MechChem Africa July 2019

MechChem Africa visits the South African manufacturing facilities of Multotec’s Gravity Separation division and talks to the unit’s general manager,Wynand Erasmus, about spiral technology and the company’s latest product enhancements. Gravity concentration and SA’s spiral specialist

G ravity Concentration forms part ofMultotec’smining andminerals processing equipment offerings, alongside Samplers; Magnetic Separators; Cyclones; and Industrial Slurry Pumps. “I manage the Gravity division, which specialises mostly in spiral separation and concentration equipment,” says Multotec’s Wynand Erasmus. “As a South African processing original equipment manufacturer (OEM), we are the leading supplier of spirals to the coal and chromium industries. Spiral concentration technology is a cost effective way of separat- ing materials according to density, particle size and shape. As no moving parts are in- volved, the equipment used is robust andvery reliable,” he tells MechChem Africa . Breaking down how spirals work, he says material, generally sized at -1mm, is mixed in a solids towater ratioof about 35%. The slurry is fed via distribution systems at a controlled rate into the top of a bank of spirals that usually contains between two and 12 spiral separators. The slurry flows under gravity down the spiral. The rotating motion of the flow cre- ates centrifugal forces on the slurry causing the suspended light and low-density particles to be displaced away from the spiral’s centre column and up the side slope.

Wynand Erasmus, general manager for Gravity Separation at Multotec. concentrate (heavies), near density material (middlings) and the lighter tailings on the out- side.Multotec can add a fourth super concen- trate off-take, depending on the application. “We can shave off a super concentrate from the innermost channel, for example, which can be directed away for final processing,” says Erasmus. Although conceptually simple, spiral de- signs differ fromore toore and efficient sepa- ration of the different ore grades depends on careful optimisation of spiral diameter, the turns, pitch and profile. “Our biggest spirals have a 1.0 m diameter, while our smallest is 680 mm. We manufacture spirals with three to 12 turns, which offer much better reten- tion times and, therefore, better separation efficiencies,” he adds. Coal and the new SX10 Describing some of Multotec’s recent devel- opments in spiral separation, Erasmus first lifts out the new10-turn coal spiral, the SX10. “We are getting a really lowdensity cut of be- low1.5with this spiral, which is exceptionally good. This makes an ideal material for coking applications in the steel smelting industry,” he tells MechChem Africa . The South African coal industry currently uses Multotec’s SX4, SX7 and MX7 spirals, with tailings, middlings and concentrate splitter darts, “but the new SX10 spiral with tailings, middlings, concentrate and super concentrate darts can deliver a product with lower silica, which reduces the ash content on combustion.” Chrome fines “We are also very excited about the develop- ment of our new ultra-fine spiral, which uses a customised pitch and profile to allow more effective separation of finer particles,” he continues. “Ourtestinghasdeliveredexcellentresults on the recovery of ultra-fine chromite from UG2 platinum tailings,” he says. “We are hop- ing to move towards commercialising this technology very soon.” UG2 circuits involve the reprocessing of the ultra-fine tailings from the platinum

Heavier and more dense particles tend to sink to the working surface of the spiral, where drag and friction forces slow them down. The slower speeds mean they are sub- jected to lower centrifugal forces. As a result, heavier particles tend to follow a downward path closer to the centre of the spiral. “More dense particles take the inside path, while lighter less dense andmore easily suspended particles get spread across the outside path,” Erasmus explains. “At Multotec, we design and manufacture spiral-basedgravityconcentrationtechnology solutions for all major minerals as well as for specialised niche applications. In addition, we manufacture slurry feed distributors, laun- der systems and spiral accessories. We also produce test units to optimise and improve concentration efficiency for existing and new processing plants,” he says. “We feed individual units at feed rates from as little as 1.5 tph through to 7.5 tph on wider diameter units. Multiple spiral stages arecoupled together to raise the grade of the concentrate and to recover as much of the mineral product as possible. Chromium, copper, cobalt, tin and mineral sands such as ilmenite, rutile and zircon are all dense/heavy ores that will flow down the inside path. A spiral has three dart splitters at its base which cut the product or

Multotec spirals manufactured in South Africa with more than 60% local content verified.

24 ¦ MechChem Africa • July 2019