Magnetic collection of grinding ball fragments from SAG and ball mill circuits

Grinding ball fragments discharging from SAG mills and ball mills causes extreme wear to downstream processing equipment. These bail fragments, recirculating in a milling circuit, will cause excessive wear to sumps, pumps, hydrocyclones, and interconnecting piping. A magnetic separation system to remove grinding ball fragments from the mill discharge has been developed and successfully applied in the milling circuit. This magnetic separation system - termed Trommel Magnet - was first applied at the Escondida copper concentrator in Chile. The Trommel Magnet consists of an are of permanent magnets mounted at the discharge end of the trommel screen. The magnetic are attracts the ball fragments and removes them from the process stream. This retrofitted magnetic separation system removed 126 metric tons of ball fragments from the circulating load of a single ball mill in the initial 24 hour period. The mill has since stabilized and the magnetic separator is currently removing 7 metric tons per day of ball fragments. The retrofit of the Trommel Magnet has: 1. Extended the pump life and the hydrocyclone life approximately 300 percent. 2. Provided a 5 percent increase in the throughput of the mills by removing grinding ball fragments that contribute very little to the grinding process. Variations of the Trommel Magnet have also been developed for removing grinding ball fragments directly from the mill discharge without the use of a trommel screen. In each case, permanent magnets are used to collect the ball fragments from the mill. discharge stream prior to reporting to the sump. These other systems have been designed and fabricated for in-plant test work.