1. 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

2. 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.

3. IMAGE: 09-14-2007 – GOOGLE EARTH
SERRA AZUL MINE
TAILINGS DAM
SINTER FEED

4. IMAGE: 07-30-2011 – GOOGLE EARTH
SERRA AZUL MINE
TAILINGS DAM
DRY STACKING TAILINGS

5. CONTAINMENT DIKE SEDIMENT
Design Concept
DRY STACKING
DRYING PONDS- OVERFLOW TAILINGS
CONTAINMENT DIKE SEDIMENT
CYCLONE

6. WASTE/TAILINGS CO-DISPOSAL
Design Concept A
WASTE/TAILINGS CO-DISPOSAL
WASTE PILE
DRY STACKING

7. ROCK-FILL STARTER EMBANKMENT
Design Concept
Internal drainage
DRAIN - SECTION
JIG TAILINGS
ROCK-FILL STARTER EMBANKMENT

8. Example: Plant level 1,030 m – tailings/waste co-disposal
Design Concept
Example: Plant level 1,030 m – tailings/waste co-disposal A
WASTE PILE
UNDERFLOW TAILINGS
OVERFLOW / UNDERFLOW TAILINGS
JIG TAILINGS
ROCK-FILL STARTER EMBANKMENT
SECTION A
TAILINGS CELLS
100m
25m 8m

9. Schematic profile (section A)
Design Concept
Schematic profile (section A)
OVERFLOW/UNDERFLOW
UNDERFLOW DIKES
WASTE PILE
JIG DIKES
ROCK-FILL - STARTER EMBANKMENT

10. Design Concept Conception: Underflow dikes – vertical drainage!!!
Overflow – drainage in top and base!!!

11. Pilot Tests – Total Tailings

12. Pilot Tests - Cyclone
UNDERFLOW TAILINGS
CYCLONE

13. Tailings characterisation
Percent finer than
Grain size - millimeters
Jig Tailings
Total Tailings
AM01 Underflow
AM02 Underflow
Overflow

14. Table - Permeability test summary
Table - Test results
Sample SG
Full gradation
Compaction
Void ratio
Clay (%)
Silt (%)
Sand (%)
Gravel (%)
woptimum
(%)
rmax (g/cm³)
emax
emin
Total tailings
3.717
4.4
60.9
34.7
0.0 -
AM-1 Underflow
3.741
1.8
30.6
67.4
0.2
1.01
0.71
AM-2 Underflow
3.838
1.4
33.6
64.7
1.09
0.77
Overflow
3.405
7.2
77.2
15.6
13.0
2.208
Jig
3.544
5.0
65.5
29.3
Table - Permeability test summary
Sample
Re-moulding conditions
Permeability (m/s)
Relative compaction (%)
Degree of compaction (%)
Moisture (%)
rdry (g/cm³)
AM-1 Underflow 60 -
11.6
2.039
1.10e-06
AM-2 Underflow 70
11.7
2.038
1.40e-06
Overflow 85
12.8
1.878
4.20e-08

15. Table - Triaxial test results
Table 6 Parameters for materials used in stress-strain and stability analyses
Table - Triaxial test results
Sample
Effective strength parameters
Total strength parameters
c’ (kPa)
f’ (°)
c (kPa)
f (°)
AM-1 Underflow
3.89 
29.7
26.5
5.00 
31.2
17.20 
18.7
Overflow
4.05
30.1
5.20
11.6 
Table - 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 42 80
0.25
Underflow
22.8 30 20
0.30
Overflow
20.0 2 26
4.0
0.40
Jigue 36
27.5
Waste
22.0 34 40
0.33

16. Stress-strain analysis
MATERIALS
FINITE ELEMENT MODEL (SIGMA)
FINAL STACK CONDITION

17. 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.

18. Operation
OVERFLOW TAILINGS – DISPOSAL SEQUENCE

19. Building the tailings cells

20. ROCK-FILL - STARTER EMBANKMENT
Situation - December 2012
DRYING PONDS
ROCK-FILL - STARTER EMBANKMENT
UNDERFLOW
LEVEL m
CONTAINMENT DIKE
OVERFLOW
LEVEL 1000 m

21. 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.

22. Contact: wlugao@vogbr.com.br
Thank you!
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