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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. W.L. Oliveira‐Filho, UFOP D.R. Silva, SAMARCO F.E. Almeida, SAMARCO. Contents. Introduction Background Field experimental studies Analyses of experimental data C onclusion.

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W.L. Oliveira‐Filho, UFOP D.R. Silva, SAMARCO F.E. Almeida, SAMARCO

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  1. 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

  2. Contents • Introduction • Background • Field experimental studies • Analyses of experimental data • Conclusion

  3. Introduction Desiccation & Sub-aerialStudiesTimeline

  4. Background • Alternativedisposaltechniques for slimes • Types • sub-aerialdeposition • Thickened • Paste • filtered • Common aspects • Intermitent: cyclesofwaitinganddisposalperiods • Physical processes: sedimentation, consolidationanddesiccation

  5. Background • Desiccation • Importance • The most effective phenomena for rehabilitation work, optimizing storage, and reducing risks regarding containment structure failure • Triggeringmechanisms • Surfacedrying • Loweringthe GWT • Driving force andPhases • Suction • 1D shrinkage • 3D shrinkage (cracking) • Comprehensiveworks • Abu-Hejleh& Znidarcic (1995) and Yao et al.(2002) • Konrad & Ayad (1997) • Fujiyasu(1997)

  6. Background Main input relationships for analyses with CONDES (Yao et al. 2002)

  7. 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’sslimes • To investigate consolidation separately from desiccation using a field experiment • To focus on slimes desiccation because was lesser known and more challenging

  8. Field experimental studies • Site & operations • Location: inside the Germano tailings impoundment (SamarcoMineração 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 Germanoimpoundment • Water cover: 5 to 10 cm deep during the filling process and consolidation period to prevent early desiccation. • Surfacewaterremoval: for the desiccation part of the test.

  9. 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.

  10. Field experimental studies Overview of the testing site

  11. Analysesof experimental data Input data for analyses with CONDES

  12. Analysesof experimental data Progress of the deposit height (at day 84 starts desiccation)

  13. Analysesof experimental data Progress of volumetric water content (day 84 starts desiccation)

  14. Analysesof experimental data Progress of gravimetric water content (desiccation starts at day 84)

  15. Analysesof experimental data Progress of bulk densities (desiccation starts at day 84)

  16. Analysesof experimental data Progress in solids content (desiccation starts at day 84)

  17. Analysesof experimental data Progress of porepressure at base (desiccation starts at day 84)

  18. Analysesof experimental data Meteorological data during field experiments (desiccation starts at day 84)

  19. Analysesof experimental data Progress of evaporation with data from the weather station and Class A device

  20. Analysesof experimental data Progress of cracking (a) day 89, (b) day 92, (c) day 94

  21. 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.

  22. THANK YOU

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