w. lugão - vogbr, brazil m. almeida - vogbr, brazil a. guimarães - vogbr, brazil f. magalhães -...
TRANSCRIPT
W. Lugão - VOGBR, Brazil
M. Almeida - VOGBR, Brazil
A. Guimarães - VOGBR, Brazil
F. Magalhães - VOGBR, Brazil
S. Mohallem - ARCELORMITTAL, Brazil
Dry Stacking of Cycloned Tailings
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.
Introduction
IMAGE: 09-14-2007 – GOOGLE EARTH
TAILINGS DAM
SERRA AZUL MINE
SINTER FEED
TAILINGS DAM
SERRA AZUL MINE
DRY STACKING TAILINGS
IMAGE: 07-30-2011 – GOOGLE EARTH
Design Concept
DRY STACKING
DRYING PONDS- OVERFLOW TAILINGS
CONTAINMENT DIKE SEDIMENT
CYCLONE
ADesign Concept
WASTE PILE
DRY STACKING
WASTE/TAILINGS CO-DISPOSAL
INTERNAL DRAINAGE
DRAIN - SECTION
JIG TAILINGS
ROCK-FILL STARTER EMBANKMENT
Design Concept
Example: Plant level 1,030 m – tailings/waste co-disposal
A
WASTE PILE
UNDERFLOW TAILINGS
OVERFLOW / UNDERFLOW
TAILINGSJIG TAILINGS
ROCK-FILL STARTER EMBANKMENT
SECTION A
Design Concept
TAILINGS CELLS
100m25m
8m
Schematic profile (section A)
WASTE PILE
ROCK-FILL - STARTER EMBANKMENT
JIG DIKES
UNDERFLOW DIKES
OVERFLOW/UNDERFLOW
Design Concept
UNDERFLOW DIKES
Conception:Overflow – drainage in top and base!!!
Conception:Underflow dikes – vertical drainage!!!
Design Concept
Pilot Tests – Total Tailings
Pilot Tests - Cyclone
UNDERFLOW TAILINGS
CYCLONE
Tailings characterisation
Perc
ent fi
ner t
han
Grain size - millimeters
Jig Tailings
Total Tailings
AM01 Underflow
AM02 Underflow
Overflow
Sample
Re-moulding conditionsPermeability
(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
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 0.2 - - 1.09 0.77
Overflow 3.405 7.2 77.2 15.6 0.0 13.0 2.208 - -
Jig 3.544 0.2 5.0 65.5 29.3 - - - -
Table - Test results
Table - Permeability test summary
SampleEffective strength parameters 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
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
Table 6 Parameters for materials used in stress-strain and stability analyses
Table - Triaxial test results
Table - Parameters for materials used in stress-strain and stability analyses
MATERIALS
FINITE ELEMENT MODEL (SIGMA)
FINAL STACK CONDITION
Stress-strain analysis
The safety factor for the critical failure surface is 1.97 and is therefore satisfactory.
Stability Analyses
Stability analysis results for waste rock/tailings co-disposal – Global – Non-Circular failure.
OVERFLOW TAILINGS – DISPOSAL SEQUENCE
Operation
Building the tailings cells
ROCK-FILL - STARTER
EMBANKMENT
DRYING PONDS
UNDERFLOWLEVEL 1000.5 m
OVERFLOWLEVEL 1000 m
CONTAINMENT DIKE
Situation - December 2012
•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.
Final Remarks
