Floating to the top in minerals processing

Cobar, in the NSW Central West, is known for its historic mineralisation and high grades of copper and gold.

At Glencore International’s CSA underground copper mine, located just outside Cobar and run by Cobar Management Pty Ltd (CMPL) the miner was trying to make the most of these metal grades.

It devised a project which involved the replacement of the 30 existing scavenger flotation cells to increase processing at the site.

Originally, Outotec was brought in to replace the ageing scavenger cells in the miner’s flotation circuit with three new Outotec tank cells (TankCell 30s).

The ore processing superintendent at the site, Derek Beehan explained that "it was clear there was a lot to do before we could progress. Mid-December was our deadline and in April, when I started, we had our metallurgical production criteria, but had a lot to finalise, including the scope of works".

Although the flotation circuit at Cobar incorporated equipment from other suppliers, flotation technology from Outotec was chosen for the upgrade.

This initial scope developed into a far more comprehensive supply, with the miner soon requesting that Outotec supply engineering, design, install and commission the cells, and provide ancillary support (instrumentation, external launders and some piping) as well.

Site challenges

Concrete foundations were initially planned for the footprint, however, they proved too costly.

The most cost effective solution was to upgrade the existing steelwork for the cell installation.

This change from civil work to structural steel supports came late in the project, meaning that certain site elevations and dimensions were only confirmed six weeks prior to installation, so detailed planning and a teamwork approach was essential.

The upgrade was further complicated by a limited footprint and also the layout of the installation, as demanded by the process.

"It is always tight working indoors in a mill environment and here temperatures were up around 38-40 degrees," Beehan said.

"Dust, confined space and working in an operational environment made it difficult at times.

Further challenges arose due to factors such as limited crane access.

The flotation cells had to be designed in sections no heavier than two tonnes to facilitate an overhead travelling crane.

The restricted footprint also imposed a maximum height – thereby affecting not only the cells but also the support steelwork for the cells.

An appropriate design was also required from a maintenance perspective.

Result and benefits

Installation commenced mid-October 2010 and was completed by the end of December 2010, with commissioning in early 2011.

The installation was offline of normal production, apart from a tie-in to the existing plant when the cells were dry commissioned.

"The biggest benefit for CMPL is the reduced risk in cell structural failure causing unplanned downtime," Beehan explained.

"Also, due to a more stable control system, we can accommodate the fluctuations in our feed grades and throughputs that we experience in the plant.

"Another big benefit is energy savings. We are using three 45 kW motors with the new technology, versus 15 motors – drawing a total of 225kW previously. We’ve saved ourselves nearly 90 kW (40%), which is very important," he added.

On top of this, the site experienced significant savings on maintenance, with the 30 existing scavenger cell mechanisms replaced by only three Outotec mechanisms.

Spare part costs have also been significantly reduced and there has been no unscheduled maintenance required on the new TankCells.

Since the time of the installation, copper feed grade decreased from an average 4.9% in 2010 to an average 4.0% in 2011.

Both the overall copper recovery, at 96%, and the final concentrate copper grade remained constant, despite the lower feed grade.

This is a significant result, indicating an improvement in circuit stability and performance.

Copper recovery is expected to improve when the copper feed grade returns to 2010 levels.

The CSA Mine extracts over 1,100,000 tonnes of copper ore and produces in excess of 180,000 tonnes of copper concentrate per annum.

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