Following years of detailed test work in the ferrochrome sector, Multotec has successfully developed and proven a spiral concentrator that eliminates beaching and enhances recoveries in the 1 mm to 3 mm fractions of high density material.

Significantly, when compared to traditional spirals the new spiral has shown extraordinarily higher metal recoveries, even for minus 1 mm fractions in ferrochrome slag.

“Our SC25 spiral concentrator features steeper angles which facilitate the flow of material and increase separation efficiency,” says Hlayisi Baloyi, applications engineer at Multotec.

“It also widens the particle size range that can be treated by the spiral. Traditionally, spirals would struggle to efficiently treat material above 1 mm in heavy mineral applications, but this spiral can go well beyond that. The spiral has been a game changer even for the minus 1mm size range where higher separation efficiencies have been achieved on chromite ore.”

Baloyi says that this innovation has provided the minerals processing sector with an exciting alternative to jigs in the minus 3 to plus 1 size range, which have been one of the conventional methods of separating larger particles. The solution is cost effective as spirals use no electricity, and are also easy to maintain. So attractive is the new model that the first order for the commercialised version has already been placed.

“Taking ferrochrome samples from a number of mines over a period of two to three years, we conducted extensive test work on these at our well-equipped testing facility in Spartan near Johannesburg,” he says. “Leveraging this data with our in-house engineering design capacity, we were able to develop the optimal solution and locally manufacture the new spiral concentrator.”

The institutional knowledge within Multotec has been developed over more than four decades, including valuable expertise in fluid dynamics. Hands-on experience in test work and design allows the development of prototypes that solve customers’ specific challenges – followed by scaled-up local production of equipment to match market demand.

The economic benefits of the Multotec SC25 spiral for ferrochrome producers are substantial, as some plants were losing the value of their 1 to 3 mm material to the tailings storage facility. Many of those who used jigs to treat this fraction were also finding that their efficiencies were low.

“Ferrochrome is not the only commodity that we have successfully tested,” says Refentse Molehe, process engineer at Multotec. “We have even seen improved recovery in heavy minerals below 1 mm size, alluvial chrome, manganese slag and there is potential in industrial recycling.”

The recycling application opens up options for ‘urban mining’ – the recovery of metal particles from associated waste. Multotec has received a number of requests and conducted tests to recover metals from recycled electronic goods and from customers who intend to recover metal from industrial scrap.