XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2719
As shown in Figure 4, the application of wash water
greatly reduced the silica retained in the product stream.
Operating at 3 wt.% feed solids concentration, the system
is already significantly dilute. When wash water is applied
to the upper vertical section, it becomes extremely dilute.
With a product flux of 0.31 cm/s ±0.02 cm/s, and wash
water flux at 0.83 cm/s, a bias flux of 0.52 cm/s down the
column is generated. At these conditions, the upper zone of
the cell acts as a reverse fluidized bed, generating a highly
permeable bubbly/foam flow. This condition facilitates the
stripping of bulk solids away from the rising bubbles. The
reduction in particle entrainment, whether through bubble
swarms or in the wake of rising bubbles, consequently, leads
to decreased silica yield in the presence of wash water.
The addition of NaCl appears to slightly increase the
recovery of silica in the absence of wash water. This effect
can be attributed to the salt-induced aggregation of par-
ticles, as it screens the surface charge of silica particles.
This leads to less electrostatic double layer (EDL) repulsion
between particles as shown in Figure 5, allowing particles to
come closer, with finer particles more inclined to aggregate
with larger ones. With the introduction of counter-current
washing, these aggregate particles are more likely to be
washed into the tailings. Consequently, fewer fine particles
are expected to report to the product at higher salt concen-
tration in the presence of wash water.
Zeta Potential
The addition of NaCl changes the silica particle surface
charge, as shown in the work of Romero et al. (2018). The
zeta potential of the silica particles used, was measured at
different NaCl concentrations, and presented in Figure 5.
From Figure 5, the addition of NaCl salt significantly
lowered the negative surface charge of the silica particles.
Reducing the surface charge, lowers the EDL repulsion
between silica particles, increasing the aggregation of these
particles within the thin liquid film between bubbles prior
to entering the wash zone. In the highly permeable bubbly
zone, these particles are carried away by the strong bias flux.
Bubble Size
Upon applying the Stardist code to the extracted frames,
between 519 and 9685 bubbles were measured for each con-
dition. The quantity of bubbles measured was constrained
not by any inherent limit but by the quality of the captured
video. A number distribution was generated, presented in
Figure 6. From these distributions, the Sauter mean diam-
eter was determined and subsequently determined the bub-
ble surface flux which is presented in Figure 6.
In Figure 6(A) the distinct distribution observed is for
the conditions without wash and without NaCl, where the
curve shows a secondary peak at 1.15 mm size. This sug-
gests potential bubble coalescence. The introduction of the
counter-current washing increases the fluid flow between
the bubbles, decreasing the rise velocity and establishing a
more robust separation between the bubbles. This reduced
rise velocity, along with the thicker liquid film encasing each
bubble, mitigates bubble coalescence, thereby eliminating
the secondary peak in bubble size distribution noted in the
absence of counter-current washing. Moreover, the pres-
ence of salt is known to inhibit bubble coalescence (Firouzi
Figure 5. Zeta potential of silica particles (at 0.1 wt% solids) as a function of NaCl concentration
As shown in Figure 4, the application of wash water
greatly reduced the silica retained in the product stream.
Operating at 3 wt.% feed solids concentration, the system
is already significantly dilute. When wash water is applied
to the upper vertical section, it becomes extremely dilute.
With a product flux of 0.31 cm/s ±0.02 cm/s, and wash
water flux at 0.83 cm/s, a bias flux of 0.52 cm/s down the
column is generated. At these conditions, the upper zone of
the cell acts as a reverse fluidized bed, generating a highly
permeable bubbly/foam flow. This condition facilitates the
stripping of bulk solids away from the rising bubbles. The
reduction in particle entrainment, whether through bubble
swarms or in the wake of rising bubbles, consequently, leads
to decreased silica yield in the presence of wash water.
The addition of NaCl appears to slightly increase the
recovery of silica in the absence of wash water. This effect
can be attributed to the salt-induced aggregation of par-
ticles, as it screens the surface charge of silica particles.
This leads to less electrostatic double layer (EDL) repulsion
between particles as shown in Figure 5, allowing particles to
come closer, with finer particles more inclined to aggregate
with larger ones. With the introduction of counter-current
washing, these aggregate particles are more likely to be
washed into the tailings. Consequently, fewer fine particles
are expected to report to the product at higher salt concen-
tration in the presence of wash water.
Zeta Potential
The addition of NaCl changes the silica particle surface
charge, as shown in the work of Romero et al. (2018). The
zeta potential of the silica particles used, was measured at
different NaCl concentrations, and presented in Figure 5.
From Figure 5, the addition of NaCl salt significantly
lowered the negative surface charge of the silica particles.
Reducing the surface charge, lowers the EDL repulsion
between silica particles, increasing the aggregation of these
particles within the thin liquid film between bubbles prior
to entering the wash zone. In the highly permeable bubbly
zone, these particles are carried away by the strong bias flux.
Bubble Size
Upon applying the Stardist code to the extracted frames,
between 519 and 9685 bubbles were measured for each con-
dition. The quantity of bubbles measured was constrained
not by any inherent limit but by the quality of the captured
video. A number distribution was generated, presented in
Figure 6. From these distributions, the Sauter mean diam-
eter was determined and subsequently determined the bub-
ble surface flux which is presented in Figure 6.
In Figure 6(A) the distinct distribution observed is for
the conditions without wash and without NaCl, where the
curve shows a secondary peak at 1.15 mm size. This sug-
gests potential bubble coalescence. The introduction of the
counter-current washing increases the fluid flow between
the bubbles, decreasing the rise velocity and establishing a
more robust separation between the bubbles. This reduced
rise velocity, along with the thicker liquid film encasing each
bubble, mitigates bubble coalescence, thereby eliminating
the secondary peak in bubble size distribution noted in the
absence of counter-current washing. Moreover, the pres-
ence of salt is known to inhibit bubble coalescence (Firouzi
Figure 5. Zeta potential of silica particles (at 0.1 wt% solids) as a function of NaCl concentration