3
A Denver, D12 laboratory flotation machine employed
for benchtop flotation tests, while 3-inch (75 mm) diameter
Eriez laboratory-scale flotation columns was used in batch-
continuous operation to investigate the column flotation
response. During benchtop flotation tests, the pH level was
adjusted to approximately 9.5 using a 10% NaOH solu-
tion in rougher direct flotation conditioning. The feed was
conditioned at 50–65% solids for 2 minutes with sodium
silicate, 1 minute with starch, and finally 2 minutes with
collector.
Figure 2 schematically shows the Eriez laboratory scale
flotation column. Eriez laboratory columns utilize an Eriez
CavTube sparging system, which consists of an in-line sparg-
ing device that works in conjunction with a recycle pump.
The pump withdraws pulp from the base of the column and
distributes it through the sparger. Air is added to the pulp
prior to the sparger and then injected back into the column
flotation cell. The high shear and cavitation induced into
the liquid flow as it passes through the CavTube creates a
fine bubble dispersion for particle collection and is espe-
cially effective for treatment of fine material. The column
cell test assembly is fully automated. During completion of
each test, the froth level was maintained through the use
of a PID loop controller, in conjunction with a pressure
transducer and an electronic peristaltic underflow pump.
Manual air and wash water flow meters were also present
for control of those operating parameters. A polyglycol
frother was injected into the column cell through the use of
a peristaltic chemical metering pump.
The column feed was prepared by transferring a
weighed amount of solid material into a 20-gallon agitated
feed slurry tank, followed by the addition of tap water to
attain the desired percent solids and adjustment of pH
level to approximately 9.5 using a 10% NaOH solution.
The feed slurry and sodium silicate depressant solution
were continuously pumped into the sodium silicate condi-
tioning tank for 2 minutes of conditioning. After sodium
silicate conditioning, the feed slurry was pumped to the
starch conditioning tank for 1 minute of further condition-
ing. The depressant conditioned feed slurry and apatite
collector were then pumped into the final collector con-
ditioning tank. Finally, the collector conditioned feed was
pumped to a rougher column cell using a peristaltic pump.
The conditioning time within each conditioning stage was
Table 1. Variables for three-factor three-level design
Factors and Values
A B C
Levels Washwater Feed P80 Feed Solids
(Liter/Minute) (Micron) (%)
Low -1 0 20 10
Middle 0 400 38 17.5
High 1 800 53 25
Table 2. Three-factor three-level central composite design
Test Factors and Levels
A B C
Std Run Washwater Feed P80 Feed Solids
13 1 0 0 0
3 2 -1 1 0
9 3 0 -1 -1
16 4 0 0 0
10 5 0 1 -1
15 6 0 0 0
8 7 1 0 1
17 8 0 0 0
4 9 1 1 0
7 10 -1 0 1
12 11 0 1 1
6 12 1 0 -1
1 13 -1 -1 0
14 14 0 0 0
5 15 -1 0 -1
11 16 0 -1 1
2 17 1 -1 0
Figure 2. Schematic of Eriez lab flotation column
A Denver, D12 laboratory flotation machine employed
for benchtop flotation tests, while 3-inch (75 mm) diameter
Eriez laboratory-scale flotation columns was used in batch-
continuous operation to investigate the column flotation
response. During benchtop flotation tests, the pH level was
adjusted to approximately 9.5 using a 10% NaOH solu-
tion in rougher direct flotation conditioning. The feed was
conditioned at 50–65% solids for 2 minutes with sodium
silicate, 1 minute with starch, and finally 2 minutes with
collector.
Figure 2 schematically shows the Eriez laboratory scale
flotation column. Eriez laboratory columns utilize an Eriez
CavTube sparging system, which consists of an in-line sparg-
ing device that works in conjunction with a recycle pump.
The pump withdraws pulp from the base of the column and
distributes it through the sparger. Air is added to the pulp
prior to the sparger and then injected back into the column
flotation cell. The high shear and cavitation induced into
the liquid flow as it passes through the CavTube creates a
fine bubble dispersion for particle collection and is espe-
cially effective for treatment of fine material. The column
cell test assembly is fully automated. During completion of
each test, the froth level was maintained through the use
of a PID loop controller, in conjunction with a pressure
transducer and an electronic peristaltic underflow pump.
Manual air and wash water flow meters were also present
for control of those operating parameters. A polyglycol
frother was injected into the column cell through the use of
a peristaltic chemical metering pump.
The column feed was prepared by transferring a
weighed amount of solid material into a 20-gallon agitated
feed slurry tank, followed by the addition of tap water to
attain the desired percent solids and adjustment of pH
level to approximately 9.5 using a 10% NaOH solution.
The feed slurry and sodium silicate depressant solution
were continuously pumped into the sodium silicate condi-
tioning tank for 2 minutes of conditioning. After sodium
silicate conditioning, the feed slurry was pumped to the
starch conditioning tank for 1 minute of further condition-
ing. The depressant conditioned feed slurry and apatite
collector were then pumped into the final collector con-
ditioning tank. Finally, the collector conditioned feed was
pumped to a rougher column cell using a peristaltic pump.
The conditioning time within each conditioning stage was
Table 1. Variables for three-factor three-level design
Factors and Values
A B C
Levels Washwater Feed P80 Feed Solids
(Liter/Minute) (Micron) (%)
Low -1 0 20 10
Middle 0 400 38 17.5
High 1 800 53 25
Table 2. Three-factor three-level central composite design
Test Factors and Levels
A B C
Std Run Washwater Feed P80 Feed Solids
13 1 0 0 0
3 2 -1 1 0
9 3 0 -1 -1
16 4 0 0 0
10 5 0 1 -1
15 6 0 0 0
8 7 1 0 1
17 8 0 0 0
4 9 1 1 0
7 10 -1 0 1
12 11 0 1 1
6 12 1 0 -1
1 13 -1 -1 0
14 14 0 0 0
5 15 -1 0 -1
11 16 0 -1 1
2 17 1 -1 0
Figure 2. Schematic of Eriez lab flotation column