HomeFeatures & AnalysisMultotec spirals improve recoveries, grades and yields

Multotec spirals improve recoveries, grades and yields

The decision to replace the existing spirals with those designed and manufactured by Multotec was taken by this chrome producer following extensive test work performed by both Northam Chrome Producers and Multotec.

Results from the test work performed at Northam Chrome Producers revealed that Multotec’s spirals outperformed the competitor units originally installed in the plant. Testwork was later revalidated at Multotec’s in-house technology division in Spartan, Gauteng, South Africa by Faan Bornman, technology manager.

Based on the outcome of these trials, Northam Chrome Producers decided to replace the existing spirals, which had reached their end of life, with Multotec spiral technology. “Tests showed that by using the Multotec spirals, the plant would be able to increase recoveries by an additional yield of 6%,” says Multotec’s Graeme Smith.

Smith says Multotec was tasked with removing 172 spiral assemblies from Northam Chrome Producers’ existing recovery plant and replacing these with 72 Multotec spiral assemblies. These comprised Multotec HX5 and Multotec HX3 spirals with feed tonnage capacities ranging from 4 tph to 9 tph per start.

He says one of the biggest challenges of the eight-week long project was retrofitting the new spirals into the existing structure. Extensive work was done by Multotec’s in-house drawing office, which undertook all the drawings and confirmed the new layout of the plant, while also presenting the modifications needed to the structure to accommodate the new installation.

The project was overseen by Smith and field service technician, Raymond Masinga. “The commissioning of the plant was an easy exercise. It started up the same day and immediately started outperforming the earlier test results,” Smith says. He reports that the entire plant’s yield is now closer to 30%, compared to the average of 21% in 2014.

Multotec engineers have ascertained that the cost of the spiral assembly is about 0.004c/feed ton, with Northam Chrome Producers expected to see a return on its investment within a four year period.

The plant was commissioned in February 2015 and, at the time of writing the installation had been running from the end of December that year to mid-February 2016.

In progress retrofit installation of Multotec HX3 spiral bank in a custom designed frame to suit the existing spiral building structure
In progress retrofit installation of Multotec HX3 spiral bank in a custom designed frame to suit the existing spiral building structure

Smith says it is encouraging to hear from Northam Chrome Producers’ personnel based at the operation that the assembly has sustained its performance over the past 12 months.

“We have increased the plant recoveries by 6% of additional yield. The customer has been very happy with the project overall, and we are engaging with Northam Chrome Producers on another large project,” Smith says.

Multotec is currently testing the performance of its own cyclones at the plant with the intention of replacing the existing units, which have also reached the end of their life.

Smith says based on the feedback the company has received from many of its customers, Multotec has the best performing spirals in the market in fine and heavy minerals applications.

He attributes the success of the performance of these large 1 m diameter spirals to their optimised feed-in angle.

They were originally designed as a rougher and scavenger spiral to handle material ranging from 800 micron to 38 micron. “Such is their reputation in the international mining sector that a prominent iron ore miner wants to test them at one its flagship operations. Here, they will be used to recover fines ranging from 80 micron to 75 micron,” Smith says.

The success of the performance of the plant at Northam Chrome Producers has also seen it turn to Multotec to help boost recoveries even further. He reports that work has already started on designing an extra stage in the existing plant to bolster recovery yields by up to 9%.

Another important aspect of this project is that this is the first time that Multotec’s pipe launder systems have been used in a chrome application. This well-engineered system has been well received in mineral sands and iron ore applications due to the very high wear resistance characteristics.

Unlike their steel competitors, the pipes are made from uPVC and PU lined, materials well-known for their resistance properties, boosting the lifespan of the pipes by up to nine times, according to Smith. They are also lighter than their steel counterparts making them much easier to handle on site in maintenance applications.

“Two people can replace the pipe without the need for any lifting equipment on the small diameters. This is complemented by their polyurethane boot, which can be replaced in as little as five minutes every two to three years, depending on the application,” he says.

All the steel pipes at Northam Chrome Producers were replaced with Multotec’s launder solutions as part of the overall installation. This was a very complex undertaking as each pipe was custom engineered and manufactured to meet the individual applications within the existing plant footprint.

Multotec definitely has another happy customer in the mining industry to add to the long list of successful projects it has undertaken over the years.