CONTROLS OF TOXIC ELEMENTS IN ABIOTIC REDUCTIVE DISSOLUTION OF URANIUM MILL RAFFINATES AND TAILINGS...
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Transcript of 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.
Experimental Approach to Understanding the Neutralized
Raffinates and Tailings
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
Final Neutralized Deilmann and McArthur
Tailings (FNT)
Final Neutralized Raffinates (FNR)
EOC-FH
Mg-Al/Fe-SO4/CO
3 HTLC
EOC-MgAlFe
SO4CO
3 HTLC
10
Experimental Approach to Understanding the Neutralized
Raffinates and Tailings
Gomez et al. RSC Advances.
2013, 3, 25812-22.
Selected Key Lake Bulk Neutralization Process Samples
Gomez et al. Environ. Sci. Technol. 2013, 47, 7883-7891.
13
As K-edge EXAFS Data on the McArthur ore
Key Lake Final Neutralized Raffinates (pH 10) and process step
samples at pH 4 and 6
Key Lake Final Neutralized Raffinate
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
As K-edge EXAFS Data on the McArthur ore
Key Lake Final Neutralized Raffinates at pH 10 and process
sample at pH 10
Key Lake Final Neutralized Raffinate
at pH 10
AsO4 adsorbed Hydrotalcite
Data collection and fitting done by
Dr. Jinru Lin
15
N2(g)
N2(g
)
Raman
XANES EXAFS
TEM
Experimental Approach to Understanding the Neutralized
Raffinates and Tailings
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))
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
Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 10 mM Fe(II)(aq))
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
Reacted Key Lake Final Neutralized
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)
Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 10 mM Fe(II)(aq))
• 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
Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 10 mM Fe(II)(aq))
Magnetite Formation
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
Reacted Key Lake Final Neutralized
Raffinate at pH 10 and 6 months
Reacted Key Lake Final Neutralized
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
+As
Mo
Se
Ni
Fe(II)(aq)
Anoxic
????31
EOC’s-Hydrotalcite
EOC’s-Ferrihydrite
Experimental Approach to Understanding the Neutralized
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
Experimental Approach to Understanding the Neutralized
Raffinates and Tailings
Final Neutralized Deilmann and McArthur
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
Mg-Al HTLC
New Hex
phase-
GR is Hex
Globular
FH
39
Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 10 mM Fe(II)(aq))
Tailings 40
Raffinate
Reductive Dissolution of Neutralized Raffinates and Tailings (pH 8 and 0.5 mM Fe(II)(aq))
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
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