ADAM MCELROY1, MALCOLM POWELL2, JAN TILLBERG1, MARKO HILDEN2, MOHSEN YAHYAEI2, MATTI LINNA3 & ANNA JOHANSSON3
2University of Queensland Julius Kruttschnitt Mineral Research Centre (JKMRC)
The new Aitik autogenous grinding (AG) milling circuit was based on the successful original milling plant at Aitik, with a focus on low life-of-mine operating costs. At the heart of this is eliminating steel grinding media, maximizing the use of gravity flow, and using spiral classifiers instead of hydrocyclones. The two 22.5 MW AG mills, 11.6 metres (m) (38 feet [ft]) diameter by 13.7 m (45 ft) long, are the largest mills by volume operating in the world. Each AG mill feeds a 10 MW pebble mill via a unique coupling of flow and pebble feed with the pebble mill product recycling to the spiral classifier that is closed with the AG mill. The massive size of the AF circuit and unique layout make this an interesting case study in alternative plant layout and operation compared to the strong trend towards finer feed, high ball load and multiple ball mills per semi-autogenous grinding (SAG) mill. Operating capability, data on specific energy, throughput, and plant stability are presented as a comparative case study.
Autogenous milling, pebble mill, spiral classifier, grindcurves, energy efficiency