The Rotaspiral TM Fine Screen is a new development in fine screening technology, which may be reminiscent of trommel screens of previous times. There are, however, significant differences in design and application. During March 2002, Maelgwyn Mineral Services (MMS) delivered two Rotaspirals to Berzelius Stolberg GmbH of Germany to separate fines from granulated slag in the lead smelter. Feed rate to the parallel Rotaspirals (model RS12 with 1.1 kW drive) is between 10 and 15 t/h each. The QSL furnace at Stolberg produces granulated slag with a particle size of less than 2 mm with about 10% minus 250 micron.
The fines have an economic metal content and this portion can be profitably recycled to the smelter. It was thought that vibrating screens would not perform well in this application. Alternatively, hydro-separators were not able to provide a clear cut, recovering too many coarse particles with the fines because of gravity and shape effects. This would have resulted in recycle of nearly 30% of the slag instead of the target of less than 10%.
MMS have recently started marketing Rotaspirals, which were developed by PSS in South Africa initially for platinum mineral processing. The design of the Rotaspiral allows cut points down to 100 micron. The unique woven stainless steel mesh specification is designed to maintain clean and precise apertures. Recovery of fines is high and wear rates will be negligible because of the low velocities between mesh and particles. An axial spiral inside the screen provides transport of the oversize, and high velocity sprays at multiple points guarantee a sharp separation. Additional benefits of this technology include the low energy demand and negligible noise levels.