Transcript Raffinate neutralization experiments UMH_II3

Raffinate Neutralization Experiments
at the McClean Lake Mill –
Removal of Arsenic and Nickel
John Mahoney

Hydrologic Consultants, Inc.,
143 Union Blvd., Suite 525, Lakewood, Colorado, USA

Donald Langmuir
Hydrochem Systems Corp., Denver, Colorado, USA

Maynard Slaughter
Crystal Research Laboratories, Greeley, Colorado, USA

John Rowson
COGEMA Resources, Saskatoon, Saskatchewan, Canada
Location Map
Overview

Arsenic and Nickel Bearing Uranium Ores

Tailings disposal issues

Raffinate 300-700 mg/L As, 200-500 mg/L
Ni, pH~1.0

Diffusion of As into Fox Lake required As
and Ni in tailings pore waters be ~ 1 mg/L
Mill and JEB TMF
Tailings Disposal System
Tailings Optimization and
Validation



License Application - Initial model based on
mineral precipitation (scorodite) and surface
complexation of As on Hydrous Ferric Oxide
(Langmuir et al., 1999)
Demonstrated that As < 1 mg/L was possible
Tailings Optimization and Validation Program
(TOVP) ongoing studies to



Verify and improve process,
Monitor tailings management facility, and
Validate model assumptions
Tailings Neutralization

Tailings neutralization circuit increases
Fe:As > 3

Ferric sulfate is used to increase Fe:As

Neutralization by slaked lime

Two stage process


pH 4 first tank
pH 7 - 8 second tank
Tailings Neutralization Circuit
Raffinate
Fe 2 (SO 4 ) 3
CaO (pH 8)
Tailings
CaO (pH 4)
BaCl
2
Flocculant
pH
pH
NEUTRALIZATION TANKS
MIXING TANK
THICKENER
Process Air
to TMF
24 hour metallurgical
composite sample
Raffinate Neutralization
Experiments

Plant raffinate spiked ~ 700 mg/L As, 500 mg/L Ni







Ferric sulfate added
Dry Lime (CaO), slaked lime (Ca(OH)2, or NaOH
Some experiments included leach residue
Short duration to simulate residence times in
Neutralization Circuit
Filtered samples - solution analyses
Solids air dried - mineralogical analysis
Raffinate 2 series, Redox measurements, single
beaker experiments
Setup
Raffinate Compositions
(mg/L)
Parameter
Raffinate 1
Unspiked
pH
Total As
362
Raffinate 1
Raffinate 2
Raffinate 2
Unspiked
1.5
1.1
732 (920)
693 (729)
Sum of As (III+V)
351
668
As(III)
100
447
As (V)
251
221
808
1,854 (2,400)
640
685
Fe Total
629
2,400 (2,700)
Fe (II)
Al
420
200
Ca
760
589
Na
48
23
Sulfate
14,100
21,430
Ni
203
560 (550)
230
668
Eh (mv)
Fe/As
515 (529)
NA
4.4
NA
3.6
Neutralization Tests at pH Values of 2.2 to
7.4 (right to left) Beaker on Far Left is
Slurried Lime)
Samples 9-27-5 and 6
Filter Cake Wet
Mineralogy Studies

X-ray diffraction

SEM with Energy Dispersive Spectrometry

Chemical analysis, mainly XRF, Fe(II)

EXAFS- Canadian Light Source and Argonne APL

Microprobe (electron beam, synchronous
radiation)

Quantitative mineralogy - XRD, analysis
Single Beaker Tests

Raffinate 2

Separated mineral precipitates rather than
accumulate all precipitates

Enhanced X-ray diffraction determinations

Initial volume of solution ~ 5 L

Three solution samples collected

Four solid samples
Single Beaker Experiment
Single Beaker, #1 First Filter Cake
Single Beaker #4 Wet Product
Arsenic Concentrations as Function of pH
1000
Raffinates
As (mg/L)
100
10
1
0.1
0.01
0
1
2
3
4
5
6
7
8
9
pH before filtering
Raffinate 1
Raff 1 Slaked Lim e Leach Residue
Raff 1 Ca(OH)2 No Residue
Raff 1 Na(OH) Leach Residue
Raff 1 Na(OH) No Residue
Raff 1 Slaked Lim e No Residue
Raffinate 2
Raff 2 Slaked Lim e No Residue
Raff 2 Slaked Lim e Single Beaker
Nickel Removal
600
Raffinates
500
Ni (mg/L)
400
300
200
100
0
0
1
2
3
4
5
6
7
8
pH before filtering
Raffinate 1
Raff 1 Ca(OH)2 No Residue
Raff 1 Na(OH) No Residue
Raff 1 Slaked Lim e Leach Residue
Raff 1 Na(OH) Leach Residue
Raff 1 Slaked Lim e No Residue
Raffinate 2
Raff 2 Slaked Lim e No Residue
Raff 2 Slaked Lim e Single Beaker
9
Solution Concentrations
100,000.000
Concentrations of Major Components for Slaked Lime Neutralization of Raffinate 2
Concentration (mg/L)
10,000.000
1,000.000
100.000
10.000
Raffinate 2
1.000
SB-2
0.100
SB-3
0.010
SB-4
0.001
0
1
2
5
4
3
7
6
pH before filtering
Total As
Total Fe
Al
Si
Sulfate
Ni
SB As
SB Fe
SB Al
SB Si
SB Sulfate
SB Ni
8
Molar Amounts Removed from Solution
Raffinate 2
0.035
pH = 7.32
Comparison with Residual
0.03
pH = 6.24
0.025
pH = 5.29
Moles
pH = 4.09
pH = 3.23
0.02
0.015
0.01
pH = 2.18
0.005
0
Spiked
raffinate
Sample 927-1
Sample 927-2
Sample 927-3
Sample 927-4
Sample
As
Fe
Ni
Fe(II)
Sample 927-5
Sample 927-6
Remains in
Solution
Saturation Indices
(based upon As (V) and Fe(III) concentrations)
5
Crystalline
Scorodite
0
Saturation Index
Gypsum
Amorphous
Scorodite
-5
Ferrihydrite
-10
Theophrastite
-15
Annabergite
-20
0
1
2
3
4
5
6
pH
Gypsum
Ni(OH)2
Ni3(AsO4)2:8H2O
Ferrihydrite
Scorodite-cr
Scorodite-am
7
8
Ion Activity Products
-20.0
-25.0
Scorodite
IAP
-30.0
-35.0
Ferrihydrite
-40.0
-45.0
0.00
2.00
4.00
pH
6.00
8.00
Eh-pH diagram for the systems Fe – As – O – H based upon
stabilities of scorodite and ferrihydrite using speciated
As and Fe data from the Raffinate 2 neutralization experiments
1.5
25°C
1
3+
Fe
O 2 (g)
Scorodite
-log K = 23.97
H2O(l)
Eh (v)
0.5
Ferrihydrite
- log K
= 33.33
2+
Fe
H 2 O(l)
0
H2(g)
-0.5
-1
0
2
4
6
pH
8
10
Geochemical Model

PHREEQC used


Disequilibrium steps included to explain removal of Ni at
low pH


Ferric arsenate complexes included in database
Force fit
Simple mineral precipitation reactions

Gypsum – Sulfate [CaSO4 • 2H2O]

Scorodite (Ksp adjusted) – Fe and As to pH ~5 [FeAsO4 • 2H2O]

Ferrihydrite/Green Rust II- Iron Fe(OH)3 / Fe3(OH)8

Theophrastite – Nickel [Ni(OH)2]

Annabergite – Nickel [Ni3(AsO4)2 • 8H2O]

Basaluminite – Aluminum [Al4SO4 (OH)10 • nH2O]
Tailings Neutralization Process
Initial Reaction
McClean Lake Operation
Solution pH 1.5
Analyte
(mg/L) (% prec.)
Al
420
0.0
As
732
0.0
Fe
2,400
0.0
Ni
560
0.0
Si
260
0.0
Tailings Neutralization Process
pH Gradient
McClean Lake Operation
Solution pH 1.5
Analyte
(mg/L) (% prec.)
Al
420
0.0
As
659
~10
Fe
2,328
~3
Ni
532
~5
Si
260
0.0
Tailings Neutralization Process
Bulk Neutralization
McClean Lake Operation
Solution pH 2.2
Analyte
(mg/L) (% prec.)
Al
420
0.0
As
150
79.5
Fe
1,600
33.3
Ni
500
10.7
Si
260
0.0
Tailings Neutralization Process
Bulk Neutralization
McClean Lake Operation
Solution pH 4.0
Analyte
(mg/L) (% prec.)
Al
290
31.0
As
0.5
99.9
Fe
570
76.3
Ni
450
19.6
Si
140
46.2
Tailings Neutralization Process
Bulk Neutralization
McClean Lake Operation
Solution pH 6.1
Analyte
(mg/L) (% prec.)
Al
0.5
99.9
As
0.08
100.0
Fe
340
85.8
Ni
250
55.4
Si
17
93.5
Tailings Neutralization Process
Bulk Neutralization
McClean Lake Operation
Solution pH 7.4
Analyte
(mg/L) (% prec.)
Al
0.5
99.9
As
0.06
100.0
Fe
2.2
99.9
Ni
1.3
99.8
Si
3.2
98.8
Tailings Neutralization Process
Aging
McClean Lake Operation
Solution pH 7.4
Analyte
(mg/L) (% prec.)
Al
0.5
99.9
As
0.06
100.0
Fe
2.2
99.9
Ni
1.3
99.8
Si
3.2
98.8
Flow Diagram
RAFFINATE
EQUILIBRATE
pH = 1.5
pe = 11.88
As = 747 mg/L
Ni = 571 mg/L
Fe = 2,450 mg/L
SOLUTION 11
pH = 7
Ni3(AsO4)2 • 8H2O
FERRIHYDRITE
90%
MIX
RAFFINATE
SOLUTION 11
EQUILIBRATE
pH = 2.18
SCORODITE
GYPSUM
MODEL SOLUTION 6-1
pH = 2.18
pe = 11.7
As = 64.7 mg/L
Ni = 518 mg/L
Fe = 1,830 mg/L
pH = 7
As = 291 mg/L
Ni = 35.8 mg/L
Fe = 554 mg/L
10%
Comparison Data and Model
10,000.00
Fe
1,000.00
Concentration (mg/L)
Ni
100.00
10.00
As
1.00
0.10
0.0
1.0
2.0
3.0
4.0
5.0
6.0
pH
As
Model As
Fe
Model Fe
Ni
Model Ni
7.0
8.0
Comparison Data and Model
100,000.00
Concentration (mg/L)
10,000.00
Sulfate
1,000.00
Fe
Ni
100.00
10.00
As
1.00
0.10
Al
0.01
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
pH
As
Model As
Fe
Model Fe
Al
Model Al
Sulfate
Model Sulfate
Ni
Model Ni
8.0
Conclusions

Scorodite is dominant As - bearing phase




As concentrations < 1 mg/L



Balance between relatively stable scorodite and less
stable ferrihydrite
Adjustments to Ksp produce best fit
Precipitation stops by pH ~ 5
Little or no evidence of As sorption process
Disequilibrium removes some nickel
Nickel mainly in theophrastite


Model concentrations higher than measured
Sorption may also play a role