Change from pressure crushing in roller mills to impact crushing in production of mineral sand

North Cape Minerals operates a nepheline syenite mine, delivering raw mater ials to glass and ceramic producers all over the world. Removal of unwanted minerals is done dry. Most of the production is delivered as Altafloat wit h a particle size defined by d(99,9) = 500 mu m and d(8) = 74 mu m. This re quires a comminution circuit which does not produce excess fines. Originall y, roller crushers in closed circuit with screens were used for this purpos e. This operation was continuously improved over 30 years but there were 20 parallel units and too much maintenance. After 3 years of testwork, it was therefore decided to replace the roller crushers by Barmac crushers. This has resulted in a slightly higher production of fines, but operation is muc h simpler and more economical partly because the feed size for fine crushin g is increased from -8 to -12 mm. (C) 1999 Elsevier Science S.A. All rights reserved.