1 / 23

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

ebony
Télécharger la présentation

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

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Geochemistry of Extremely Alkaline (pH > 12) Ground water in Slag–Fill Aquifers By Austin Krabbenhoft 11/29/10

  2. Lake Calumet - Chicago

  3. 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

  4. 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

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

  6. 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

  7. 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

  8. 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

  9. Weathered Products • Weathered down to: • Rakinaite Ca3Si2O7 + 7H2O → 3Ca2+ + 2H4SiO4 + 6OH- • Larnite Ca2SiO4 + 4H2O → 2Ca2+ + H4SiO4 + 4OH- • Akermanite Ca2MgSi2O7 + 7H2O → 2Ca2+ + Mg2+ + 2H4SiO4 + 6OH-

  10. 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

  11. 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

  12. Calcite Reactions • At high pH • CO2 + H2O→2H+ + CO32- • Ca2+ + CO32-→CaCO3 • At neutral pH • H+ + CaCO3 → Ca2+ + HCO3-

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. ------------------------------ 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 FeSO4:7H2O Pyrite -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

  22. 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.

  23. 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.

More Related