controls of toxic elements in abiotic reductive dissolution of uranium mill raffinates and tailings...

CONTROLS OF TOXIC ELEMENTS IN ABIOTIC REDUCTIVE DISSOLUTION OF URANIUM MILL RAFFINATES AND TAILINGS UNDER ALKALINE

CONDITIONS

Mario Alberto Gomez, Jim Hendry, Joseph Essilfie-Dughan, Jian Chen and Samir

Elouatik

Geological Society of America Annual MeetingSession 190: Trace Elements and Organics in Environmental and Urban

Geochemistry IIOctober 21, 2014

Vancouver, Canada

1. Introduction and Motivation

2. Experimental Approach

3. Results and Discussion

4. Conclusions

Outline

2

• U-mill Tailings in Northern Saskatchewan, Canada are alkaline (pH 8 to 10) and often contain elevated concentrations of the elements of concern (EOC) As, Se, Mo and Ni.

• These EOCs are immobilized within the Tailings solid phase with Ferrihydrite (FH) via lime neutralization of acidic Raffinate solution to pH 8 to 10.

• Although the Tailings are oxic,concern exists as to the impact of anaerobic conditions on the immobilization of these EOCs in the long term.

Introduction and Motivation

3

• Research suggests FH and EOC-FH (EOC= As, Mo, Se or Ni) may be unstable under moderately reducing conditions, and may undergo phase/redox transformation which can release EOCs into the aqueous phase.

Hansel et al. Environ. Sci. Technol. 2005, 39, 7147-7153

4

Introduction and Motivation

Final Neutralized Deilmann and McArthur

Tailings (FNT)

Final Neutralized Raffinates (FNR)

EOC-Ferrihydrite (Synthetic)5

Experimental Approach to Understanding the Neutralized

Raffinates and Tailings

6

Previous Rabbit Lake in-pit Tailings EXAFS data

Moldovan et al. Environ. Sci. Technol. 2003, 37, 873-873

Rabbit Lake

Tailings

AsO4-Ferrihydrite

Characteristic

As-Fe bond

As-O

Scorodite

7

Previous Rabbit Lake in-pit Tailings EXAFS data

Moldovan et al. Environ. Sci. Technol. 2003, 37, 873-873

• As bonded only to Fe (i.e. ferrihydrite) via Bidentate bridging.

• Al and Mg were considered as amorpohous/crystalline hydro/oxide

phases

Ferrihydrite

(FH)

Mg-Al

Hydrotalcite

(HTLC)

8Gomez et al. Environ. Sci. Technol. 2013, 47, 7883-7891.



9

As K-edge EXAFS Data on the McArthur ore

Key Lake Final Neutralized Raffinate at pH 10 Sample

As-O

bond

Characteristic

As-Fe bond

Key Lake Final Neutralized Raffinate

at pH 10

AsO4 adsorbed Hydrotalcite

AsO4 adsorbed Ferrihydrite


Tailings (FNT)

Final Neutralized Raffinates (FNR)

EOC-FH

Mg-Al/Fe-SO4/CO

3 HTLC

EOC-MgAlFe

SO4CO

3 HTLC

10



Gomez et al. RSC Advances.

2013, 3, 25812-22.

11

Sample Origin: Key Lake’s Bulk Neutralization Process (KBNP)

Selected Key Lake Bulk Neutralization Process Samples

Gomez et al. Environ. Sci. Technol. 2013, 47, 7883-7891.

13


Key Lake Final Neutralized Raffinates (pH 10) and process step

samples at pH 4 and 6


at pH 10

Key Lake Bulk Neutralization

Process Sample at pH 6

Key Lake Bulk Neutralization

Process Sample at pH 4

Data collection and fitting done by

Dr. Jinru Lin

14


Key Lake Final Neutralized Raffinates at pH 10 and process

sample at pH 10


at pH 10

AsO4 adsorbed Hydrotalcite

Data collection and fitting done by

Dr. Jinru Lin

15

N2(g)

N2(g

)

Raman

XANES EXAFS

TEM



Reductive Dissolution of Synthetic Mg-Al/Fe-

SO4/CO3 Hydrotalcites

16

Surface

Bulk

17

McArthur Derived Raffinate

pH 8_10mM Fe(II)(aq) pH 10_0.5mM Fe(II)(aq)

McArthur and Deilmann Derived Tailings

Reductive Dissolution of Neutralized Raffinates and Tailings

Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 10 mM Fe(II)(aq))

18


19

• In both Mg-Al HTLC and FH phases, the EOCs (e.g. Ni and As)

remain in the solid phases after the 7 day and 6 month

reactions.

• Phase transformation of Neutralized Raffinates and Tailings to Green

Rust (stable up to 6 months or longer!).20


Fe L-edge Green Rust

Ferrihydrite

Tailings

Raffinate

21

As K-edge EXAFS Data of the Reductive Dissolution of FNR (pH 8 and 10 mM Fe(II)(aq))

Unreacted Key Lake Final

Neutralized Raffinate at pH 10

Reacted Key Lake Final Neutralized

Raffinate at pH 8 and 7 days


Raffinate at pH 8 and 6 months

AsO4 adsorbed Green rust (SO4)

Characteristic

As-Fe

22

Fe(III) Fe(II)

Fe(III) Mg(II) Fe(II)


• Green Rust formation from both Mg-Al HTLC and FH phases.

• Surface and bulk phase transformations observed.

Mg-Al HTLC FH

23

Amorphous

substrate

Another

distinct

particle=>

Occurring

throughout

sample


Magnetite Formation

24

Reductive Dissolution of Neutralized Raffinates and Tailings (pH 10 and 0.5 mM Fe(II)(aq))

25

Characteristic

As-Fe

As K-edge EXAFS Data of the Reductive Dissolution of FNR (pH 10 and 0.5 mM Fe(II)(aq))

Unreacted Key Lake Final

Neutralized Raffinate at pH 10


Raffinate at pH 10 and 6 months


Raffinate at pH 10 and 7 days

AsO4 adsorbed Green rust (SO4)

Global Conclusions

Under all conditions tested, none of the Neutralized Raffinates,

nor Tailings released any significant EOCs (≤ 0.1 w.t. %) after

7 days or 6 months.

No EOCs were released when Green Rust was favored @ pH

8 and 10mM Fe(II)(aq) for all samples tested.

The lack of EOC release occurred in spite of clear phase

transformations (e.g. Green Rust) and even FH/GR

crystallization to Magnetite.

The abiotic reduction behavior is combination of both individual

phases but also their common origin.26

Future Work, Acknowledgement and Thanks…..

• Future Work: As K-edge EXAFS modelling and manuscript write up.

• Sponsors: Cameco Corp and NSERC.

• Collaborators: H. Assaoudi (McGill), G. Ventruti(Università degli Studi di Bari) F. Nelson, J. Koshinsky, J Robertson, J. Fan, T. Bonli (U of S), S. Eluatik (U of M), Jian Chen (NINT), M. Celikin (INRS), SGM/SM (Jay Dynes, Tom Regier), and HXMA (Ning Chen) CLS staff, L. Ribaud (APS), J. Maley (SSRC), and J. Zimmer (SRC), D.Li and J. De Yoreo(LBNL-now PNNL).

• Questions or Comments.

• Thank you. 27

Appendix

28

29

Sample Origin: Key Lake’s Bulk Neutralization Process

30

Deilmann Tailings Management Facility

+As

Mo

Se

Ni

Fe(II)(aq)

Anoxic

????31

EOC’s-Hydrotalcite

EOC’s-Ferrihydrite


U-mill and Tailings

• Materials tested: 1) Synthetic : FH, Fe/As ~ 4 and 30, Fe/Mo 4 and 30, Fe/Ni 30, All

duplicates or triplicates only short term (7 days). Mg-Fe(II)/Al(III)-SO4-CO3 HTLCs.

2) Industrial: Unwashed and washed neutralized Raffinate, unwashed and washed neutralized McArthur derived Tailings, unwashed Deilmann derived Tailings at 2 distinct depths. All duplicates or triplicates short (7 days) and long term (~ 6 months).

• Conditions tested for these samples:1)pH 10 and 0.5mM Fe(II)(aq)

2)pH 8 and 10mM Fe(II)(aq)

3)pH 8 and 0.5mM Fe(II)(aq)

• Techniques applied: ICP-MS, lab and synchrotron based XRD, ATR-IR, Raman, NEXAFS and EXAFS, EMP, TEM-EDX and ED.

Fe (II)(aq)concentrations were chosen at the pH of

interest so to avoid ferrous hydroxide ppt

32




Tailings (unleached residue+FNR)

Final Neutralized Raffinates (FNR) made of

EOC – Ferrihydrite and EOC – MgAlFe

SO4CO

3

Hydrotalcite

EOC-FH

Mg-Al/Fe-SO4/CO

3 HTLC

EOC-MgAlFe

SO4CO

3 HTLC

33

Experimental Approach to Understanding the

Neutralized Raffinate and Tailings

For the synthetic Fe/X and As-FH cases:

The pH was always lower (never buffered),

High As on FH prevented phase transformation, but still released As under all

conditions tested, and low As showed phase transformation and As release and

no re-adsorption of As was observed.

For Mo (high and low) on FH:

All showed phase inhibition properties [only @ pH 10 and 0.5mM Fe(II)(aq) ] as

well as phase transformation, but released notable concentrations of Mo into

solution that was not re-adsorbed at the end of 7-day reaction period.

For Ni on FH:

Phase transformation occurred in all cases (low or high) in addition to Ni

release into solution, however in all cases, the Ni released was, for the most

part, re-adsorbed back into the solid phase at the end of the 7-day reaction.

Summary: Reductive dissolution behavior of synthetic

X-FH

34

0 2 4 6 8 10 12 14 160

1800

3600

5400

0

180

360

540

0

180

360

540

0

180

360

540

160

320

480

640

0 2 4 6 8 10 12 14 16

(003)

(006)(009)

(113)(110)

Two theta ( =0.41A)

Mg-Al HTLC

(OO3)

Washed Raffinate (with Ba)

(OO3)

Washed Raffinate (No Ba)

Reacted Raffinate (No Ba) pH 8 and 10mM

Reacted Raffinate (No Ba) pH 10 and0.5mM

Reductive dissolution behavior of neutralized

Raffinates (pH 8, 7 days, 10 mM Fe(II)(aq))

1000 1500 2000 2500 3000 3500

1000 1500 2000 2500 3000 3500

OH/H2O

CO3

SO4

Unreacted Reacted Raffinate with Ba

Wavenumber (cm-1)

OH/H2O

H2O

Reacted Raffinate (with Ba) pH 8 and 10mM

CO3

SO4

OH/H2O

H2OSO

4

GR (SO4)

OH/H2O

H2OCO

3SO

4

Reacted Raffinate (No Ba) pH 8 and 10mM

OH/H2O

H2O

CO3

SO4

Unreacted Reacted Raffinate No Ba

800 900 1000 1100 1200

800 900 1000 1100 1200

CO3SO

4

Wavenumbers (cm-1)

Unreacted McArthur derived Raffinate

Raman spectra = Mg-Al HTLC

SO4

CO3

Reacted McArthur derived Raffinate at pH 8 and 10mM

SO4

CO3

Oxidized McArthur derived Raffinate at pH 8 and 10mM

Green Rust (SO4)

SO4

35

Unreacted McArthur ore derived Key Lake neutralized Raffinates

• The FH is doped with Mg and Al.

• Conversely, the Mg-Al Hydrotalcite was doped with Fe.

• Both are also highly doped with Si and S (as SO4). 36

Reductive dissolution behavior of neutralized

Raffinates (pH 8, 7 days, 10 mM Fe(II)(aq))

• Both Mg-Al Hydrotalcite and FH are still present along with

the corresponding elements including S (as SO4) and Si.

Mg-Al

Hydrotalcite

FH

37

FH FH

Hydrotalcite

38

Hydrotalcite

Unreacted Neutralized Raffinates

Mg-Al HTLC

New Hex

phase-

GR is Hex

Globular

FH

39


Tailings 40

Raffinate

Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 0.5 mM Fe(II)(aq))

Reductive dissolution behavior of neutralized mill and Tailings (pH 8 and 0.5 mM Fe(II)(aq))

41

Reductive dissolution behavior of neutralized mill and Tailings (pH 10 and 0.5 mM Fe(II)(aq))

42

pH 8-10

[Fe+2]

pH 8 pH 10 pH 10 OriginalOriginal pH 8 Literature

Raffinate and Tailings component transform to

carbonated- sulfate GR (2012-2013)

43

Mo

Se

Ni

EOC’s-

FerrihydriteAs

EOC’s-Hydrotalcite

+

Green Rust Magnetite

Time

National Institute of Nano-Technology (NINT) Collaboration

44

University of Montreal Collaboration

45

Canadian Light Source-SGM, HXMA and SM Collaboration

46*** Dr. Jinru Lin, HXMA.

Reduction solutions preparation

– Preparation of the reacting solutions was conducted (Fe+2

and lime as base) prior to conducting reactions.

– This was important to investigate as it allowed us to observe the [Fe+2] range that we could use before the precipitation of any phases in the reacting solution (e.g. FeOH2, green rust, siderite).

– @ pH 7-8, [Fe+2] ≥ 10mM maybe used.

pH ~

4

pH = 7-

8

pH = 8.5 pH = 10 47

– For the target pH of 10, [Fe+2] ≤ 0.5mM may only be used because the presence of precipitates in the solution was observed.

10 mM 0.85 mM 0.75

mM

0.5 mM0.75

mM0.5 mM

Reduction solutions preparation

48