March/April 2015

Science in the art of flotation

Froth cameras allow operators to precisely monitor and analyze flotation

By Alex Lopez-Pacheco

While the science behind froth flotation – one of the most critical processes for mineral recovery – is essential, the optimization of a flotation circuit has traditionally had the elements of an art form. Artists, however, are in short supply. This has plant operators increasingly calling on the maturing technology of froth cameras to improve efficiency and output.

Achieving the basic frothing concept of separating hyd­ro­phobic material from hydrophilic material – where the former repels water and the latter attaches itself to water – is no easy feat. “You want the good minerals, the hydrophobic material, to go up to the top in larger bubbles and the bad minerals to fall to the bottom,” says Tom Fulton, operations manager for Imerys Talc’s Penhorwood mine in Timmins, which installed froth cameras last November. “We can always make the bubbles rise harder and faster by adding more chemicals or more air but the cost of that is the purity goes down a little bit. The larger the bubbles you have, the faster they rise, but that doesn’t allow the impurities as much time to go down.”

Finding the perfect balance has historically been the role of flotation operators, who monitor the froth visually. They used their in-depth expertise, attained by working for years inside a plant, to understand the froth’s characteristics and changes. “An operator could look at the froth and tell you exactly what it was doing, but those skills have largely been lost,” says Michael Schaffer, president of Portage Technologies, a Toronto-based company that focuses on intelligent technology for mineral processing.

As with any connoisseur, an operator needs a combination of hands-on experience and talent to be able to assess froth visually. But relying on individuals creates room for human error, regardless of their level of expertise. “Back in those days, it would change from day to day,” says Schaffer. “The operator could see the same froth differently from one shift to the next, resulting in inconsistent control. A metallurgist would look at the froth in the cell and say the cell had to be pulled a bit harder or slowed down. However, exactly what that meant was all subjective, as each operator would have their own interpretation.”

Additionally, an operator simply does not have enough time in one shift to continuously monitor each cell. “A floatbank is typically quite large, particularly when you get to columns and you have to climb up the stairs,” says Schaffer. “How often does that operator walk and see an entire circuit over the shift?”

Today, there is another option for mining companies: froth cameras strategically placed above each cell that monitors the froth. “The camera captures the images and sends them to a computer for analysis,” says Hugo Araujo, ‎a solutions specialist with SGS Advanced Systems, which offers intelligent systems that include froth cameras.

The software that conducts the image analysis is where the real science in the technology lies. A single camera cannot record the entire froth surface due to its surface area, explained Araujo, so the software selects one or more areas of interest to represent the conditions of the entire cell. The algorithm is capable of counting, identifying the bubbles by size and tracking the speed of their movement. Based on this, the overall speed and quality of the froth can be calculated – and the air and reagents are adjusted automatically or manually.

“The mantra in the industry is that you can only manage what you measure and you can only optimize what you can control,” says Schaffer. “With froth cameras, now when someone says, ‘Let’s pull it a bit harder,’ he can be specific and say, ‘Can you increase the cell velocity by 10 per cent,’ and you can actually dial that in because you are directly measuring your mass pull and quality of the froth.”

The cameras, which look like security cameras, also allow for real-time monitoring of all the cells across the circuit. If the cameras are connected to a plant’s flotation control system, the software analyzing the images can automatically make adjustments. As well, an operator can view and monitor all the cells from a display in the control room at all times. “The computer is much more rigorous than a human,” says Fulton. “It’s quite happy to look at the bubbles every second, year after year, and not get tired. It’s more statistically rigorous. It’s actually calculating a number. Operators are not using math. They’re using their opinion.”

Rapidly improving technology

While froth cameras have been around for close to two decades, the technology has leaped forward in recent years.

One of the problems with the older software, for example, is related to using only one area of interest, typically near the lip of the cell. The velocity of the froth varies within the cell, slower in the centre, and faster near the lip. Different factors, including buildup in some areas can also result in speed variations. While it is still possible to mathematically calculate the overall froth speed, this was not always properly done with older systems.

This was one of the issues that led Copper Mountain Mine near Princeton, B.C., to hire Portage to upgrade its controls system, including its existing froth camera system.

“Basically, you end up with froth that’s turning around on the surface and has an apparent velocity in the area of interest, but it’s not actually being pulled because the froth level is lower than at the lip,” says Mike Westendorf, the mine’s ‎mill superintendent. “Portage added algorithms to correct that.”

In fact, says Schaffer, a single Portage camera can simultaneously look at three areas of interest and use the data to calculate the lowest, average and fastest velocities within one cell.

Portage’s controls and froth cameras system also helped Barrick Gold Corporation’s Porgera mine in Papua New Guinea overcome its difficulties with overflowing launders – a problem older cameras would not have been able to detect. “When you’re looking at the top of the cell, the top layer of the froth looks as if it’s not moving, but what’s actually happening is the launder is overflowing and the slurry is pouring out onto the floor,” says Schaffer. Old cameras would have seen the top layer and indicated a need to speed up the froth, when in reality the correction needed was the opposite. Porgera installed a shiny plate on the launder, making it one of the camera’s areas of interest. Now, when the plate starts to get dirty, the system recognizes the launder is overflowing and automatically slows down the cell.

Maintenance also used to be a source of grief. To capture the best image, the camera lenses had to be clean and the area well lit, which meant regular cleaning and light replacements. Plants are now equipped with long-lasting LED lights, more robust cameras and diagnostics that inform operators when the camera lens needs cleaning. In addition, modern cameras use five megapixel lenses. “We can put them farther away from the cell, which means they stay cleaner,” says Schaffer.

One of the most dramatic changes in the technology has been cost. Twenty years ago, a froth camera system was a hefty investment as one camera alone could cost between $25,000 and $35,000. Now installation plus any additional engineering can run up to about $8,000 per camera. Even with a control system for automatic frothing adjustments, the typical total cost can range between a few hundred thousand dollars and some $500,000. Most new mines now include froth cameras as standard equipment and the number of established mines installing them keeps growing, says Schaffer.

Challenges

A top challenge that remains is choosing the right camera system, according to the representatives for mining companies with new froth camera systems we interviewed. “There are a number of different types of cameras on the market with quite a difference in pricing, so determining the particular style of camera to install and deciding on the company to deliver results is one of the most difficult challenges,” says Noel Moffatt, instrument and process control superintendent for Barrick’s Papua New Guinea operations. As well, for mines such as his that had no previous experience with froth cameras, it is imperative to find a supplier that can provide in-depth education on the technology. From considering the material of the brackets that hold the cameras to minimize corrosion to how they are positioned to avoid vibration or direct sunlight, careful installation is critical to both the longevity of the cameras and the quality of the images they capture.



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Customer service, says Fulton, is very important. “We have remote connection,” he explains. “So Portage can log onto our computer and fix most everything that might be wrong from Toronto. Also make sure you call their references and make sure their systems are as simple and trouble free as they say they are.”

Benefits and ROI

On average, a good froth camera system can result in about a one per cent increase in production, says Araujo. Penhorwood mine began its froth camera installation last year in mid-November. Within a couple of months, the mine was already seeing notable improvement. “It’s working better than we were expecting it to work,” says Fulton. “Basically, your production rate goes up. In our case, if we throw 100 tonnes of rock into a plant, we used to be happy with a 30 per cent yield. Now, we get 35 tonnes of product for the exact same cost.”

One of the goals the operations team at Copper Mountain had, when it upgraded its controls and froth camera systems, was to increase production consistency between shifts. With the new system, says Westendorf, the mine was able to reduce the variation in production level between crews to one percent from three or four per cent.

These days, the return on investment can be remarkably quick due to a combination of the improved technology as well as the lower costs. “While each camera can produce some 200 points of data each cycle, we currently only use 25 points of data within the controls,” says Schaffer, pointing out that research and development is ongoing and quickly developing to use more of the data collected for increasingly accurate froth management.

Watch: Michael Schaffer of Portage Technology discuss mineral processing plant optimization

Michael Schaffer of Portage Technology discusses mineral processing plant optimization




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