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Technical
Note Effect of ball size change on
the performance of grinding and flotation circuits
At the Sarcheshmeh copper mine 41,000 t of ore per day with an average grade
of 0.9% Cu is ground to 70% passing 75 microns. Grinding is effected in 8
parallel lines of 8x5m ball mills in a closed circuit with cyclones. The
make-up balls are 80-mm forged alloy steel balls and the average ball
consumption is 750g/t of ore ground. In order to optimize ball size
distribution inside the mill, based on the previous investigation instead of
using only 80 mm make-up balls a combination of 80 and 60mm (75% to 25% by
weight) ball charge was used in one of the mills. To evaluate the
performance of three ball types namely forged alloy steel balls (A), ductile
cast iron (C), high chromium cast iron (D) and also a combined (80 and 60
mm) charge of forged alloy steel balls (B), four identical parallel mills
were charged accordingly. These four mills were sampled during a period of
one year. The amount of material finer than 75 microns of cyclone overflows
was selected as a criterion for the performance evaluation. It was observed
that in a mill with the combined make-up balls the amount of fine produced
was 4% higher than the other mills. The consumption of ball types A, C and D
were 730, 710 and 534g/t, respectively. The results of laboratory flotation
tests showed that due to an improvement in the production of fines an
increase of 1.4% in the overall copper recovery is obtainable. Due to the
promising results, the new make-up ball regime was implemented in all mills
in the plant. |
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