XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2065
feed material, the operational parameters, and the separa-
tion efficiency of the spiral concentrator. Magnetite being
the heavier mineral will primarily concentrate in the inner
zone and its size range typically falls within the coarser
fraction, ranging from 1 to 100 µm (coarse sand to fine
sand). Silica due to its lighter density, these particles will be
excluded from the inner zone. However, some very fine and
liberated silica particles (less than 50 microns) might still
be entrained with the coarser magnetite due to the agglom-
eration. Heavier and coarser particles experience stron-
ger gravitational and centrifugal forces, propelling them
towards the inner zones. The outer zones contain mostly
finer particles with sizes less than 100 microns. Smaller
concentration of magnetite particles will be lost here due to
inefficient separation of finer particles. Silica will be more
concentrated at a major fraction in this outer zone. The
size range can vary widely depending on the original feed,
but typically includes particles lesser than 50 microns. The
weaker gravitational and stronger centrifugal forces acting
for finer and lighter particles, dominates and push them
towards the outer edge.
The feed with pure magnetite and silica when pro-
cessed in the spiral concentrator separately at 4 m3/h, the
average particle size of the collected magnetite progressively
shrinks, from the innermost Zone 1 towards the outer
Zone 5 (Figure 4). Unlike magnetite, the average parti-
cle size of silica follows a increasing and decreasing trend
rather than a sharp declining trend towards the outer zones
(Figure 5). Zone 1, close to the central column, the weak
centrifugal force has minimal impact on even the largest
silica particles.This trend can be attributed to a dynamic
interplay of forces within the spiral, primarily driven by
hydrodynamics and gravity. Zone 1, which corresponds to
the concentrate region near the central column, experiences
the particle collisions, interlocking and agglomeration,
which can influence the segregation pattern of the parti-
cles and decreases the average particle size. The finer silica
particles accumulate within the coarser particles, and this
becomes evident during size distribution. In zone 1, from
Figure 5, the average particle size (D50)of the magnetite is
the largest at 39.49 µm while the D50 of silica is 40.1 µm,
relatively large compared to magnetite.
Zone 1 experiences strong gravitational force and con-
centrates larger and denser particles towards the center of
the spiral. In zone 2, the D50 of magnetite decreases to
34.87 µm as the gravitational force weakens slightly. The
D50 of silica increases to 48.8 µm as the coarser particles
begin to accumulate and the declining trend starts from
hereafter. Further into zone 3, the D50 of magnetite reduces
to 27.07 µm, suggesting the concentration of finer-sized
magnetite particles and the D50 of silica also decreased
to 44.7 µm,. In zone 4, the D50 of magnetite drops sig-
nificantly to 18.48 µm as the centrifugal forces dominate,
allowing finer particles to settle, while the D50 of silica sig-
nificantly reduces to 24.16 µm .Finally, in zone 5, located
at the outer edge and representing the tailings region, the
D50 of magnetite is the smallest at 16.07 µm and 18.65 µm
of silica. This is attributed to the strongest centrifugal force
in zone 5, resulting in the majority of finer-sized magnetite
particles being directed towards the tailings.
From the Figures 6, it is observed that the average par-
ticle size for both magnetite and silica in feed proportions
Figure 3. Particle size distribution of silica and magnetite in the feed
feed material, the operational parameters, and the separa-
tion efficiency of the spiral concentrator. Magnetite being
the heavier mineral will primarily concentrate in the inner
zone and its size range typically falls within the coarser
fraction, ranging from 1 to 100 µm (coarse sand to fine
sand). Silica due to its lighter density, these particles will be
excluded from the inner zone. However, some very fine and
liberated silica particles (less than 50 microns) might still
be entrained with the coarser magnetite due to the agglom-
eration. Heavier and coarser particles experience stron-
ger gravitational and centrifugal forces, propelling them
towards the inner zones. The outer zones contain mostly
finer particles with sizes less than 100 microns. Smaller
concentration of magnetite particles will be lost here due to
inefficient separation of finer particles. Silica will be more
concentrated at a major fraction in this outer zone. The
size range can vary widely depending on the original feed,
but typically includes particles lesser than 50 microns. The
weaker gravitational and stronger centrifugal forces acting
for finer and lighter particles, dominates and push them
towards the outer edge.
The feed with pure magnetite and silica when pro-
cessed in the spiral concentrator separately at 4 m3/h, the
average particle size of the collected magnetite progressively
shrinks, from the innermost Zone 1 towards the outer
Zone 5 (Figure 4). Unlike magnetite, the average parti-
cle size of silica follows a increasing and decreasing trend
rather than a sharp declining trend towards the outer zones
(Figure 5). Zone 1, close to the central column, the weak
centrifugal force has minimal impact on even the largest
silica particles.This trend can be attributed to a dynamic
interplay of forces within the spiral, primarily driven by
hydrodynamics and gravity. Zone 1, which corresponds to
the concentrate region near the central column, experiences
the particle collisions, interlocking and agglomeration,
which can influence the segregation pattern of the parti-
cles and decreases the average particle size. The finer silica
particles accumulate within the coarser particles, and this
becomes evident during size distribution. In zone 1, from
Figure 5, the average particle size (D50)of the magnetite is
the largest at 39.49 µm while the D50 of silica is 40.1 µm,
relatively large compared to magnetite.
Zone 1 experiences strong gravitational force and con-
centrates larger and denser particles towards the center of
the spiral. In zone 2, the D50 of magnetite decreases to
34.87 µm as the gravitational force weakens slightly. The
D50 of silica increases to 48.8 µm as the coarser particles
begin to accumulate and the declining trend starts from
hereafter. Further into zone 3, the D50 of magnetite reduces
to 27.07 µm, suggesting the concentration of finer-sized
magnetite particles and the D50 of silica also decreased
to 44.7 µm,. In zone 4, the D50 of magnetite drops sig-
nificantly to 18.48 µm as the centrifugal forces dominate,
allowing finer particles to settle, while the D50 of silica sig-
nificantly reduces to 24.16 µm .Finally, in zone 5, located
at the outer edge and representing the tailings region, the
D50 of magnetite is the smallest at 16.07 µm and 18.65 µm
of silica. This is attributed to the strongest centrifugal force
in zone 5, resulting in the majority of finer-sized magnetite
particles being directed towards the tailings.
From the Figures 6, it is observed that the average par-
ticle size for both magnetite and silica in feed proportions
Figure 3. Particle size distribution of silica and magnetite in the feed