w.l. oliveira‐filho, ufop d.r. silva, samarco f.e. almeida, samarco thickening of iron ore...
TRANSCRIPT
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W.L. Oliveira Filho, UFOP‐
D.R. Silva, SAMARCO
F.E. Almeida, SAMARCO
Thickening of iron ore tailings slimes using sub-aerial deposition: field experimental observations
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• Introduction
• Background
• Field experimental studies
• Analyses of experimental data
• Conclusion
Contents
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Introduction
Desiccation & Sub-aerial Studies Timeline
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BackgroundAlternative disposal techniques for slimes
• Types• sub-aerial deposition• Thickened• Paste• filtered
• Common aspects• Intermitent: cycles of waiting and disposal periods• Physical processes: sedimentation, consolidation and desiccation
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BackgroundDesiccation
• Importance • The most effective phenomena for rehabilitation work, optimizing storage, and
reducing risks regarding containment structure failure
• Triggering mechanisms• Surface drying• Lowering the GWT
• Driving force and Phases• Suction• 1D shrinkage• 3D shrinkage (cracking)
• Comprehensive works• Abu-Hejleh & Znidarcic (1995) and Yao et al. (2002)• Konrad & Ayad (1997) • Fujiyasu (1997)
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Background
Constitutiverelations
Compressibility
Permeability
Cracking function
a - function
Main input relationships for analyses with CONDES (Yao et al. 2002)
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Field experimental studies
Goal & strategies
• To gain some understanding of the main mechanisms that play a role in the sub-aerial method applied to Samarco’s slimes
• To investigate consolidation separately from desiccation using a field experiment
• To focus on slimes desiccation because was lesser known and more challenging
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Field experimental studiesSite & operations• Location: inside the Germano tailings impoundment (Samarco Mineração S.A.) in
Mariana, MG.
• Impoundment figures: 3 m high ring dyke, confining an area of 4,850 m2.
• Foundation: 2 m of coarse siliceous tailings, grading from fine sand to medium silt, underlain by a deep layer of iron tailings slimes.
• Ground water table: at the contact of those layers, 2 m below the surface.
• Drainage system: stop logs installed at the lower part (bottom at 2% slope)
• Access: a pier to the centre of the testing area for instrumentation maintenance and sampling operations
• Filling: slimes pumped from an adjacent slimes pond at the Germano impoundment
• Water cover: 5 to 10 cm deep during the filling process and consolidation period to prevent early desiccation.
• Surface water removal: for the desiccation part of the test.
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Field experimental studiesInstrumentation, testing & instalation
• Devices: • Geotechnical: Thermistors, settlement devices (staff gauges), tensiometers,
piezometers, time domain reflectometry probes (TDRs)• Climate: Weather station and a class A pan test
• Placement: • Thermistors and TDR probes launched at certain pond elevations during the deposit
filling (movable position)• All other instruments at fixed positions
• Testing• Periodic sampling using a stationary sampler• Gravimetric water content determination• Specific gravity and bulk density.
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Field experimental studies
Overview of the testing site
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Analyses of experimental data
Analyses Data/Parameters
Consolidation
Compressibility and Permeability parameters
A (kPa-1) 2.5438
B -0.1920C (m/dia) 9.45 x 10-4
D 4.2370Z (kPa) 0.0495
Boundary conditions Bottom hp= variable
Top Surcharge nullSpecific gravity - G 3.89Filling rate (m/day) 0.0603Filling period (day) 34
Desiccation
Cracking function parameters
A 0.3859B 0.0508C 1.3665D 0.626 x 1018
Boundary conditions
Bottom hp= -0.55 mTop Evap. rate =
0.002 m/day
Input data for analyses with CONDES
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Analyses of experimental data
Progress of the deposit height (at day 84 starts desiccation)
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Analyses of experimental data
Progress of volumetric water content (day 84 starts desiccation)
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Analyses of experimental data
Progress of gravimetric water content (desiccation starts at day 84)
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Analyses of experimental data
Progress of bulk densities (desiccation starts at day 84)
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Analyses of experimental data
Progress in solids content (desiccation starts at day 84)
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Analyses of experimental data
Progress of porepressure at base (desiccation starts at day 84)
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Analyses of experimental data
Meteorological data during field experiments (desiccation starts at day 84)
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Analyses of experimental data
Progress of evaporation with data from the weather station and Class A device
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Analyses of experimental data
Progress of cracking (a) day 89, (b) day 92, (c) day 94
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Conclusions• Characterization of the desiccation behaviour of a fine tailings from the
iron ore milling operations was successfully reached.
• A test section was built and monitored, using an extensive sort of instruments and tests.
• Material behaviour and boundary conditions were assessed such as settlement, water content, bulk densities, solids content, porewater pressures, evaporation rates, etc.
• Cracking morphology has also been described.
• Sub-aerial deposition conditions was examined as a part a large study of alternative methods for slimes.
• A brief comparison of field data with a numerical modelling of the problem was presented and the results have shown consistent agreement.
• Overall, the research seems to suggest that reasonable efficiency with slimes thickening can be achieved by the sub-aerial disposition method.
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THANK YOU