Metals Removal from Groundwater Using Permeable Reactive

David J.A. Smyth1, David W. Blowes1, Carol J. Ptacek1, Jeff G. Bain1

Department of Earth Sciences, University of Waterloo

Waterloo, ON, N2L 3G1, Canada BC MLARD Workshop, December 2002

Metals Removal from Groundwater Using Permeable Reactive Barriers

(PRBs)

© University of Waterloo 2002

PRBs for Removal of Inorganic Contaminants from Groundwater

• University of Waterloo experience • Blowes, Ptacek and Robertson • Metals, nutrients and water-borne

pathogens • Plume remediation or control • U.S. Patents 5,362,394 5,514,279

5,876,606


Geochemical Barriers for Metals

• Zero-valent iron: reductive precipitation on grain surfaces

• Organic carbon: sulfate reduction, denitrification • BOF Slag: sorption and co-precipitation

phosphate and arsenic • U.S. Patents 5,362,394 5,514,279 5,876,606 • Activated carbon • Limestone (neutralization)

Pilot Scale Installations

USA

Other

Canada

USA

Other

Canada

Full-Scale PRB Installations

n=14 n=21

PRBs for Inorganic Contaminants

United States

Canada

Pilot-Scale Full-Scale

Europe

Australia Europe

Inorganic PRB Sites

Contaminants Treated

Arsenic

PO4

NO3 U

Cr(VI)

Metals and

AMD

Arsenic

PO4

U

Cr(VI)

Metals and

AMD

Pilot Scale Installations Full-Scale PRB Installations

Zero-Valent Iron for Electroactive Metals

• Field Installation: Chromium (VI), Elizabeth City, NC

• Radionuclides (DOE Facilities) • Arsenic, selenium, mercury • Reductive precipitation on grain

surfaces; precipitation or co-precipitation


Elizabeth City Site U.S. EPA Project

• Reference • Blowes, D.W., et al., 1999. An In-Situ Permeable

Reactive Barrier for the Treatment of Hexavalent Chromium and Trichloroethylene in Ground Water: Volume 1 Design and Installation. Volume 2 Performance Monitoring. Volume 3 Multicomponent Reactive Transport Modeling United States Environmental Protection Agency, Cincinnati, OH, Report EPA/600/R-99/095abc.

• http://www.epa.gov/ada/pubs/reports.html


http://www.epa.gov/ada/pubs/reports.html

0 10

meters

N

Cr (mg/L) June 1994

Building 78

Pasquotank River 1.6

<0.01

<0.01 <0.01

<0.01

<0.01

<0.01

<0.01

<0.01

5.6

8.2

0.22

3.8

0.08 <0.01

T.A. Bennett, M.Sc. Thesis, University of Waterloo, 1997

Bui

ldin

g 78

HANGAR 79


Reactive Material

• 150 m3 zero valent iron (280 tons) • 46 m long, 7.3 m deep and 0.6 m wide barrier


One-Pass Continuous Trencher


One-Pass Continuous Trencher

• Depths of < 30 ft • Width 1-2 ft • Very rapid installation • Big equipment • Mobilization


USCG Wall Installation

© University of Waterloo

USCG Wall Installation

-6

-4

-2

Transect 1 (November 1996)

Depth (m)

Groundwater flow direction 0 50 cm

5

6

7

8

9

10

Wall

pH


Dep

th (m

)


-6

-4

-2

Transect 1 (November 1996)

Depth (m)

Groundwater flow direction 0 50 cm

0

0.05

1.0

2.0

Wall

Cr(VI) (mg/L)


Dep

th (m

)


Mineralogical Characterization

• Increased solid-phase carbon • Carbonate mineralogy

• Iron oxyhydroxides • goethite • ferrihydrite • green rust

• Iron Sulfides © University of Waterloo 2002

Long-Term Efficiency (Mayer)

0.0 0.1 0.2 0.3 0.4 0.5distance [m]

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0ϕ F

e[-

]0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

φ[-

]

ϕFe - T = 5 yearsϕFe - T = 10 yearsϕFe - T = 20 yearsφ - T = 5 yearsφ - T = 10 yearsφ - T = 20 years

porosity

volume fraction of secondary minerals

volume fraction ofzero-valent iron


1) Reduction and Co-precipitation with Goethite i) 4Fe0

(s) + 3O2(g) + 6H20(l) 4Fe3+(aq) + 120H-

(aq)

ii) Fe3+(aq) + H3AsO3(aq) + 2H20(l) FeO(OH,H2AsO4)(s) + 5H+

(aq)

2) Sulphate Reduction

i) 4Fe0(s) + SO4

2-(aq) + 10H+

(aq) H2S(aq) + 4Fe2+(aq)

+ 4H2O(l)

ii) 2As3+(aq) + 3H2S(aq) As2S3(s) + 6H+

(aq)

3) Adsorption

ARSENIC Mechanisms for Removal


McRae (1999): Arsenic Removal Mechanisms

• Energy Dispersive X-Ray Analysis • As present in grain coatings and

possibly on zero-valent iron grain surface

• X-Ray Photoelectron Spectroscopy • As(III) predominant in solid phase • Reductive precipitation and co-

precipitation with goethite in coatings © University of Waterloo 2002

Column Experiments


Zero Valent Iron Column

Pore Volumes

0 20 40 60 80 100 120

As

(µg/

L)

0

200

400

600

800

1000

Input = 1000 µg/L


Pore Volumes0 5 10 15 20 25 30

Ars

enic

(mg/

L)

0

5

10

15

Arsenic Concentration in 100% Iron Column

Note: Detection Limit is 0.005mg/L Influent Effluent


Total Arsenic Concentration Profiles in ZVI Column Mine Groundwater at Velocity of 6.75 cm/day

Distance into Iron (cm)

0 5 10 15 20 25 30 35

Ars

enic

Tot

(mg/

L)

0

1

2

3

4

5

6 Profile after 29.6 PV Profile after 37.5 PV


Sulfate-Reduction PRBs • Metals in sulfate rich water- AMD • Sulfate reduction is microbially mediated

process • Purpose of PRB is to intercept

groundwater flow and enhance sulfate reduction

• Generation of H2S and precipitation of metal sulfide minerals

• Decrease acid-generating potential; remove dissolved metals © University of Waterloo 2002

Acid Mine Drainage and Sulfate Reduction

FeS2(s) + 7/2O2 + H2O => Fe2+ + 2SO42- + 2H+

Fe2+ 1/4O2 + 5/2H2O => Fe(OH)3(s)+2H+

SO42- + 2CH2O => H2S +2HCO3

-

Fe2+ + H2S => FeS + 2H+

Tailings Dam

Sulfate Reduction

Sulfide Oxidation

Iron Oxidation

Reactive Wall


Nickel Rim Mine, Sudbury, ON

• Laboratory batch and column study • Predictive groundwater flow

modelling • Field installation (1995) • Benner et al., 1997; 1999 • Waybrant et al., 1998


Reactive Mixture Composition for PRB

Leaf Compost Municipal

Compost

Wood Chips

Limestone


Bedrock

Sand

Sand

Reactive Material

Direction of Groundwater flow

4 m 8 m

3.6 m

15 m

Porous Reactive Wall Installation



Nickel Rim Wall Materials


NR Wall Installation

Sand

Sand

Compost


Nickel Rim Wall

Clay Cap


Nickel Rim Wall

>350 250-350 150-249 50-149 <50

>350 250-350 150-249 50-149 <50

surface water recharge

? ?

material sand sand reactive

meters

0 5 m

Chloride (mg/L) June 96

Chloride (mg/L) Nov. 95

groundwater flow direction

Benner et al., 1997

Groundwater Flow


Benner et al., 1997

Acid Generating Potential (meq/L)

Sulfate (mg/L)

Iron (mg/L)


meters

0 5 m reactive material sand sand

>20 10 - 20 0.0 - 10 -10 - 0.0 <-10

>2000 1500-2000 1000-1499 500-999 <500

>350 250-350 150-249 50-149 <50

Treatment Results


Sulfate Reduction in PRB

• Decreasing sulfate concentrations • Sulfate-reducing bacteria • Dissolved sulfide present • Isotopic enrichment of 34S in remnant

sulfate • Iron monosulfides identified in cores


reactive material sand sand

groundwater flow direction 0 15 feet

0 5 meters

Sulfate (mg/L)

August 2001

4900

4720

3400

2940

4370

2950

2834

3430

1561

2188

1086

379

2497

57

1995

2036

1960

1992

2746

2558

3708

2652

2483

2870 2687

4190

2578

3408

2620

2549

2439

2229

2156

2726

2212

2473

3054 2289

2510

2240

2424

2551

3026

2812

> 3500 2500- 3500 1500- 2499 500- 1499 < 500

2900

3202

2000

1936 3

R W

2 1

R W

2 3

R W

2 9

R W

3 0

R W

2 6

R w

3 1

1

2

3

4

1

2

3

4

3

1

2

4

2

4

3

1

3

4

2

1

1

2

3

4

1

2

3

4

R W

3 6

R W

3 2

R W

3 3

R W

3 4

R W

3 5

2

3

4

1

2

3

4

1

2

3

4

1

2

4

1

2

3

4

R W

2 8

0 0

5 5

meters

reactive material sand sand


712

1258

654

356

978

369

672

19.7

114

105

3.78

299

448

.86

383

222

165

478

404

547

302

893

461

248 358

526

633

323 263

772

441

265

295

148

457 270

290

245

724

383

158

135

309

912

605 528

441

0- 499 500- 999 1000- 1499 1500- 1999 > 2000

3

R W

2 1

R W

2 3

R W

2 9

R W

3 0

R W

2 6

R w

3 1

1

2

3

4

1

2

3

4

3

1

2

4

2

4

3

1

3

4

2

1

1

2

3

4

1

2

3

4

R W

3 6

R W

3 2

R W

3 3

R W

3 4

R W

3 5

2

3

4

1

2

3

4

1

2

3

4

1

2

4

1

2

3

4

R W

2 8

0 0

5 5

meters

0 15 feet

0 5 meters

Iron (mg/L) August 2001

Sulfide Accumulation in Nickel Rim PRB (Daignault 2002, UW B.Sc.Thesis)

0

10

20

30

40

50

60

70

80

90

0 10 20 30 40 50 60 70 80 90

Time (months)

Rate

(µ

mo

l S

cm

-3 a

-1) Up-gradient core (NRW29)

Mid-gradient core (NRW30)

Down-gradient core (NRW31)

Summary of Nickel Rim PRB • The reactive wall is removing significant

portion of the dissolved iron from the plume; full treatment would have required thicker PRB with longer residence time

• Reduced flux of contaminants in groundwater; reduced acid-generating potential of groundwater in receiving surface water

• Cost for materials and installation approximately $25 K (US) in 1995


Issues • Heterogeneities in PRB/ residence

time of contaminated groundwater in PRB is critical to level of treatment achieved

• Some loss of reactivity with time; sustained availability of organic carbon

• Influence of temperature in shallow PRB systems © University of Waterloo 2002

STEEL PRODUCTION WASTES Basic Oxygen Furnace (BOF) Slag • Steel production waste product • Used as aggregate for construction • High Ca and Fe oxides and

hydroxides • Interaction with water: high pH • Removal of phosphate (Baker et al.,

1997; 1998) and arsenic(McRae et al., 1999)


BOF-Oxide

Zero Valent Iron

Activated Alumina

Silica Sand

Limestone

Solid Reactive Mixtures

Aquifer Materials Reactive Materials

Batch Removal Rates

Time (h)

0 2 4 6 8

0

200

400

600

800

1000

As(III) + As(V)

Time (h)

0 2 4 6 8

0

200

400

600

800

1000

Se(VI)

Se(

VI) (µg

/L)

Asto

tal (µg

/L)

Iron Slag

BOF Slag Column

Pore Volumes

0 50 100 150 200

As (µ

g/L)

0

200

400

600

800

1000

1200

As(total)

Second Column Test

• 50 % BOF slag/ 50 % gravel • Low pH site groundwater with 4 mg/L

arsenic • More than 75 pore volumes of flow

(velocity of 0.3 m/day) • Total arsenic concentration in

effluent less than 0.01 mg/L

Arsenic Removal by BOF Slag

• Removal of arsenic oxyanions by sorption iron and manganese oxyhydroxides in BOF

• Removal to low levels (<0.005 mg/L total arsenic)

• Sustained performance for 100 pore volumes of 10 % BOF mixture

North Bay System: pH with Time

Days of Operation0 200 400 600 800 1000

pH

0

2

4

6

8

10

12

14

Septic System pH with Time Sand-Filter pH with TimeBOF Chamber pH with Time

North Bay System: E-Coli with Time

Days of Operation0 200 400 600 800 1000

E-C

oli (

CFU

per

100

mL)

1e-1

1e+0

1e+1

1e+2

1e+3

1e+4

1e+5

E-Coli in Raw Water E-Coli in Sand Filter E-Coli in BOF Filter

BOF-Chamber Performance • Effective removal of phosphorus • Effective removal of E-Coli

• Elevated pH provides environment that eliminates bacteria

• Elevated pH of 12 or higher • Elevated pH is buffered by soils and sediments

upon release to subsurface • pH of groundwater approximately 1 m down-

gradient of discharge gallery was 6.2 to 7 (August 2000)


Zero-Valent Iron and Other Reactive Materials

• Excellent removal of electroactive metals

• Sulfate reduction and AMD treatment • Excellent treatment of nutrients • Performance of field-scale applications • Removal mechanisms • Reactive capacity • Formation of secondary precipitates


Documents

Metals Removal from Groundwater Using Permeable Reactive