Raffinate Neutralization Raffinate Neutralization Experiments at the McClean Lake Experiments at the McClean Lake

Mill –Mill –Removal of Arsenic and NickelRemoval 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 SlaughterCrystal Research Laboratories, Greeley, Colorado, USA

John RowsonCOGEMA Resources, Saskatoon, Saskatchewan, Canada

Location MapLocation Map

OverviewOverview

Arsenic and Nickel Bearing Uranium OresArsenic and Nickel Bearing Uranium Ores

Tailings disposal issuesTailings disposal issues

Raffinate 300-700 mg/L As, 200-500 mg/L Ni, Raffinate 300-700 mg/L As, 200-500 mg/L Ni, pH~1.0pH~1.0

Diffusion of As into Fox Lake required As and Diffusion of As into Fox Lake required As and Ni in tailings pore waters be ~ 1 mg/LNi in tailings pore waters be ~ 1 mg/L

Mill and JEB TMFMill and JEB TMF

Tailings Disposal SystemTailings Disposal System

Tailings Optimization and Tailings Optimization and Validation Validation

License Application - Initial model based on License Application - Initial model based on mineral precipitation (scorodite) and surface mineral precipitation (scorodite) and surface complexation of As on Hydrous Ferric Oxide complexation of As on Hydrous Ferric Oxide (Langmuir et al., 1999)(Langmuir et al., 1999)

Demonstrated that As < 1 mg/L was possibleDemonstrated that As < 1 mg/L was possible

Tailings Optimization and Validation Program Tailings Optimization and Validation Program (TOVP) ongoing studies to (TOVP) ongoing studies to Verify and improve process, Verify and improve process, Monitor tailings management facility, andMonitor tailings management facility, and Validate model assumptionsValidate model assumptions

Tailings NeutralizationTailings Neutralization

Tailings neutralization circuit increases Fe:As > 3Tailings neutralization circuit increases Fe:As > 3

Ferric sulfate is used to increase Fe:AsFerric sulfate is used to increase Fe:As

Neutralization by slaked limeNeutralization by slaked lime

Two stage process Two stage process pH 4 first tank pH 4 first tank pH 7 - 8 second tankpH 7 - 8 second tank

Tailings Neutralization CircuitTailings Neutralization Circuit

to TMF

24 hour metallurgical composite sample

Raffinate Tailings BaCl 2

Fe 2 (SO 4 ) 3

CaO (pH 4)

pH pH

THICKENER

NEUTRALIZATION TANKS

Flocculant

CaO (pH 8)

MIXING TANK

Process Air

Raffinate Neutralization Raffinate Neutralization ExperimentsExperiments

Plant raffinate spiked ~ 700 mg/L As, 500 mg/L Plant raffinate spiked ~ 700 mg/L As, 500 mg/L NiNi Ferric sulfate addedFerric sulfate added Dry Lime (CaO), slaked lime (Ca(OH)Dry Lime (CaO), slaked lime (Ca(OH)22, or NaOH, or NaOH Some experiments included leach residueSome experiments included leach residue Short duration to simulate residence times in Short duration to simulate residence times in

Neutralization CircuitNeutralization Circuit Filtered samples - solution analysesFiltered samples - solution analyses Solids air dried -Solids air dried - mineralogical analysismineralogical analysis

Raffinate 2 series, RedoxRaffinate 2 series, Redox measurements, measurements, single beaker experimentssingle beaker experiments

SetupSetup

Raffinate CompositionsRaffinate Compositions (mg/L)(mg/L)

Parameter Raffinate 1 Unspiked

Raffinate 1

Raffinate 2 Raffinate 2

Unspiked

pH   1.5   1.1

Total As 362 732 (920)   693 (729)

Sum of As (III+V)     351 668

As(III)     100 447

As (V)     251 221

Fe Total 629 2,400 (2,700) 808 1,854 (2,400)

Fe (II)     640 685

Al   420   200

Ca   760   589

Na   48   23

Sulfate   14,100   21,430

Ni 203 560 (550) 230 515 (529)

Eh (mv)       668

Fe/As NA 4.4 NA 3.6

Neutralization Tests at pH Values of Neutralization Tests at pH Values of 2.2 to 7.4 (right to left) Beaker on Far 2.2 to 7.4 (right to left) Beaker on Far

Left is Slurried Lime)Left is Slurried Lime)

Samples 9-27-5 and 6Samples 9-27-5 and 6

Filter Cake WetFilter Cake Wet

Mineralogy StudiesMineralogy 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 TestsSingle 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 ExperimentSingle Beaker Experiment

Single Beaker, #1 First Filter Single Beaker, #1 First Filter CakeCake

Single Beaker #4 Wet ProductSingle Beaker #4 Wet Product

Arsenic Concentrations as Function Arsenic Concentrations as Function of pHof pH

0.01

0.1

1

10

100

1000

0 1 2 3 4 5 6 7 8 9

pH before filtering

As

(m

g/L

)

Raffinate 1 Raff 1 Ca(OH)2 No Residue Raff 1 Na(OH) No Residue

Raff 1 Slaked Lime Leach Residue Raff 1 Na(OH) Leach Residue Raff 1 Slaked Lime No Residue

Raffinate 2 Raff 2 Slaked Lime No Residue Raff 2 Slaked Lime Single Beaker

Raffinates

Nickel RemovalNickel Removal

0

100

200

300

400

500

600

0 1 2 3 4 5 6 7 8 9

pH before filtering

Ni

(mg

/L)

Raffinate 1 Raff 1 Ca(OH)2 No Residue Raff 1 Na(OH) No Residue

Raff 1 Slaked Lime Leach Residue Raff 1 Na(OH) Leach Residue Raff 1 Slaked Lime No Residue

Raffinate 2 Raff 2 Slaked Lime No Residue Raff 2 Slaked Lime Single Beaker

Raffinates

Solution ConcentrationsSolution Concentrations

Concentrations of Major Components for Slaked Lime Neutralization of Raffinate 2

0.001

0.010

0.100

1.000

10.000

100.000

1,000.000

10,000.000

100,000.000

0 1 2 3 4 5 6 7 8

pH before filtering

Co

nc

en

tra

tio

n (

mg

/L)

Total As Total Fe Al Si Sulfate Ni

SB As SB Fe SB Al SB Si SB Sulfate SB Ni

Raffinate 2

SB-2

SB-3

SB-4

Molar Amounts Removed from Molar Amounts Removed from SolutionSolution

Raffinate 2Raffinate 2Comparison with Residual

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

Spikedraffinate

Sample 9-27-1

Sample 9-27-2

Sample 9-27-3

Sample 9-27-4

Sample 9-27-5

Sample 9-27-6

Remains inSolution

Sample

Mo

les

As Fe Ni Fe(II)

pH = 2.18

pH = 3.23pH = 4.09

pH = 5.29

pH = 6.24

pH = 7.32

Saturation IndicesSaturation Indices(based upon As (V) and Fe(III) concentrations)(based upon As (V) and Fe(III) concentrations)

-20

-15

-10

-5

0

5

0 1 2 3 4 5 6 7 8

pH

Sa

tura

tio

n In

de

x

Gypsum Ni(OH)2 Ni3(AsO4)2:8H2O Ferrihydrite Scorodite-cr Scorodite-am

Annabergite

Theophrastite

Ferrihydrite

Amorphous Scorodite

Gypsum

Crystalline Scorodite

Ion Activity ProductsIon Activity Products

-45.0

-40.0

-35.0

-30.0

-25.0

-20.0

0.00 2.00 4.00 6.00 8.00

pH

IAP

Scorodite

Ferrihydrite

Eh-pH diagram for the systems Fe – As – O – H based upon Eh-pH diagram for the systems Fe – As – O – H based upon stabilities of scorodite and ferrihydrite using speciatedstabilities of scorodite and ferrihydrite using speciated

As and Fe data from the Raffinate 2 neutralization As and Fe data from the Raffinate 2 neutralization experimentsexperiments

-1

-0.5

0

0.5

1

1.5

0 2 4 6 8 10

pH

Eh

(v)

Fe2+

Fe3+

Scorodite-log K = 23.97

H 2O(l)

H2O(l)

O 2 (g)

H2(g)

25°C

Ferrihydrite- log K = 33.33

Geochemical ModelGeochemical Model PHREEQCPHREEQC used used

Ferric arsenate complexes included in database Ferric arsenate complexes included in database Disequilibrium steps included to explain removal of Disequilibrium steps included to explain removal of

Ni at low pHNi at low pH Force fitForce fit

Simple mineral precipitation reactionsSimple mineral precipitation reactions

Gypsum – Sulfate [CaSOGypsum – Sulfate [CaSO4 4 • • 2H2H22O]O]

Scorodite (Ksp adjusted) – Fe and AsScorodite (Ksp adjusted) – Fe and As to pH to pH ~5~5 [FeAsO [FeAsO4 4 • •

2H2H22O]O]

Ferrihydrite/Green Rust II- IronFerrihydrite/Green Rust II- Iron Fe(OH)Fe(OH)3 3 // FeFe33(OH)(OH)88

Theophrastite – NickelTheophrastite – Nickel [Ni(OH)[Ni(OH)22]]

Annabergite – Nickel [NiAnnabergite – Nickel [Ni33(AsO(AsO44))22 • • 8H8H22O]O]

Basaluminite – Aluminum Basaluminite – Aluminum [Al[Al44SOSO4 4 (OH)(OH)10 10 • • nHnH22O]O]

Tailings Neutralization ProcessTailings Neutralization ProcessInitial ReactionInitial Reaction

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

420

732

2,400

560

260

0.0

0.0

0.0

0.0

0.0

Solution pH 1.5

McClean Lake OperationMcClean Lake Operation

Tailings Neutralization ProcessTailings Neutralization ProcesspH GradientpH Gradient

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

420

659

2,328

532

260

0.0

~10

~3

~5

0.0

Solution pH 1.5

McClean Lake OperationMcClean Lake Operation

Tailings Neutralization ProcessTailings Neutralization Process Bulk NeutralizationBulk Neutralization

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

420

150

1,600

500

260

0.0

79.5

33.3

10.7

0.0

Solution pH 2.2

McClean Lake OperationMcClean Lake Operation

Tailings Neutralization ProcessTailings Neutralization ProcessBulk NeutralizationBulk Neutralization

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

290

0.5

570

450

140

31.0

99.9

76.3

19.6

46.2

Solution pH 4.0

McClean Lake OperationMcClean Lake Operation

Tailings Neutralization ProcessTailings Neutralization Process Bulk NeutralizationBulk Neutralization

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

0.5

0.08

340

250

17

99.9

100.0

85.8

55.4

93.5

Solution pH 6.1

McClean Lake OperationMcClean Lake Operation

Tailings Neutralization ProcessTailings Neutralization Process Bulk NeutralizationBulk Neutralization

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

0.5

0.06

2.2

1.3

3.2

99.9

100.0

99.9

99.8

98.8

Solution pH 7.4

McClean Lake OperationMcClean Lake Operation

Tailings Neutralization ProcessTailings Neutralization ProcessAgingAging

Analyte (mg/L) (% prec.)

Al

As

Fe

Ni

Si

0.5

0.06

2.2

1.3

3.2

99.9

100.0

99.9

99.8

98.8

Solution pH 7.4

McClean Lake OperationMcClean Lake Operation

Flow DiagramFlow Diagram

RAFFINATEpH = 1.5pe = 11.88As = 747 mg/LNi = 571 mg/LFe = 2,450 mg/L

EQUILIBRATEpH = 7

Ni3(AsO4)2 • 8H2OFERRIHYDRITE

SOLUTION 11pH = 7As = 291 mg/LNi = 35.8 mg/LFe = 554 mg/L

MIXRAFFINATE

SOLUTION 11

MODEL SOLUTION 6-1pH = 2.18pe = 11.7As = 64.7 mg/LNi = 518 mg/LFe = 1,830 mg/L

EQUILIBRATEpH = 2.18

SCORODITEGYPSUM

90% 10%

Comparison Data and ModelComparison Data and Model

0.10

1.00

10.00

100.00

1,000.00

10,000.00

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

pH

Co

nc

en

tra

tio

n (

mg

/L)

As Model As Fe Model Fe Ni Model Ni

Fe

Ni

As

Comparison Data and ModelComparison Data and Model

0.01

0.10

1.00

10.00

100.00

1,000.00

10,000.00

100,000.00

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

pH

Co

ncen

tratio

n (m

g/L

)

As Model As Fe Model Fe Al Model Al Sulfate Model Sulfate Ni Model Ni

Sulfate

Fe

Al

Ni

As

ConclusionsConclusions

Scorodite is dominant As - bearing phaseScorodite is dominant As - bearing phase Balance between relatively stable scorodite and less Balance between relatively stable scorodite and less

stable ferrihydritestable ferrihydrite Adjustments to Ksp produce best fitAdjustments to Ksp produce best fit Precipitation stops by pH ~ 5Precipitation stops by pH ~ 5

As concentrations < 1 mg/LAs concentrations < 1 mg/L Little or no evidence of As sorption processLittle or no evidence of As sorption process Disequilibrium removes some nickelDisequilibrium removes some nickel

Nickel mainly in theophrastiteNickel mainly in theophrastite Model concentrations higher than measuredModel concentrations higher than measured Sorption may also play a roleSorption may also play a role