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

Contact:

wlugao@vogbr.com.br

Thank you!