XXXI International Mineral Processing Congress 2024 Proceedings/Washington, DC/Sep 29–Oct 3 2429
Estimation of the Effective Collection Residence Time
in a Mechanical Cell
The main opportunity for an efficient particle-bubble con-
tact occurs when pulp circulates through the impeller zone
(Arbiter, 2000). In general, previous studies agree that the
collection process (particle-bubble aggregate formation)
mainly occurs in a zone around the impeller in mechani-
cal cells (Savassi, 2005 Amini et al., 2016 Mesa, 2020).
Further, a quiescent zone normally exists below the pulp-
froth interface, which typically has a lower pulp density,
promoting gangue segregation due to lower energy dissipa-
tion for particles collection (Savassi, 2005 Boeree, 2014
Mesa, 2020). This condition is required because it allows for
building a distinctive pulp-froth interface in order to pre-
vent the flooding condition and fine particles entrainment
into the concentrate (Yianatos and Henríquez, 2007a).
According to the previous understanding, the following
section presents a first estimation of the collection residence
time based on industrial data (Yianatos et al., 2008). In this
case, the hydrodynamic characterization of a self-aerated
mechanical cell of 130 m3, allowed for the identification
of the residence time the pulp spend in the impeller zone.
For this purpose, measurement of the pulp and air flowrates
circulating through the impeller, allowed for the estimation
of the active collection time.
Number of Circulations Through the Impeller in a Self-
Aerated Mechanical Cell
The study on the mixing characteristics in a single self-aer-
ated flotation cell of 130 m3, with a mean pulp residence
time of 5.0 min, showed that the time for a complete pulp
circulation through the impeller was around 1.0 min and
on average, the number of pulp circulations through the
impeller was five. In this case, a Flotation Number NF
to account for the mean number of particle circulations
through the active collection zone (high probability of col-
lection) was defined (Yianatos et al., 2008). In addition,
measurements of gas holdup using the radioactive tracer
technique showed that the main gas holdup occurs in the
upper half of the cell, indicating that the active collection
zone is smaller than the total pulp volume (Yianatos et al.,
2010b).
Time of Pulp Circulation Through the Impeller Zone
The 130 m3 self-aerated cell has an impeller around 0.8 m3,
and for the case of analysis, an “impeller zone” of 5 times
the impeller volume, i.e., 4 m3, was assumed for includ-
ing the surroundings of the impeller discharge. The pulp
volumetric flowrate circulating through the impeller zone
was 6572 m3/h and the air volumetric flowrate entering
the impeller was around 1000 m3/h (Yianatos et al., 2008).
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
Measured time
Figure 1. Calculated versus measured data for effective pulp volumes of 85% and 88%, in 300 m3
and 160 m3 cells, respectively
Calculated
time,
min
Estimation of the Effective Collection Residence Time
in a Mechanical Cell
The main opportunity for an efficient particle-bubble con-
tact occurs when pulp circulates through the impeller zone
(Arbiter, 2000). In general, previous studies agree that the
collection process (particle-bubble aggregate formation)
mainly occurs in a zone around the impeller in mechani-
cal cells (Savassi, 2005 Amini et al., 2016 Mesa, 2020).
Further, a quiescent zone normally exists below the pulp-
froth interface, which typically has a lower pulp density,
promoting gangue segregation due to lower energy dissipa-
tion for particles collection (Savassi, 2005 Boeree, 2014
Mesa, 2020). This condition is required because it allows for
building a distinctive pulp-froth interface in order to pre-
vent the flooding condition and fine particles entrainment
into the concentrate (Yianatos and Henríquez, 2007a).
According to the previous understanding, the following
section presents a first estimation of the collection residence
time based on industrial data (Yianatos et al., 2008). In this
case, the hydrodynamic characterization of a self-aerated
mechanical cell of 130 m3, allowed for the identification
of the residence time the pulp spend in the impeller zone.
For this purpose, measurement of the pulp and air flowrates
circulating through the impeller, allowed for the estimation
of the active collection time.
Number of Circulations Through the Impeller in a Self-
Aerated Mechanical Cell
The study on the mixing characteristics in a single self-aer-
ated flotation cell of 130 m3, with a mean pulp residence
time of 5.0 min, showed that the time for a complete pulp
circulation through the impeller was around 1.0 min and
on average, the number of pulp circulations through the
impeller was five. In this case, a Flotation Number NF
to account for the mean number of particle circulations
through the active collection zone (high probability of col-
lection) was defined (Yianatos et al., 2008). In addition,
measurements of gas holdup using the radioactive tracer
technique showed that the main gas holdup occurs in the
upper half of the cell, indicating that the active collection
zone is smaller than the total pulp volume (Yianatos et al.,
2010b).
Time of Pulp Circulation Through the Impeller Zone
The 130 m3 self-aerated cell has an impeller around 0.8 m3,
and for the case of analysis, an “impeller zone” of 5 times
the impeller volume, i.e., 4 m3, was assumed for includ-
ing the surroundings of the impeller discharge. The pulp
volumetric flowrate circulating through the impeller zone
was 6572 m3/h and the air volumetric flowrate entering
the impeller was around 1000 m3/h (Yianatos et al., 2008).
0
5
10
15
20
25
30
35
0 5 10 15 20 25 30 35
Measured time
Figure 1. Calculated versus measured data for effective pulp volumes of 85% and 88%, in 300 m3
and 160 m3 cells, respectively
Calculated
time,
min