Transcript Dry Stacking of Cycloned Tailings.
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 PONDS OVERFLOW TAILINGS CONTAINMENT DIKE SEDIMENT CYCLONE
WASTE PILE
Design Concept
A
WASTE/TAILINGS CO-DISPOSAL DRY STACKING
INTERNAL DRAINAGE
Design Concept
ROCK-FILL STARTER EMBANKMENT JIG TAILINGS DRAIN - SECTION
Design Concept
A
Example: Plant level 1,030 m – tailings/waste co-disposal
SECTION A WASTE PILE UNDERFLOW TAILINGS JIG TAILINGS ROCK-FILL STARTER EMBANKMENT OVERFLOW / UNDERFLOW TAILINGS
8m 25m 100m
TAILINGS CELLS
Schematic profile (section A)
Design Concept
ROCK-FILL STARTER EMBANKMENT JIG DIKES OVERFLOW/UNDERFLOW UNDERFLOW DIKES WASTE PILE
Design Concept
Conception: Underflow dikes – vertical drainage!!!
UNDERFLOW DIKES
Conception: Overflow – drainage in top and base!!!
Pilot Tests – Total Tailings
Pilot Tests - Cyclone
CYCLONE UNDERFLOW TAILINGS
Tailings characterisation
Grain size - millimeters
Jig Tailings Total Tailings AM01 Underflow AM02 Underflow Overflow
Table Test results
Sample SG
Total tailings AM-1 Underflow AM-2 Underflow Overflow Jig 3.717
3.741
3.838
3.405
3.544
Clay (%)
4.4
1.8
1.4
7.2
0.2
Full gradation Silt (%)
60.9
30.6
Sand (%)
34.7
67.4
Gravel (%) w Compaction optimum (%)
r
max (g/cm³) Void ratio e max e min
0.0
0.2
1.01
0.71
33.6
77.2
5.0
64.7
15.6
65.5
0.2
0.0
29.3
13.0
2.208
1.09
0.77
Table Permeability test summary
Re-moulding conditions Sample Relative compaction (%) Degree of compaction (%)
-
Moisture (%)
AM-1 Underflow 60 11.6
AM-2 Underflow 70 11.7
85 Overflow 12.8
r
dry (g/cm³)
2.039
2.038
1.878
Permeability (m/s)
1.10e-06 1.40e-06 4.20e-08
Table 6 Parameters for materials used in stress-strain and stability analyses Table Triaxial test results
Effective strength parameters Sample c’ (kPa)
f
’ ( ° )
AM-1 Underflow 3.89
29.7
AM-1 Underflow Overflow 5.00
4.05
31.2
30.1
Total strength parameters c (kPa)
f
( ° )
0 26.5
17.20
5.20
18.7
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 Rock-fill Underflow Overflow Jigue Waste 17.0
23.0
22.8
20.0
23.0
22.0
15 0 0 2 0 0 28 42 30 26 36 34 20,000 80 20 4.0
27.5
40 0.20
0.25
0.30
0.40
0.25
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
ROCK-FILL STARTER EMBANKMENT CONTAINMENT DIKE UNDERFLOW LEVEL 1000.5 m DRYING PONDS 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: [email protected]