By Dr Mark Cooksey

Can the efficiency of slurry mixing tanks be optimised?

Slurry mixing tanks are vital to the processing and refinement of ore bodies. The chemical reactions that they facilitate situate them in a series of processes that comprise the backbone of the mining industry; the generation of revenue and development of quality products relies on them.

Despite their huge importance to the refining processes and their worldwide usage, there is room for improvement. Currently, slurry mixing tanks can suffer a number of hindrances to their performance:

• agitator mechanical failure
• wear from erosion
• sedimentation build-up
• scale build-up
• bogging of tanks.

These inefficiencies can cause massive downtime, and are also incredibly costly to fix. This poses the risk of budget blowouts due to unplanned maintenance.

So given this, have you considered taking the next step and upgrading your slurry mixing tanks?

Impeller placement, optimised maintenance: potential improvements to slurry mixing tanks

Impellers placed low in a tank pose the biggest opportunity for optimisation, as scale formation or coarse particle segregation builds up inside the tank from the bottom-up.

So the impeller, in its current position, quickly begins to meet resistance.

As such, the scale build-up causes the impeller to experience detrimental impacts to its performance. This leads to one of two scenarios:

1. The slurry mixing tank continues to be used, with a reduction in the mixing ability and efficiency.
2. The tank must be shut down and the arduous process of cleaning it out must begin. This causes extensive delays and downtime in the refinement process.

On top of this, the placement of the impeller near the bottom means that it comes into contact with an extensive amount of solid matter, causing it to wear and deteriorate.

So on top of being incredibly difficult to clean the blades, they can also need frequent (and expensive) replacement.

The need for upgraded slurry mixing tanks

Slurry mixing tanks are currently very hard to optimise; by their nature even if you are doing everything right, they are still going to lead to excessive costs. Significant downtime and maintenance costs are usually considered inevitable.

One of the world’s leading alumina producers saw this problem first hand, as they found that the their slurry mixing tanks were suffering major inefficiencies due to excessive bogging. They realised that they needed a fix that would allow them to work at their current speed but without the extensive maintenance costs.

While they acknowledged the essential need for a faster repair process, they also had an intense need for a reduction in scale formation. Ultimately slurry mixing tank optimisation had become a top priority, as a seemingly insignificant part of the refining process was swiftly becoming a huge drain on resources.

Optimise slurry mixing tanks with Swirl Flow: a tornado in a tank

When you’re looking to optimise your slurry mixing tanks, it would seem that there is seemingly no easy way to achieve this. Fortunately, improving the impeller is now possible.

CSIRO has developed Swirl Flow — a way to simplify and improve the agitation process by mixing liquids and suspended solids, to create a “tornado in a tank”. Swirl Flow places a single impeller at the top of the tank, making it much easier to clean and preventing erosion to the blades through a reduction in contact with solids.

Swirl Flow optimises slurry mixing tanks in the following ways:

• reduction in breakage-related shutdowns — the better placement of blades causes a reduction in deterioration
• reduction in scale build-up — due to higher and more uniform wall velocities
• optimised cleaning and maintenance — the new impeller placement means never having to extract it from the bottom of the tank, and
• cheaper maintenance —Swirl Flow, due to its reduced weight and size, requires a less powerful motor, and is therefore lower cost.

After retrofitting their leach tank with Swirl Flow, leading alumina providers have seen a dramatic improvement to their efficiency, increasing online time from 3-4 months to more than 12 months.

This solution is simple and inexpensive to retrofit to existing tanks. By implementing this seemingly insignificant improvement across your operation, you could potentially save millions in improved productivity.

The Fluids Engineering team at CSIRO, through our research and breakthrough science, is uniquely positioned to add value to your operation. Through process improvement assessment, modelling, designing and deploying new technology, we can help you solve your mixing challenges to optimise your operations.

Contact the Sustainable Metals team on +61 3 9545 8865 or email me, Mark.Cooksey@csiro.au, to discuss how our expertise and experience can help you.

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