Geochemistry of extremely alkaline ph 12 ground water in slag fill aquifers
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Geochemistry of Extremely Alkaline (pH > 12) Ground water in Slag–Fill Aquifers. By Austin Krabbenhoft 11/29/10. Lake Calumet - Chicago. The Problem. Ground water is among the most degraded in Illinois ( Roadcap, Walton, & Bethke, 2005)

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Geochemistry of Extremely Alkaline (pH > 12) Ground water in Slag–Fill Aquifers

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Geochemistry of extremely alkaline ph 12 ground water in slag fill aquifers

Geochemistry of Extremely Alkaline (pH > 12) Ground water in Slag–Fill Aquifers

By Austin Krabbenhoft

11/29/10


Lake calumet chicago

Lake Calumet - Chicago


The problem

The Problem

  • Ground water is among the most degraded in Illinois (Roadcap, Walton, & Bethke, 2005)

  • Has a high pH (>12), high total dissolved solids, and high ammonia (>50 mg/L)

  • High levels of Ba, Cr, Mn

  • Moderate levels of 15 other metals including Pb, Hg, As, and Li


The problem1

The Problem

  • Why?

  • Slag wastes used as fill

  • Other harmful waste also used as fill

    • Fly ash

    • Solid industrial wastes

    • Demolition debris

    • Household trash

  • 600 m3 of fill dumped on 150 km2


Other sources of contamination

Other Sources of Contamination

  • Leakage from Landfills

  • Spills at hazardous waste-handling facilities

  • Road-salt runoff

  • Illegal dumping


Sampling site

Sampling Site

  • Former wetlands filled with steel slag.

  • Water was sampled from an isolated pond fed by diffuse ground water.

  • Land surrounding the site is unvegetated and had never been developed


Sample collection

Sample Collection

  • Samples of precipitated calcite and slag were taken

  • Water was collected in the field using a pump and a .45 micron high-capacity filter


Chemical analysis slag

Chemical Analysis - Slag

  • Composed of Iron slag & Steel slag

    • Iron slag

      • Ca2MgSi2O7

      • Contains little or no iron

      • Uniform in composition

    • Steel slag

      • Composed of 50% calcium silicates

        • Rakinaite Ca3Si2O7

        • Larnite Ca2SiO4


Weathered products

Weathered Products

  • Weathered down to:

    • Rakinaite Ca3Si2O7 + 7H2O → 3Ca2+ + 2H4SiO4 + 6OH-

    • Larnite Ca2SiO4 + 4H2O → 2Ca2+ + H4SiO4 + 4OH-

    • Akermanite Ca2MgSi2O7 + 7H2O → 2Ca2+ + Mg2+ + 2H4SiO4 + 6OH-


Weathered products1

Weathered Products

  • Each reaction releases calcium ions and uses protons

  • Creates Ca-OH in the ground water

  • This explains the high alkalinity of the water


Calcium and carbon dioxide

Calcium and Carbon Dioxide

  • Carbonate from rainwater and underlying sands and soils forms CO32-

  • CO32- is the dominate species at a pH of 10

  • When the alkaline water is exposed to atmospheric CO2 the pH is reduced by 4 factors and calcite precipitates


Calcite reactions

Calcite Reactions

  • At high pH

    • CO2 + H2O→2H+ + CO32-

    • Ca2+ + CO32-→CaCO3

  • At neutral pH

    • H+ + CaCO3 → Ca2+ + HCO3-


Geochemical model

Geochemical Model

  • TITLE Before sparging

  • SOLUTION 1

  • pH 11.2 charge

  • temp 14.5

  • pe 4.075

  • units mmol/L

  • Al .012

  • Ba .00023

  • B .0037

  • Cd .00014

  • Ca .82

  • C .33 as CO3-2

  • Cl .093

  • Cu .00052

  • F .053

  • Fe .00016

  • Pb .00036

  • Li .0049

  • Mg .005

  • Mn .00005

  • N .047 as N03-

  • K .69

  • Si .061

  • Na .57

  • Sr .0015

  • S .14 as SO4-2

  • Zn .0089

  • END

  • TITLE After sparging

  • SOLUTION 1

  • pH 11.2 charge

  • temp 14.5

  • pe 4.075

  • units mmol/L

  • Al .012

  • Ba .00023

  • B .0037

  • Cd .00014

  • Ca .82

  • C .33 as CO3-2

  • Cl .093

  • Cu .00052

  • F .053

  • Fe .00016

  • Pb .00036

  • Li .0049

  • Mg .005

  • Mn .00005

  • N .047 as N03-

  • K .69

  • Si .061

  • Na .57

  • Sr .0015

  • S .14 as SO4-2

  • Zn .0089

  • EQUILIBRIUM_PHASES 1

  • O2(g) -0.670976998

  • CO2(g) -3.5

  • END


Geochemical model1

Geochemical Model

  • ----------------------------After----------------------------

  • pH = 8.587

  • pe = 12.965

  • Specific Conductance (uS/cm, 14 oC) = 226

  • Density (g/cm3) = 0.99937

  • Activity of water = 1.000

  • Ionic strength = 3.779e-003

  • Mass of water (kg) = 1.000e+000

  • Total alkalinity (eq/kg) = 2.502e-003

  • Total CO2 (mol/kg) = 2.385e-003

  • Temperature (deg C) = 14.500

  • Electrical balance (eq) = -7.321e-015

  • Percent error, 100*(Cat-|An|)/(Cat+|An|) = -0.00

  • Iterations = 14

  • Total H = 1.110145e+002

  • Total O = 5.551475e+001

  • ----------------------------Before------------------------

  • pH = 11.573

  • pe = 4.075

  • Specific Conductance (uS/cm, 14 oC) = 410

  • Density (g/cm3) = 0.99930

  • Activity of water = 1.000

  • Ionic strength = 3.630e-003

  • Mass of water (kg) = 1.000e+000

  • Total alkalinity (eq/kg) = 2.549e-003

  • Total CO2 (mol/kg) = 3.300e-004

  • Temperature (deg C) = 14.500

  • Electrical balance (eq) = -7.323e-015

  • Percent error, 100*(Cat-|An|)/(Cat+|An|) = -0.00

  • Iterations = 9

  • Total H = 1.110145e+002

  • Total O = 5.550986e+001


Geochemical model2

Geochemical Model

  • ------------------------------Sample---------------------------

  • Phase SI log IAP log KT

  • Calcite 1.34 -7.09 -8.43 CaCO3

  • CO2(g) -8.76 -10.09 -1.33 CO2

  • Dolomite 0.34 -16.49 -16.84 CaMg(CO3)2

  • Fe(OH)3(a) -0.84 4.05 4.89 Fe(OH)3

  • FeS(ppt) -111.47 -115.38 -3.92 FeS

  • O2(g) -24.29 -27.09 -2.81 O2

  • Pb(OH)2 1.14 9.66 8.52 Pb(OH)2

  • Zn(OH)2(e) -0.02 11.48 11.50 Zn(OH)2

  • ------------------------------Sample after sparging------------

  • Phase SI log IAP log KT

  • Calcite 0.69 -7.74 -8.43 CaCO3

  • CO2(g) -3.50 -4.83 -1.33 CO2

  • Dolomite -0.86 -17.69 -16.84 CaMg(CO3)2

  • Fe(OH)3(a) 1.43 6.32 4.89 Fe(OH)3

  • FeS(ppt) -156.37 -160.28 -3.92 FeS

  • O2(g) -0.67 -3.48 -2.81 O2

  • Pb(OH)2 -0.57 7.96 8.52 Pb(OH)2

  • Zn(OH)2(e) -0.55 10.95 11.50 Zn(OH)2


Possible solutions

As an experimental solution atmospheric air was bubbled through 900 mL of site water that contained 100 g of precipitate.

The water was sparged with a glass gas dispersion tube at a constant rate until pH stabilized

Mortality rate went from 100% in the extremely alkaline water to <10%

Possible Solutions


Possible solutions1

Alternatives:

Sparge the water with 1 atm of CO2

Mix a strong acid like HCl with the water

Pros:

Drops the pH 100 times faster than with atmospheric air

Any additional CO32- or HCl beyond 7 would dissolve the calcite and not affect the pH

Cons:

Those systems can be expensive and labor intensive to set up and monitor

Reduced pH does not necessarily mean more livable.

The toxicity rates were four times higher than in air-sparging

Due to the release of metals as the calcite dissolved

Possible Solutions


My solution

My Solution

  • Add pyrite to the slag fill and through the following reaction it will make the water more acidic

  • 2 FeS2 (s) + 7 O2 + 2 H2O → 2 Fe2+ (aq) + 4 SO4 (aq) + 4 H+

  • Need .3022 g of FeS2 to neutralize 1 L of sample water


When modeled

TITLE Addition of pyrite

SOLUTION 1

pH 11.2 charge

temp 14.5

pe .25

units mmol/L

Al .012

Ba .00023

B .0037

Cd .00014

Ca .82

C .33 as CO3-2

Cl .093

Cu .00052

F .053

Fe .00016

Pb .00036

Li .0049

Mg .005

Mn .00005

N .015 as NH4+

O(0) .55

K .69

Si .061

Na .57

Sr .0015

S 1.26 as SO4-2

Zn .0089

END

TITLE Addition of atmospheric air

SOLUTION 1

pH 11.2 charge

temp 14.5

pe 4.075

units mmol/L

Al .012

Ba .00023

B .0037

Cd .00014

Ca .82

C .33 as CO3-2

Cl .093

Cu .00052

F .053

Fe .00016

Pb .00036

Li .0049

Mg .005

Mn .00005

N .047 as N03-

K .69

Si .061

Na .57

Sr .0015

S .14 as SO4-2

Zn .0089

EQUILIBRIUM_PHASES 1

O2(g) -0.670976998

CO2(g) -3.5

END

When Modeled


Modeling results

Modeling Results

Their Results

My Results

  • ----------------------------Sparging with Air---------------------------

  • pH = 8.587

  • pe = 12.965

  • Specific Conductance (uS/cm, 14 oC) = 226

  • Density (g/cm3) = 0.99937

  • Activity of water = 1.000

  • Ionic strength = 3.779e-003

  • Mass of water (kg) = 1.000e+000

  • Total alkalinity (eq/kg) = 2.502e-003

  • Total CO2 (mol/kg) = 2.385e-003

  • Temperature (deg C) = 14.500

  • Electrical balance (eq) = -7.321e-015

  • Percent error, 100*(Cat-|An|)/(Cat+|An|) = -0.00

  • Iterations = 14

  • Total H = 1.110145e+002

  • Total O = 5.551475e+001

  • ----------------------------Addition of Pyrite---------------------------

  • pH = 7.074

  • pe = 0.250

  • Specific Conductance (uS/cm, 14 oC) = 263

  • Density (g/cm3) = 0.99938

  • Activity of water = 1.000

  • Ionic strength = 4.666e-003

  • Mass of water (kg) = 1.000e+000

  • Total alkalinity (eq/kg) = 3.082e-004

  • Total CO2 (mol/kg) = 3.301e-004

  • Temperature (deg C) = 14.500

  • Electrical balance (eq) = 3.705e-018

  • Percent error, 100*(Cat-|An|)/(Cat+|An|) = 0.00

  • Iterations = 16

  • Total H = 1.110130e+002

  • Total O = 5.551303e+001


Geochemistry of extremely alkaline ph 12 ground water in slag fill aquifers

------------------------------ Addition of Pyrite- ------------------------------

Phase SI log IAP log KT

Alunite 4.31 4.26 -0.06 KAl3(SO4)2(OH)6

Calcite -1.79 -10.22 -8.43 CaCO3

Fe(OH)3(a) -3.67 1.23 4.89 Fe(OH)3

Melanterite -7.68 -10.02 -2.35 FeSO4:7H2O

Pyrite -40.46 -59.24 -18.78 FeS2

Smithsonite -2.32 -12.21 -9.88 ZnCO3

Strontianite -3.68 -12.95 -9.28 SrCO3

Zn(OH)2(e) -2.60 8.90 11.50 Zn(OH)2

------------------------------ Sparging with Air- ------------------------------

Phase SI log IAP log KT

Alunite -6.11 -6.16 -0.06 KAl3(SO4)2(OH)6

Calcite 0.69 -7.74 -8.43 CaCO3

Fe(OH)3(a) 1.43 6.32 4.89 Fe(OH)3

Melanterite -20.78 -23.13 -2.35 FeSO4:7H2OPyrite -256.73 -275.51 -18.78 FeS2

Smithsonite -0.86 -10.74 -9.88 ZnCO3

Strontianite -1.19 -10.47 -9.28 SrCO3

Zn(OH)2(e) -0.55 10.95 11.50 Zn(OH)2


Problems with my modeling

Problems with my modeling

  • Could not make it work if I added the aqueous Fe I would need to.

  • Doesn’t specify how much FeS2 should be added to the soil .

  • A pH –below 8.1 may have dissolved some calcite and brought more heavy metals into solution.


Citations

Citations

  • Roadcap, S. G., Walton, R. K., Bethke, M. C. (2005). Geochemistry of extremely alkaline (pH > 12) ground water    in slag-fill aquifers Ground Water, 43 (6), 806-816.


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