Located in Serbia, RTB Bor’s mining and smelting operation is the country’s only producer of copper and precious metals. With certified geological reserves for the mines at Bor standing at 5.1 million tons of copper, 1,477 tons of silver and 202 tons of gold, the mines have an estimated lifespan of over 50 years at current production rates. The two main open-pit copper mines, Veliki Krivelj and Cerovo, feed the local copper smelter and refinery that has been operating since 1961.

CHAPTER ONE

Ambitious growth targets

In 2010, riding the wave of rising copper prices, RTB Bor had ambitious goals to increase production from their current 8.1 million tons to over 10.6 mt through a series of upgrades and production improvements.  RTB Bor, along with many other companies in Serbia, looked to modernization as a way to dramatically increase throughput and efficiency to reach international standards.

With much of their existing equipment and machines at the concentrator plant over 30 years old and technologically outdated, it was challenging to achieve satisfactory production levels, and operating costs were also running high. Their flotation cells in particular were showing their age and were not up to date in terms of their levels of automation, adding a significant bottleneck to the production goals.

 

CHAPTER TWO

A 3% improvement in recovery with an advanced process control system

In 2011, a complete flotation plant, which included a total of 23 Metso RCS100 flotation cells and 16 RCS40 cells, was installed and commissioned at both the Veliki Krivelj and Cerovo ore processing sites. The work was carried out in seven phases to avoid production stops. These new flotation cells provided an immediate benefit with initial improvements of 10% in throughout and a 3% increase in recovery.  

The next step in getting the most out of the new flotation assets was to look at the overall automation levels for the flotation process. New plant automation, including several elements from Metso, was installed between 2013 and 2015. As an integral part of the flotation plant, Metso delivered a new Programmable Logic Controller (PLC) system that collects all of the key information from the flotation process. OCS-4D©, Metso’s advanced process control system, uses real-time operating data provided by a Metso VisioFroth™ system, other traditional sensors and online analyzers to achieve a further 3% recovery improvement.

“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 ore bodies. It takes just minutes to receive a chemical analysis, compared to the several days it took previously,” comments Saša Milić, Flotation Plant Manager. “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.

CHAPTER THREE

Taking a holistic approach to boost production results

To help RTB Bor get the most out of their new flotation assets, it was important to look at the process from a holistic point of view, with each component in the process chain carefully selected. Metso’s solution entailed a full-scope refurbishment process for RTB Bor’s flotation plant, including the new flotation cells, a Distributed Control Systems (DCS) automation design and tuning, as well as integrating an on-stream analyzer. The solution involved pulling from multiple Metso centers of expertise, including hardware engineering, automation as well as advanced flotation control, and was supported through local coordination. A major part of the solution was the installation of Metso VisioFroth with an OCS-4D to collect the right data and ensure that it was used to drive performance. 

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: “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, strong local footprint and expertise in process integration make it a reliable long-term partner and a global leader in this segment,” says Spaskovski.  

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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.

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CHAPTER FOUR

Metso’s HP 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.

A key milestone in the project was the replacement of the old Allis Chalmers crushers with modern Nordberg HP6 cone crushers. This makes a big difference for grinding.
Blagoje Spaskovski, General Manager of RTB Bor Group

20%

decrease in electricity costs

CHAPTER FIVE

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 MilićFlotation Plant Manager.

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.
Saša Milić, Flotation Plant Manager
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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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