region of Bor, Serbia, 112 years ago. RTB Bor is located in eastern Serbia and excavates more than 40 million tons per annum of copper ore and overburden at multiple mining and processing sites: Veliki Krivelj (its largest site), Cerovo Mine, the underground mine Jama, the Smelter and Copper Slag Processing Plant, all of which are based in and around Bor, plus the Majdanpek mine and processing plant located some 80 km northeast of Bor.

Nine decades of partnership

RTB Bor and Metso share a very long history together: RTB Bor’s oldest equipment is a Metso-made cone crusher that was produced in 1927. The fact that the crusher is still running is evidence of the nine decades of partnership between the two companies.

Based on RTB Bor’s production growth strategy, its last five-year collaborative partnership with Metso resulted in an operational boost at its largest site, Veliki Krivelj: it revamped its crushing plant, refurbished the old grinding mills with the installation of newly designed rubber mill linings and a classification system, and built a completely new flotation plant with modern automation allowing for higher throughput and better recoveries with less energy consumption per ton of processed copper while never stopping its production.

In the constant race against time, costs and fluctuating copper prices, similar actions are being also planned and executed at RTB Bor’s other sites.

A major, positive impact to the RTB Bor mine economy

Metso’s assignment at RTB Bor was to come up with a holistic, integrated solution that takes into account the process from the mine all the way to the filtration. Maximizing the use of the existing infrastructure provided solutions with the lowest investment cost. All installation work was carried out with a minimum amount of production stops or disruptions to ensure constant cash flow for RTB. By mixing “tried and true” with “new and efficient” technology, higher plant availability was reached in a very short time.

The project was rolled out in multiple steps. The first step was the joint effort between RTB Bor’s maintenance team and Metso’s local service experts in 2009 to overhaul Metso’s Allis Chalmers 48 x 74-inch primary gyratory crushers. The secondary and tertiary crushing and screening plant was next on the list. The process started by assessing the condition of the existing crushing and screening plant and its design. Between 2010 and 2013, RTB and Metso focused on the efficient service and refurbishment of the existing equipment and the installation of three Nordberg HP6’s in the tertiary crushing stage to reach a finer, higher and stable production that enabled further optimization and increased capacity of the grinding sections.

The next step was to improve the grinding circuits. The three identical grinding circuits each consist of a combination of a primary rod mill and a secondary ball mill. After they were inspected, the grinding process with the finer feed coming from the crusher plant was simulated, and a new design for the grinding and classification section and the mill linings was developed.

A complete flotation plant that includes a total of 23 Metso RCS100 flotation cells and 16 RCS40 cells was installed and commissioned for both Veliki Krivelj and Cerovo ore processing. The work was carried out in seven phases to avoid production stops.

Blagoje Spaskovski, General Manager of RTB Bor Group, explains the boost in the old mine’s production results achieved through the close cooperation with Metso:

“Our mining operations at Bor and Majdanpek today have to mine lower copper grades of 0.3% before the open pits can be further deepened for the richer ore bodies. With Metso’s help, we were able to modify the minerals processing plant for better recovery even at variable and low copper grades, add an additional 6 million tons to our total annual production and achieve up to 14 million tons per annum production with the same building and energy infrastructure we previously used to float 8.4 million tons per annum.”

He continues: “In making the changes, the aim was also to raise the mine’s copper ore recovery percentage by more than 5% and decrease the electricity costs by 20% – all done with the lowest possible investment in buildings and by optimizing the use of existing infrastructure. With Metso’s minerals processing solutions, the mine has increased its production capacity significantly and, similarly, has decreased its crushing, screening, grinding and flotation costs by 15% per copper ton processed. This has created a major, positive impact to the RTB Bor mine economy.”

“With my long career of more than 40 years of experience in processing and flotation and in opening and operating nine different mine sites, I’m confident in saying that Metso’s minerals processing solutions, worldwide know-how, local strong footprint and expertise in process integration make it a reliable long-term partner and a global leader in this segment,” says Spaskovski.  

Metso’s HP6 crusher a proven step forward

 Spaskovski explains that the mine operation was successfully renewed in different phases:

“A key milestone in the project was the replacement of the old Allis Chalmers crushers with modern Nordberg HP6 cone crushers. In fact, today one HP6 does the job of two or three of the old crushers. The HPs allowed us to decrease the feed size to the grinding circuit from 25 mm to 100% minus 16 mm.”

“This makes a big difference for grinding. Electricity costs are a key issue for any mine, but this means that we can also grind much bigger quantities using the same mills and the same amount of electricity,” Spaskovski adds.

Double the lifetime with Metso’s mill linings

One of RTB Bor’s key renewal projects included installing newly designed rubber mill linings in Metso’s old Allis Chalmers grinding mills.

“Since installing the first Metso rubber linings in our ball mill in 2011, we have processed some 12 million tons of ore per grinding section; in early 2015, we changed the first mill head rubber linings but have not yet needed to change the shell linings. This means we doubled the lifetime with Metso’s rubber mill lining solutions that are now installed in all our ball mills at Veliki Krivelj and the Cerovo plant,” comments Saša Milić, Flotation Plant Manager.

Automation helps to react quickly

New plant automation, including several elements from Metso, was installed in 2013-2015. As an integral part of the flotation plant, Metso delivered a new PLC system that collects all of the key information from the process, as well as a new OCS Optimization Controlling System that works in tandem with the VisioFroth system and the cameras installed at all key flotation cells to enable full control of the plant parameters.

“With the new automation, we can see in real time what’s happening in flotation, and react quickly depending on the grade variations from four different orebodies. It takes just minutes to receive a chemical analysis, compared to previously when it took several days,”Milićcomments.

“As a result, we have succeeded in increasing our copper percentage in concentrate after flotation by more than 20%, which is a good achievement and sufficient for our new smelter,” he adds.

Vertimill enhances ore slag recovery

 The first phase of the slag processing plant reconstruction addressed the crushing and grinding circuits.

The slag coming from the copper smelter is crushed initially with the 1927 model Symons 5½-foot “oldie” and then with a new Metso HP200 cone crusher running in close circuit with a Metso CVB screen. The controlled – screened product from the crushing plant is fed to the grinding circuit. Fine grinding comes after primary grinding. Since May 2015, the fine grinding is performed with Metso’s Vertimill VTM 400 to a size of P80 of minus 40 microns at a rate of 42 metric tons per hour.

Metso’s Vertimill VTM400 vertical grinding mill significantly enhances RTB Bor’s recovery of copper slag reprocessing. After 1,000 hours of operation, the VTM400 has doubled the slag recovery rate, especially important since it has a 1.6–1.8% copper content.

Ivan Andelović, Main Engineer for the slag process, says: “The touch screen makes Metso’s Vertimill easy to use. Even after grinding the very abrasive slag that contains 50% silica, the magnetic liners and the grinding screw still look new.”

“The VTM400 is also easy to install and maintain, is quiet in operation and creates no vibration. Even a coin placed upright on the VTM won’t fall. Energy-wise, we save a lot of electricity because the vertical grinding mill can be operated with a small, 340-kW motor,” he adds.

“We are just waiting to get the automation system and individual flotation cells for the slag processing to get it perfect,” adds Goran Stojić, Flotation Plant Manager.

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