Spiral Test Rig solves separation challenges

Multotec Spiral

Responding to industry’s need to re-treat chrome dumps, Multotec has been adapting its versatile spiral test rig to upgrade ultra-fine chrome.

The full-scale test rig is part of a range of dedicated facilities employed by Multotec’s Technology Division to optimise mineral separation and concentration methodologies for customers. Located at the company’s headquarters in Spartan, Gauteng, the rig allows eight to 10 different spirals to be erected at a time.

“With the drive to process tailings in the chrome sector, we have been running tests on a more compressed spiral with a reduced pitch,” says Jeantelle Rust, R&D engineer at Multotec Process Equipment. “This reduces the velocity of the very fine particles.”

This configuration works particularly well when dealing with fine material, hence its application in tailings, says Rust. The spiral could offer a cost efficient way of separating ultra-fine chrome material and recovering valuable product. 

“Such a solution presents an attractive commercial proposition to industry, and will also address environmental concerns presented by tailings dumps,” she says.

Using a mouth-organ product box, the material being tested on the spiral rig is split into eight product fractions, not just the usual three for product, middlings and tailings. This helps optimise the mass balance for reporting purposes.

The spiral test rig has also been used to evolve designs that deal with coarser material. Customers were looking for a solution to the ‘beaching’ of coarse coal product on the spiral’s surface, for instance. 

“We were able to modify the angles and diameter of the trough to address this challenge,” she says. “Our ability to make small adjustments to the equipment, and to test material repeatedly at full scale, is the key to finding practical solutions.”

Multotec has also conducted research for producers of mineral sands – or heavy minerals – where head grades were steadily dropping. This necessitated the treatment of larger tonnages, requiring higher capacity spirals. 

“Space constraints on the customer’s site meant that adding spirals to their process was not an option,” says Rust. “Wider spirals were thus tested for higher throughput, with different angles to minimise losses.”

While the spiral appears to be a relatively simple piece of equipment, she highlights that the variety of forces at play makes it impossible to accurately model a spiral’s action and results. The kind of testing conducted by Multotec is therefore vital to achieve optimal separation efficiencies. 

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