Grindibility and breakage characteristics of Sekota iron ore deposit in Wag-Himra Zone, Northern Ethiopia
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Date
2023-06
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Addis Ababa University
Abstract
In this study, the influence of mill rotation speed and grinding time were investigated on Sekota
iron ore grinding process in a batch mill with length 150 mm and inner diameter 150 mm. The
particle size distribution of the feed was carried out by an electric sieve and the bulk feed was
classified into three samples to perform the grinding test. Three distinct iron ore feed size
fractions between -335mm to +0.71mm, -0.71mm to +0.15mm and -3.35 to -0.075mm separated
by a series of √2 gaps were prepared. The fractions were milled at different grinding times (5,
15, 25, 35, 45 and 60 min) at 450 rpm and at different mill rotational speeds (250, 300, 350, 450
and 550 rpm) at 25 min. The mill rotation speed and grinding time affect the energy
consumption, the desired grind size and the P80 of the feed size fraction. When grinding time
increased from 5 to 60 min, the percentage of cumulative mass of target size increased from 8.5
to 31.1%, from 7.1 to 22.8% and from 10.6 to 26% for coarse, fine and mixed iron ore size
fractions, respectively. Likewise, a significant amount of the desired grind size is produced as the
grinding speed increases until the maximum critical speed is reached. For all feed size fractions,
the required grind size amount (-0.075 mm) is not achieved at grinding times from 5 min to
60 min and at maximum mill rotation speed (450 rpm). The product size distribution of the three
iron ore feed size fractions were also affected as the grinding time and the mill rotation speed
increased from 5 to 60 min and 250 rpm to the maximum speed (450 rpm). The P80 values of all
feed size fraction generally decreased both milling time and mill speed are increased from 5 to
60min and 250 to 450 rpm respectively. Unlike the P80, the energy consumption of the ball mill
increases significantly as the mill speed and grinding time increase from 250 to 450 rpm and
from 5 to 60 minutes respectively.
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Keywords
Grinding, Grinding time, Mill speed, Iron ore, particle size distribution.