Thickening of iron ore tailings slimes using sub-aerial

Report
Thickening of iron ore tailings
slimes using sub-aerial deposition:
field experimental observations
W.L. Oliveira‐Filho, UFOP
D.R. Silva, SAMARCO
F.E. Almeida, SAMARCO
Contents
• Introduction
• Background
• Field experimental studies
• Analyses of experimental data
• Conclusion
Introduction
Desiccation & Sub-aerial Studies Timeline
Background
Alternative 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
Background
Desiccation
• 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)
Background
Main input relationships for analyses with CONDES (Yao et al. 2002)
Compressibility
Constitutive
relations
Cracking function
a - function
Permeability
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
Field experimental studies
Site & 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.
Field experimental studies
Instrumentation, 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.
Field experimental studies
Overview of the testing site
Analyses of experimental data
Input data for analyses with CONDES
Analyses
Data/Parameters
A (kPa-1)
2.5438
B
C (m/dia)
D
Z (kPa)
Bottom
Top
A
B
C
D
-0.1920
9.45 x 10-4
4.2370
0.0495
hp= variable
Surcharge null
3.89
0.0603
34
0.3859
0.0508
1.3665
0.626 x 1018
Bottom
Top
hp= -0.55 m
Evap. rate =
Compressibility and Permeability parameters
Consolidation
Boundary conditions
Specific gravity - G
Filling rate (m/day)
Filling period (day)
Cracking function parameters
Desiccation
Boundary conditions
0.002 m/day
Analyses of experimental data
Progress of the deposit height (at day 84 starts desiccation)
Analyses of experimental data
Progress of volumetric water content (day 84 starts desiccation)
Analyses of experimental data
Progress of gravimetric water content (desiccation starts at day 84)
Analyses of experimental data
Progress of bulk densities (desiccation starts at day 84)
Analyses of experimental data
Progress in solids content (desiccation starts at day 84)
Analyses of experimental data
Progress of porepressure at base (desiccation starts at day 84)
Analyses of experimental data
Meteorological data during field experiments (desiccation starts at day 84)
Analyses of experimental data
Progress of evaporation with data from the weather station and Class A device
Analyses of experimental data
Progress of cracking (a) day 89, (b) day 92, (c) day 94
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.
THANK YOU

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