FLSmidth's modular Reflux Classifier plant

Losing valuable minerals to tailings is a concern for every minerals plant, whether the result is lost profit or potential penalties from regulators.

Consequently, it is of little surprise to see a growing level of interest in fine gravity separation technologies that can offer higher recoveries than traditional solutions.

This article first appeared in Mining Review Africa Issue 4, 2019
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The development and application of know-how in fine gravity separation has been evolving for some time, and optimised technologies can deliver productivity enhancements across a range of commodities.

In addition to coal processing, these include chromite, iron ore, minerals sands, manganese, spodumene and tin – and the list is growing.

A good example is within the South African platinum sector where removing chromite from Platinum Group Metal (PGM) tailings for companies mining the UG2 seams is crucial.

Typically, the mines use flotation cells to recover PGM concentrate, but the remaining material still often contains valuable levels of chromite. In fact, head grades of up to 23% chromite in waste streams is not uncommon.

The incentive to remove the chromite is high and in this particular application the customer needed a solution that could also be used in an inter-stage duty between the primary flotation tail and secondary milling.

Chromite in itself is valuable, but is also a contaminant in the smelting process of PGMs and too much of it left behind could lead to penalties being imposed on producers.

Spirals technology has gone some way to beneficiating the ‘waste’ chromite stream but is inefficient in dealing with particles smaller than 100 micron.

It can also be unforgiving if the head grade composition changes, requiring adjustments to be made manually.

In this demanding environment, the need for a high-performance solution has long been required.

The reassuring results from the FLSmidth REFLUX Classifier (RC) means this industry demand can now be answered.

Performance data shows impressive results wherever there are differences in the specific gravity of the product and the reject material across a growing range of commodities.

“While there were several factors in play, we specifically had the UG2 market in mind when we designed the modular configuration of the RC,” says Ricus van Reenen, FLSmidth’s regional product line manager – separation.

“We had considerable interest from this commodity sector, so we decided to develop a complete RC modular plant for customers to see the potential for themselves.”

The performance of classifiers can be easily compromised, for instance where a third party wrongly specifies peripheral equipment.

But the simple ‘plug and play’ functionality of the RC modular plant means FLSmidth can accurately specify and install the correct ancillary components to meet the RCs exact needs.

Secondly, the modular solution can be installed without disrupting existing process facilities. It is set up in a suitable space on site and requires slurry feed, power feed and water supply as well as the civil infrastructure for the plant.

“Thirdly, the modular format allows for better financial and contractual offerings. While a plant can be purchased outright, we can support the customer by financing the sale and receiving milestone payments from additional operational profit” says van Reenen, “and there is also a Build-Own-Operate-Transfer (BOOT) option on the table.”

“We have even gone as far as offering an outcomes-based model, where we provide the whole solution, as well as operating and maintenance and we share in the upside of the revenue with the customer,” he adds. “We believe these financial innovations are vital at a time when many parts of the minerals sector are under enormous cost pressure.”

He emphasises that these financial offerings bring a new dimension to the minerals processing sector. It saves on the months, if not years, that companies may spend seeking funding for this kind of capital expenditure.

Confidence in the RC technology and the modular configuration has not been misplaced. He references the outcomes-based arrangement in place with a platinum mine in South Africa.

A modular plant is on site – at the tail end of a spiral plant at a platinum concentrator – and is being successfully operated by an FLSmidth team.

“We designed this modular RC plant, fully assembled and carried out FAT at our Super Centre facility, dismantled into modules, transported it to the mine and where we quickly reassembled and commissioned it. We are operating on a fixed rand per tonne of product produced basis with the customer,” says van Reenen.

“The mine supplies the material from their plant, as well as our power requirements and water, and we operate the plant to generate final product. We then receive a share of the revenue from their sale of this product stream.”

Even though the material has gone through a spirals stage of gravity separation, the RC is still able to recover significant tonnage of chromite to make the operation commercially viable.

“This confirms our sustainable productivity promise to customers, and allows them to take up a low-risk or no-risk opportunity to improve revenue by increasing overall plant yields,” van Reenen adds.

While the focus so far for the modular plant concept has been on South African applications, international interest is growing.

Two units, incorporated into a single modular plant, were recently sold to a manganese mine in Australia, where they will treat the fine fraction from the run-of-mine stream.

Test work showed the need for a different configuration in this case, so two RC units are run in parallel, splitting into finer and coarser streams.

An important benefit of RC technology is the fully automated operation.

With probes that measure the differential density of the material in the tank, the underflow valve is automatically adjusted.

The result is more consistent output, with less need for human intervention. It leaves the operator free to focus on the broader functioning of the plant.

“The control system and software for the modular plant is built in-house, and we are implementing external reporting methods through digital platforms,” he says.

“The plant manager can access the control system remotely on computer, tablet or smartphone – in real time.”

Better recovery rates are the primary value in productivity that customers will notice.

But the modular innovation, combined with the various financial options available, will make this process solution even more valuable.

The opportunity to boost mine revenues without the usual capital commitment or risk has seldom been so straightforward.

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