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) 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 Problem Why? Slag wastes used as fill Other harmful waste also used as fill –Fly ash –Solid industrial wastes –Demolition debris –Household trash 600 m 3 of fill dumped on 150 km 2

Other Sources of Contamination Leakage from Landfills Spills at hazardous waste-handling facilities Road-salt runoff Illegal dumping

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 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 Composed of Iron slag & Steel slag –Iron slag Ca 2 MgSi 2 O 7 Contains little or no iron Uniform in composition –Steel slag Composed of 50% calcium silicates  Rakinaite Ca 3 Si 2 O 7  Larnite Ca 2 SiO 4

Weathered Products Weathered down to: –Rakinaite Ca 3 Si 2 O 7 + 7H 2 O → 3Ca H 4 SiO 4 + 6OH - –Larnite Ca 2 SiO 4 + 4H 2 O → 2Ca 2+ + H 4 SiO 4 + 4OH - –Akermanite Ca 2 MgSi 2 O 7 + 7H 2 O → 2Ca 2+ + Mg H 4 SiO 4 + 6OH -

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 Carbonate from rainwater and underlying sands and soils forms CO 3 2- CO 3 2- is the dominate species at a pH of 10 When the alkaline water is exposed to atmospheric CO 2 the pH is reduced by 4 factors and calcite precipitates

Calcite Reactions At high pH –CO 2 + H 2 O→2H + + CO 3 2- –Ca 2+ + CO 3 2- →CaCO 3 At neutral pH – H + + CaCO3 → Ca 2+ + HCO3 -

Geochemical Model TITLE After sparging SOLUTION 1 pH 11.2 charge temp 14.5 pe units mmol/L Al.012 Ba B.0037 Cd Ca.82 C.33 as CO3-2 Cl.093 Cu F.053 Fe Pb Li.0049 Mg.005 Mn N.047 as N03- K.69 Si.061 Na.57 Sr.0015 S.14 as SO4-2 Zn.0089 EQUILIBRIUM_PHASES 1 O2(g) CO2(g) -3.5 END TITLE Before sparging SOLUTION 1 pH 11.2 charge temp 14.5 pe units mmol/L Al.012 Ba B.0037 Cd Ca.82 C.33 as CO3-2 Cl.093 Cu F.053 Fe Pb Li.0049 Mg.005 Mn N.047 as N03- K.69 Si.061 Na.57 Sr.0015 S.14 as SO4-2 Zn.0089 END

Geochemical Model After pH = pe = Specific Conductance (uS/cm, 14 oC) = 226 Density (g/cm3) = Activity of water = 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) = Electrical balance (eq) = e-015 Percent error, 100*(Cat-|An|)/(Cat+|An|) = Iterations = 14 Total H = e+002 Total O = e Before pH = pe = Specific Conductance (uS/cm, 14 oC) = 410 Density (g/cm3) = Activity of water = 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) = Electrical balance (eq) = e-015 Percent error, 100*(Cat-|An|)/(Cat+|An|) = Iterations = 9 Total H = e+002 Total O = e+001

Geochemical Model Sample Phase SI log IAP log KT Calcite CaCO3 CO2(g) CO2 Dolomite CaMg(CO3)2 Fe(OH)3(a) Fe(OH)3 FeS(ppt) FeS O2(g) O2 Pb(OH) Pb(OH)2 Zn(OH)2(e) Zn(OH) Sample after sparging Phase SI log IAP log KT Calcite CaCO3 CO2(g) CO2 Dolomite CaMg(CO3)2 Fe(OH)3(a) Fe(OH)3 FeS(ppt) FeS O2(g) O2 Pb(OH) Pb(OH)2 Zn(OH)2(e) 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 Alternatives: –Sparge the water with 1 atm of CO 2 –Mix a strong acid like HCl with the water –Pros: Drops the pH 100 times faster than with atmospheric air Any additional CO 3 2- 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

My Solution Add pyrite to the slag fill and through the following reaction it will make the water more acidic 2 FeS 2 (s) + 7 O H 2 O → 2 Fe 2+ (aq) + 4 SO 4 (aq) + 4 H + Need.3022 g of FeS 2 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 B.0037 Cd Ca.82 C.33 as CO3-2 Cl.093 Cu F.053 Fe Pb Li.0049 Mg.005 Mn 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 units mmol/L Al.012 Ba B.0037 Cd Ca.82 C.33 as CO3-2 Cl.093 Cu F.053 Fe Pb Li.0049 Mg.005 Mn N.047 as N03- K.69 Si.061 Na.57 Sr.0015 S.14 as SO4-2 Zn.0089 EQUILIBRIUM_PHASES 1 O2(g) CO2(g) -3.5 END

Modeling Results Sparging with Air pH = pe = Specific Conductance (uS/cm, 14 oC) = 226 Density (g/cm3) = Activity of water = 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) = Electrical balance (eq) = e-015 Percent error, 100*(Cat-|An|)/(Cat+|An|) = Iterations = 14 Total H = e+002 Total O = e Addition of Pyrite pH = pe = Specific Conductance (uS/cm, 14 oC) = 263 Density (g/cm3) = Activity of water = 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) = Electrical balance (eq) = 3.705e-018 Percent error, 100*(Cat-|An|)/(Cat+|An|) = 0.00 Iterations = 16 Total H = e+002 Total O = e+001 Their Results My Results

Addition of Pyrite Phase SI log IAP log KT Alunite KAl3(SO4)2(OH)6 Calcite CaCO3 Fe(OH)3(a) Fe(OH)3 Melanterite FeSO4:7H2O Pyrite FeS2 Smithsonite ZnCO3 Strontianite SrCO3 Zn(OH)2(e) Zn(OH) Sparging with Air Phase SI log IAP log KT Alunite KAl3(SO4)2(OH)6 Calcite CaCO3 Fe(OH)3(a) Fe(OH)3 Melanterite FeSO4:7H2O Pyrite FeS2 Smithsonite ZnCO3 Strontianite SrCO3 Zn(OH)2(e) Zn(OH)2

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 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),