Dry Stacking of Cycloned Tailings
W. Lugão - VOGBR, Brazil
M. Almeida - VOGBR, Brazil
A. Guimarães - VOGBR, Brazil
F. Magalhães - VOGBR, Brazil
S. Mohallem - ARCELORMITTAL, Brazil
Introduction
Tailings at ArcelorMittal Mineração’s Serra Azul Mine are currently disposed of in a
tailings dam, which is at the end of its useful life. Another tailings disposal facility is
required and there is no place for another conventional dam.
A drained stacking scheme was proposed, with the following advantages over
conventional dams:
- It allows tailings to be stored in stacks, which poses less risk as it does not involve
the storage of water;
- It will be located in an area that was occupied by a fines stockpile (sinter feed),
which is why no additional land will have to be purchased;
- It allows mining operations to proceed without interruption.
IMAGE: 09-14-2007 – GOOGLE EARTH
SERRA AZUL MINE
TAILINGS DAM
SINTER FEED
IMAGE: 07-30-2011 – GOOGLE EARTH
SERRA AZUL MINE
TAILINGS DAM
DRY STACKING
TAILINGS
Design Concept
DRY STACKING
DRYING PONDSOVERFLOW TAILINGS
CONTAINMENT DIKE SEDIMENT
CYCLONE
Design Concept
A
WASTE/TAILINGS CO-DISPOSAL
WASTE PILE
DRY STACKING
Design Concept
INTERNAL DRAINAGE
DRAIN - SECTION
JIG TAILINGS
ROCK-FILL STARTER
EMBANKMENT
Design Concept
A
Example: Plant level 1,030 m – tailings/waste co-disposal
SECTION A
WASTE PILE
UNDERFLOW
TAILINGS
JIG TAILINGS
OVERFLOW /
UNDERFLOW
TAILINGS
8m
25m
100m
ROCK-FILL STARTER
EMBANKMENT
TAILINGS CELLS
Design Concept
Schematic profile (section A)
OVERFLOW/UNDERFLOW
UNDERFLOW DIKES
ROCK-FILL
STARTER
EMBANKMENT
JIG DIKES
WASTE PILE
Design Concept
UNDERFLOW DIKES
Conception:
Underflow dikes – vertical drainage!!!
Conception:
Overflow – drainage in top and base!!!
Pilot Tests – Total Tailings
Pilot Tests - Cyclone
UNDERFLOW TAILINGS
CYCLONE
Percent finer than
Tailings characterisation
Jig Tailings
Total Tailings
AM01
Underflow
AM02
Underflow
Overflow
Grain size - millimeters
Table -
Test results
Full gradation
Table -
Sample
SG
Total tailings
Compaction
woptimum
rmax
(g/cm³)
(%)
Void ratio
emax
emin
-
-
-
-
-
1.01
0.71
0.2
-
-
1.09
0.77
15.6
0.0
13.0
2.208
-
-
65.5
29.3
-
-
-
-
Clay (%)
Silt (%)
Sand (%)
Gravel (%)
3.717
4.4
60.9
34.7
0.0
-
AM-1
Underflow
3.741
1.8
30.6
67.4
0.2
AM-2
Underflow
3.838
1.4
33.6
64.7
Overflow
3.405
7.2
77.2
Jig
3.544
0.2
5.0
Permeability test summary
Re-moulding conditions
Sample
Relative
compaction (%)
Degree of
compaction (%)
Permeability
(m/s)
Moisture (%)
rdry
(g/cm³)
11.6
2.039
1.10e-06
11.7
2.038
1.40e-06
12.8
1.878
4.20e-08
AM-1 Underflow
60
AM-2 Underflow
70
Overflow
-
85
Table 6
Parameters for materials used in stress-strain and stability analyses
Table -
Triaxial test results
Effective strength parameters
Sample
Table -
Total strength parameters
c’ (kPa)
f’ (°)
c (kPa)
f (°)
AM-1 Underflow
3.89
29.7
0
26.5
AM-1 Underflow
5.00
31.2
17.20
18.7
Overflow
4.05
30.1
5.20
11.6
Parameters for materials used in stress-strain and stability analyses
Material
Density (kN/
m³)
c’ (kPa)
f’ (°)
Deformation
modulus (MPa)
n (Poisson’s
ratio)
Foundation
17.0
15
28
20,000
0.20
Rock-fill
23.0
0
42
80
0.25
Underflow
22.8
0
30
20
0.30
Overflow
20.0
2
26
4.0
0.40
Jigue
23.0
0
36
27.5
0.25
Waste
22.0
0
34
40
0.33
Stress-strain analysis
MATERIALS
FINITE ELEMENT MODEL
(SIGMA)
FINAL STACK CONDITION
Stability Analyses
The safety factor for the critical failure surface is 1.97 and is therefore satisfactory.
Stability analysis results for waste rock/tailings co-disposal – Global – Non-Circular failure.
Operation
OVERFLOW TAILINGS – DISPOSAL SEQUENCE
Building the tailings cells
Situation - December 2012
DRYING
PONDS
ROCK-FILL STARTER
EMBANKMENT
CONTAINMENT DIKE
UNDERFLOW
LEVEL 1000.5 m
OVERFLOW
LEVEL 1000 m
Final Remarks
•Stability analyses have arrived at a satisfactory safety factor, assuming the long-term
(drained) final stack condition; the maximum predicted subsidence in dry stacks will
be acceptable even in the most critical long-term condition;
•It is suggested that the cyclone system operating techniques should be reviewed, as
the system is now working with overflow rates in excess of design rates. As a result,
underflow requirements are being filled with jig tailings currently available at the
mine for such purpose.
•It is also recommended that alternative methods should be developed for carrying
overflow tailings from dewatering ponds to the storage basins, including alternative
deposition methods, with a view to improving the process which is currently
undertaken using trucks.
• An investigation campaign is programmed, composed of SPT, CPTU, Vane,
permeability and laboratory tests;
• ArcelorMittal will continue monitoring the performance of the system.
Thank you!
Contact:
wlugao@vogbr.com.br