Gravity concentration is one of the oldest forms of mineral processing, and yet the optimization of this process continues to improve in the present age. Less than two decades ago, we presented a paper describing the placement of enhanced gravity machines within a grinding circuit and demonstrating an increase in gold production while keeping plant throughput constant.

Much has happened in the last couple of decades, to say the least!

At Sepro we have continued to innovate and create new equipment, better processes, and more optimized ways to help you make the most out of your operation.

Here’s a quick run through the past, present and future developments for one of the world’s oldest and yet still highly effective forms of mineral processing.

Benefits of Gravity Concentration

Let’s start with the basics. Why perform gravity concentration at all?

There are a multitude of benefits to gravity concentration over other forms of mineral processing such as jigging. For example, operators that have installed Falcon Concentrators enjoy these benefits:

  • Better Cash Flow via Faster Payment
    • Gold recovered from copper concentrate can be smelted into doré on site and then shipped to a refinery for immediate payment
  • Greater profits through Higher Payment
    • Gold shipped as doré will attract almost 100% of the spot price for gold whereas gold contained in concentrate attracts less, typically by 3-5%. 
  • Better Measurability through Homogeneous Samples
    • Operations that ship base metal concentrate may be taken advantage of by receiving smelters, who often benefit from variable gold content. Removing free gold before shipment makes the metal much more homogeneous and easier to sample for payment.
      • A discrepancy between what the mine thought it was sending, and the smelter was willing to pay for can amount to more than $1million USD.
  • Better Gold Recovery by Reducing Losses
    • Overall recovery can be increased by reducing losses to cleaner flotation tailings via the Falcon Concentrator treating the rougher flotation concentrate.

Optimizing Gravity Concentration

Now that we’ve gotten the basics out of the way, let’s talk optimization.

Some might think that merely installing a gravity concentrator on site would result in the best results for your mine, but the reality is more nuanced.

The benefits of using a centrifugal field to concentrate both coarse and fine ore are well-documented. However, the placement of the machines within grinding circuits is constantly evolving.

Conventional wisdom suggests that the best location for enhanced gravity machines is cyclone underflow. Yet, plant operating experiences at both large and small scale indicate that there are many benefits to placing enhanced gravity machines on cyclone feed instead.

At Sepro, we have the knowledge and experience to help you challenge the status quo to deliver the best results from your operation.

Why place enhanced gravity machines on cyclone feed?

When a cyclone overflow contains dense mineral such as electrum or free gold, it is possible to concentrate it using enhanced gravity concentration technology. Here are two examples of this placement improving total gold production.

At Echo Bay’s Kettle River Mine, the operators reported a production increase of approximately 3,000 ounces per year while maintaining cyanide consumption at baseline levels.

In another example, Newcrest Mining of Australia introduced enhanced gravity concentration to treat flash flotation concentrate at the 50,000 tpd Cadia Mine in Australia in 1997. This flash flotation concentrate was then treated with a Falcon Concentrator, where the resulting gravity concentrate was upgraded for smelting on a shaking table. This circuit would then produce upwards of 40,000 ounces per annum. The excellent performance of this circuit was discussed in a Paper by Robert Dunne of Newcrest and André Laplante at the 2002 CMP meeting.

Placing enhanced gravity machines on cyclone feed can result in significant benefits to your operation. To see if this circuit would work well for your operation, you can contact one of our mining engineers to learn more.

The Next Frontier of Gravity Concentration

In this article, we’ve established that procedural changes in placement and processes can significantly improve the effectiveness of gravity concentration. In addition to the placement of the concentrators, the machines themselves can be optimized and improved with proper research.

In 2022, Sepro will be revealing the new Frontier Bowl which is a better centrifuge bowl that brings a 30% increase in gravity gold recovery. The Sepro Frontier Bowl will soon be installed on all Falcon gravity concentrators and can also be retroactively fitted to older Knelson concentrator models.

This new centrifuge bowl has gone through rigorous testing, with results exceeding our initial expectations. Expect to learn more about the Frontier Bowl in the months to come!

Closing Thoughts

We’ve discussed the basic benefits of gravity concentration, some opportunities to improve performance based on placement, and the opportunity to significantly improve performance with better equipment.

There is still much to uncover about enhanced gravity concentration, and at Sepro we are dedicated to performing the R&D necessary to unlock the next form of optimization.

As environmental regulations and permitting requirements become more stringent, enhanced gravity concentration may become the only economically viable technology for some ore deposits. As we progress forward into 2022, we expect to see new innovations to further optimize this tried-and-true mineral processing technique.

Here’s to the next Frontier of enhanced gravity concentration!