Processing of China Clays Using a Commercial-Scale, Conduction-Cooled Superconducting Magnetic Separation System

Processing China Clay to increase its brightness is commercially important for the ceramics and paper industries. Quantum Design, Inc. has developed a high throughput conduction-cooled superconducting magnetic separation system which operates at 6 Tesla with a 10% uniformity over 406 mm. This long uniformity range, along with its 203 mm diameter bore and high magnetic field result in a single system capable of processing 10,000-15,000 tonnes of clay per year. This superconducting magnet is maintained at low temperature using a variable frequency driven Gifford-McMahon refrigerator, which dramatically reduces operating costs compared to a liquid helium cooled magnet ($40 to cool down at $0.10/kWhr). Furthermore, the small footprint of the system combined with the inexpensive operating costs allow for a modular design for systems to be combined specific to the needs of the China Clay mining facility. Testing has been carried out using various types of China Clay, also known as kaolin, from three different mines. Typical results show a reduction in Fe₂O₃ by over 60%. In particular, before processing, one sample contained 0.85 wt% Fe₂O₃ and a fired brightness of 88%. After processing in the Quantum Design SHGMS (Superconducting High-Gradient Magnetic Separator), the Fe₂O₃ content was reduced by 65% to 0.29 wt%, and the fired brightness increased to 92.5%, resulting in a three-fold increase in the value of the clay.