XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 1153
increase, the grade initially decreases and then increases.
This is because a higher angle reduces separation time,
influenced by centrifugal force, leading particles to the tail-
ing fraction. Figure 5(b) shows that grade (%Fe) of the
concentrate fraction decreases with increased inclination
and reaches a maximum at an intermediate angle. The
grade rises with a decrease in inclination up to a point, then
declines at both higher and lower inclinations.
Figure 5(c) shows that as drum rotational speed
increases, concentrate grade decreases due to the recovery
of unwanted minerals. At lower speeds, better separation
results in higher grades. Higher speeds generate centrifugal
forces on both heavy iron ore and coarse lighter particles,
increasing iron recovery but reducing grade, as the compact
fine particle bed resists wash water effects. Figure 5(d) indi-
cates that with lower wash water flow, grade continuously
decreases as drum speed increases. At higher flow rates,
grade increases up to 200 rpm, then decreases.
Effect of Process Variables on Recovery (Weight %)of
Concentrate Fraction
Eq. 3 models the estimation of the recovery (%Fe) of the
concentrate fraction. The main effects—drum rotational
speed, angle of inclination, and the squares of wash water
flow and drum speed—significantly impact separation.
Among interaction effects, the angle of inclination and
wash water flow rate notably affect recovery. However, the
angle of inclination, wash water flow rate, and their inter-
action with drum speed are less significant. The empirical
models, used to describe the impact of these variables in
various combinations on recovery, are shown in Figure 6.
The effect of angle of inclination and wash water flow
rate on concentrate recovery at the central drum inclina-
tion is shown in Figure 6(a). Higher concentrate recovery is
observed at both low and high drum inclinations and wash
water flow rates. Recovery initially decreases to a certain
point and then increases.
Figure 6(b) illustrates the impact of wash water flow
rate and drum inclination angle on the recovery of the con-
centrate fraction in MGS. Initially, as wash water flow rate
increases, recovery decreases and then rises for both lower
and higher inclination angles.
Figures 6(c) and 6(d) depict the impact of drum rota-
tional speed on concentrate recovery at different inclina-
tion angles and wash water flow rates. Figure 6(c) shows
that maximum recovery occurs at higher drum speeds and
greater inclination angles, with a slight effect at lower wash
water flow rates. Higher drum inclination yields better
recovery, and increasing drum speed boosts recovery at
higher inclinations. Changes in recovery with varying incli-
nation are minimal at higher drum speeds.
Figure 6(d) shows that as drum rotational speed
increases, concentrate recovery also increases across differ-
ent wash water flow rates. Notably, recovery is higher at
lower wash water flow rates compared to higher ones.
CONCLUSION
Iron values from sub-grade iron ore can be recovered
by optimizing process parameters of the Multi Gravity
Separator (MGS). This study considered three key param-
eters: drum inclination, wash water flow rate, and drum
rotational speed. Mathematical models for both grade and
recovery of iron in the concentrate fraction were developed
using experimental data and the Minitab 16 software.
Using the Box-Behnken method and Response Surface
Methodology, the study investigated the effects of drum
inclination, wash water flow rate, and drum rotational speed
on the MGS. The goal was to predict the grade and recov-
ery of iron concentrate from sub-grade iron ore (SGIO).
Mathematical model equations for grade and recovery were
derived using experimental data and Minitab 16.
Drum rotational speed significantly influenced both
grade and recovery in the Multi Gravity Separator (MGS),
with optimal levels determined through quadratic pro-
gramming for maximum grade and recovery. The highest
grade of 62.21% Fe was achieved at 198 rpm, 4.3° inclina-
tion, and 2.7 LPM wash water. Similarly, the highest recov-
ery of 65.37% by weight was obtained at 212 rpm, 4.3°
inclination, and 2.6 LPM wash water. These models effec-
tively explained the impact of these parameters on MGS
performance for treating sub-grade iron ore (SGIO), with
predicted values closely matching experimental results (R2
values of 0.97 and 0.99 for recovery and grade, respectively).
This study proved that Box–Behnken design, response
surface methodology could efficiently be applied for mod-
elling of sub grade iron ore from Bailadila and that it is
economical way of obtaining the maximum amount of
information in a short period of time and with the fewest
number of experiments.
ACKNOWLEDMENTS
The authors wish to thank Management of NMDC Limited
for approval to conduct studies and permitting to publish
this paper. The support and services provided by staff of
R&D Centre are also duly acknowledged.