Berzelius Stollberg placed an order for two RS12 Rotaspirals in November 2001. The units were recently commissioned for classification of granulated slag from the QSL lead furnace. The Rotaspirals remove fines below 300 microns, and also dewater the oversize.


The Rotaspirals receive a slurry feed from a quench sump using a vertical centrifugal pump and an automated mobile gantry. More than 80% screening efficiency is achieved. Discharge of oversize to a conveyor belt is managed by use of a drain section and compressed air for screen drying.

Rotaspirals were developed to provide economic fine screening using precision stainless steel mesh cloths, with a unique tension system. The rotating drum frame ensures that fresh cloth is presented to the feed slurry. An internal spiral and high pressure sprays provide fluidisation of the screen bed. Sprays and air jets are also used for reverse cleaning. Maintenance and power costs are extremely low. Rotaspirals were designed by PSS in South Africa to address high capacity problematic fine screening applications. Typically, mixed gravity particulates challenge hydraulic classifiers because of the misplacement of heavy fine particles, and light coarse particles leading to poor efficiency. High frequency vibrating screens can be more accurate, but tend to be noisy, require high maintenance and power, and performance deteriorates with wear.

PSS have installed the Rotaspiral in South Africa for removing fine chromite from platinum mill circuits.