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 CYCLONE CONTAINMENT DIKE SEDIMENT
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) ROCK-FILL - STARTER EMBANKMENT JIG DIKES UNDERFLOW DIKES OVERFLOW/UNDERFLOW 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 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 Compaction Void ratio Sample SG Clay (%) Silt (%) Sand (%) Gravel (%) w optimum (%) r max (g/cm³) e max e min Total tailings 3.717 4.4 60.9 34.7 0.0 - - - - AM-1 Underflow AM-2 Underflow 3.741 1.8 30.6 67.4 0.2 - - 1.01 0.71 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 - Permeability test summary Sample Relative compaction (%) Re-moulding conditions Degree of compaction (%) Moisture (%) rdry (g/cm³) Permeability (m/s) AM-1 Underflow 60 AM-2 Underflow 70 Overflow - - - 85 11.6 2.039 1.10e-06 11.7 2.038 1.40e-06 12.8 1.878 4.20e-08
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 0 26.5 AM-1 Underflow 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 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 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: wlugao@vogbr.com.br