4
Reverse Flotation, Regrind and Magnetic Separation
Circuit Scavenger
To obtain high-grade concentrates and maximize the
amount of concentrate to be produced, avoiding iron losses
in the tailings, several tests were carried out and finally a
pyrite reverse flotation circuit was designed to eliminate
sulfur followed by reverse iron flotation to reject mainly
siliceous gangue. The froth is dewatered and reground to a
size of 90%-25 µm and reprocessed in a three-pass magnetic
scavenger stage at 800 Gauss. This final circuit manages to
produce two products with differentiated qualities with the
possibility of mixing them to achieve an average final qual-
ity of 67.6% of total Fe, 4.3% of SiO2 and an overall final
recovery of 29.2% and an overall Sat. Fe recovery of 95.3%.
The Blaine index of this combined concentrate was 1,220
cm3/gr.
During the study a representative sample of the rougher
flotation tailings (froth) was submitted to determine lib-
eration of the gangue in the sample. This information was
used to assist in the iron scavenging test work. The sample
contained “locked grains of silicate (dominantly quartz)
and finer grained magnetite. Many of the locked grains
are 20–25µm. The SiO2 grade may be reduced further by
LIMS scavenging or selective flotation.” These mineralogi-
cal studies were carried out by Dr. Rodney C. Johnson in
his laboratory (Figure 6).
PROCESSING STAGES AND SELECTION
OF TECHNOLOGIES
All the information collected from the studies carried out
plus information on the results of additional tests carried
out with suppliers of various technologies that used sub-
samples of intermediate products, served to size the required
amount of equipment and analyze the size of facilities and
Table 3. Intermediate circuit testing – Estimated mass
balance
Product
Wt
(%)
Total
Fe (%)
Sat
Mag
Fe (%)
SiO
2 (%)
300 um Screen U/S
(direct)
100.0 35.17 27.25 33.72
Intermediate LIMS
Feed (calc) 102.0 35.32 27.39 33.53
Con (calc) 69.8 46.77 40.04 23.83
Tail (direct) 32.3 10.73 1.01 54.55
Regrinding Mill (Rod
Mill)
Feed (calc) 69.8 46.77 40.04 23.83
Discharge (calc) 69.8 46.77 40.04 23.83
Int. Circuit Screen
(53)
Feed (calc) 69.8 46.77 40.04 23.83
Undersize (direct) 67.7 47.13 40.84 23.80
Oversize (direct) 2.0 42.86 34.35 24.11
Head (calc) 100.0 35.39 27.99 33.72
Table 4. Intermediate circuit testing – Lock-cycle product
Davis tube analyses
Product
Wt
(%)
Total
Fe (%)
Sat
Mag
Fe (%)
SiO2
(%)
300 um Screen U/S
DT Con
71.5 45.29 38.01 25.86
Int. LIMS Tails DT
Con
15.0 15.60 4.53 46.39
Int. Circuit Screen (53
um)
Undersize DT Con 64.5 66.85 61.81 4.85
Oversize DT Con 67.9 56.83 49.42 13.83
Table 5. Cleaner flowsheet metallurgical comparison
Flowsheet
Concentrate
Grade
SiO2 (%)
Recovery
Sat Mag Fe (%)
Elutriation -Only* 5.5 98.1
LIMS-Only 6.9 99.0
Elut+LIMS 5.6 98.8
*Interpolated value from the test data.
Figure 5. Cleaner circuit testing – Comparison of
concentrate grade vs concentrate recovery The cleaner LIMS
concentrate chemical composition was found to be 66.7%
total Fe, 61.6% Satmagan magnetic Fe, 5.4% SiO
2 ,0.010%
Cu, and 0.070% S
Reverse Flotation, Regrind and Magnetic Separation
Circuit Scavenger
To obtain high-grade concentrates and maximize the
amount of concentrate to be produced, avoiding iron losses
in the tailings, several tests were carried out and finally a
pyrite reverse flotation circuit was designed to eliminate
sulfur followed by reverse iron flotation to reject mainly
siliceous gangue. The froth is dewatered and reground to a
size of 90%-25 µm and reprocessed in a three-pass magnetic
scavenger stage at 800 Gauss. This final circuit manages to
produce two products with differentiated qualities with the
possibility of mixing them to achieve an average final qual-
ity of 67.6% of total Fe, 4.3% of SiO2 and an overall final
recovery of 29.2% and an overall Sat. Fe recovery of 95.3%.
The Blaine index of this combined concentrate was 1,220
cm3/gr.
During the study a representative sample of the rougher
flotation tailings (froth) was submitted to determine lib-
eration of the gangue in the sample. This information was
used to assist in the iron scavenging test work. The sample
contained “locked grains of silicate (dominantly quartz)
and finer grained magnetite. Many of the locked grains
are 20–25µm. The SiO2 grade may be reduced further by
LIMS scavenging or selective flotation.” These mineralogi-
cal studies were carried out by Dr. Rodney C. Johnson in
his laboratory (Figure 6).
PROCESSING STAGES AND SELECTION
OF TECHNOLOGIES
All the information collected from the studies carried out
plus information on the results of additional tests carried
out with suppliers of various technologies that used sub-
samples of intermediate products, served to size the required
amount of equipment and analyze the size of facilities and
Table 3. Intermediate circuit testing – Estimated mass
balance
Product
Wt
(%)
Total
Fe (%)
Sat
Mag
Fe (%)
SiO
2 (%)
300 um Screen U/S
(direct)
100.0 35.17 27.25 33.72
Intermediate LIMS
Feed (calc) 102.0 35.32 27.39 33.53
Con (calc) 69.8 46.77 40.04 23.83
Tail (direct) 32.3 10.73 1.01 54.55
Regrinding Mill (Rod
Mill)
Feed (calc) 69.8 46.77 40.04 23.83
Discharge (calc) 69.8 46.77 40.04 23.83
Int. Circuit Screen
(53)
Feed (calc) 69.8 46.77 40.04 23.83
Undersize (direct) 67.7 47.13 40.84 23.80
Oversize (direct) 2.0 42.86 34.35 24.11
Head (calc) 100.0 35.39 27.99 33.72
Table 4. Intermediate circuit testing – Lock-cycle product
Davis tube analyses
Product
Wt
(%)
Total
Fe (%)
Sat
Mag
Fe (%)
SiO2
(%)
300 um Screen U/S
DT Con
71.5 45.29 38.01 25.86
Int. LIMS Tails DT
Con
15.0 15.60 4.53 46.39
Int. Circuit Screen (53
um)
Undersize DT Con 64.5 66.85 61.81 4.85
Oversize DT Con 67.9 56.83 49.42 13.83
Table 5. Cleaner flowsheet metallurgical comparison
Flowsheet
Concentrate
Grade
SiO2 (%)
Recovery
Sat Mag Fe (%)
Elutriation -Only* 5.5 98.1
LIMS-Only 6.9 99.0
Elut+LIMS 5.6 98.8
*Interpolated value from the test data.
Figure 5. Cleaner circuit testing – Comparison of
concentrate grade vs concentrate recovery The cleaner LIMS
concentrate chemical composition was found to be 66.7%
total Fe, 61.6% Satmagan magnetic Fe, 5.4% SiO
2 ,0.010%
Cu, and 0.070% S