08/07/2011

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EVALUATION OF THE NICKEL-CNDGENERATION POTENTIAL OF THE TIO MINE WASTE ROCKSBenoît Plante, Ph.D. IMWADir. Benzaazoua, Mostafa; Co-dir. Bussière, Bruno. Sept. 2010

Outline2

Background and objectives

Materials and research program

Results and discussionsKinetic testing

Sorption studies

Implications for CND prediction

Conclusions and perspectives

Background and objectives3

Contaminated neutral drainage (CND): drainage waters with near-neutral pH which contain metal concentrations above regulated limits;

CND production CND production: Sulfide oxidation Metal/acidity generation;

Sufficient neutralization neutral pH;

Metal concentrations above regulated limits.

Possible metals in CND: As, Ni, Zn, Mo, Sn, Pb...

Background and objectives4

Origin of the study: the Tio mine case (Rio Tinto):No CND predicted with lab tests;

Sporadic Ni-CND conditions observed over some of the waste rock piles at the mine site after a fewthe waste rock piles at the mine site after a few decades.

Objectives of the study: Improve knowledge of Ni-generating and

Ni-decreasing phenomena within CND-generating waste rock piles;

Improve CND prediction for mine waste, particularly for Ni.

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Sydney, NS

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Background and objectives

45 km NE of Havre-Saint-Pierre;

Operating since 1950;

World-class massive ilmenite ore.

IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA

08/07/2011

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NW pit

Léowaste rock pile

Petitpaswaste rock pile

Tio pit

Grindingplant

Puyjalonwaste rock pile

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The Tio pit

Background and objectives9

Hemo-ilmenite ore: Hematite: Fe2O3;

Ilmenite: FeTiO3.

Anorthositic gangue, mainly calcic plagioclase: Anorthositic gangue, mainly calcic plagioclase: Na0.4Ca0.6Al1.6Si2.4O8 ≈ labradorite .

Sulfide traces within the waste rocks: pyrite (FeS2) with Ni traces;

millerite (NiS).

Waste rocks may contain as high as 70% residual hemo-ilmenite ore.

Background and objectives10

Previous studies on Tio waste rocks:Humidity cells (Bussière et al., 2005):No contamination.

Sulfide and gangue separation:Sulfide and gangue separation:Geochemical behaviours in weathering cells:

Sulfides•Generate acid;•Generate Ni.

Gangue minerals•Neutralize acid;•Retain Ni;•Limited Ni retention potential.

Materials and research program

Materials and research program12

Samples reflect waste rock heterogeneity : Hemo-ilmenite content (between 20 and 60 %);

Weathering level (fresh WR and WR ≈25 years).

Various scales of geochemical behaviour prediction: Various scales of geochemical behaviour prediction: Laboratory (humidity cells, 2 kg; weathering cells, 70 g);

Field test pads (30 m3, ≈100 tons);

Waste rock pile (approx. 2 745 000 m3).

Batch and kinetic Ni sorption tests.

IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA

08/07/2011

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Materials and research program13

Weathering cells

Humidity cells

Field test pads

Puyjalon SWpile

Puyjalon SEpile

Kinetic testing

S d

Results and discussions

Sorption studies

Implications for CND prediction

Results and discussion15

Typical results: humidity cells (lab) vs field test padsfor fresh and weathered (≈ 25 ans) waste rocks: Ni level differences:

Humidity cells (lab) Field test padsFresh waste rock 10

0,001

0,01

0,1

1

10

0 200 400 600

Ni (

mg/

L)

time (days)

Fresh waste rockWeathered waste rockDetection limitDir 019

0,001

0,01

0,1

1

10

Ni (

mg/

L)

Dates (yy-mm-dd)

Differences in S concentrations (from sulfide oxidation);

Similar S production rates in fresh and weathered WR: Similar sulfide oxidation rates in fresh and weathered WR:

Results and discussions16

Humidity cells (lab) Field test pads

0,01

0,1

1

10

100

1000

0 200 400 600

S (m

g/L)

time (days)

Fresh waste rock

Weathered waste rock

Detection limit

0,01

0,1

1

10

100

1000

S (m

g/L)

Dates (yy-mm-dd)

Waste rock weathering over ≈25 years do not decrease sulfide oxidation rates in the Tio waste rocks;

Field observations predict CND production on weathered waste rocks (Ni>3mg/L), not on fresh waste rocks (Ni<0,1mg/L);

A S d Ni t ti hi h fi ld l t t

Results and discussions17

Aqueous S and Ni concentrations higher on field scale tests: Effect of the liquid/solid ratio, higher in lab tests, which dilutes lab-scale

concentrations.

Lab-scale humidity cell tests inappropriate for CND prediction on waste rock.

Ni sorption phenomena in waste rocks: Batch tests:

Fresh WR have greater sorption capacities than weathered WR

Results and discussions18

90%

100%

10

11

i l l h

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

0

1

2

3

4

5

6

7

8

9

10

0 1000 2000 3000 4000 5000

% so

rbed

Ni (

mg/

L)

time (minutes)

Ni level-FreshNi level-WeatheredNi sorbed-FreshNi sorbed-Weathered

IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA

08/07/2011

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Conclusions and perspectives The following conclusions arise from the research program:

The Tio mine WR generate Ni-CND after a few years (or decades);

Sorption phenomena control Ni levels in drainage waters;

Delay before CND generation at the Tio mine;

Humidity cells tests inappropriate for CND prediction

Conclusions and perspectives20

Humidity cells tests inappropriate for CND prediction.

Perspectives: Column tests (lab) for CND prediction;

liquid/solid ratio closer to field conditions than humidity cells;

Sorption phenomena evaluation;

Development of a sorption assessment test :

Sorption capacity vs metal generation capacity

Many thanks!21

Industrial Chair partners:

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IMWA 2010 Sydney, Nova Scotia | “Mine Water & Innovative Thinking”

© by Authors and IMWA