Sulfide oxidation experiments on pyrite, galena, and sphalerite

combined with isotope measurements

Tichomirowa (DFG TI 19-1 , -2, -3) 29.03.2017

HAUBRICH & TICHOMIROWA (2002)

Motivation

Sulfide oxidation: release of dissolved ions/elements: sulfate, Fe, Zn, Pb, As, Cd… How and where occurs sulfide oxidation (rates)? Rate limiting steps?

Himmelfahrt mine: Solution (oxidation of sulfides) and precipitation (illite, jarosite, anglesite, iron-(oxy)hydrides) – What ions/elements remain in the mine and how?

Oxidation of pyrite: by O2 : FeS2 + 7/2O2 + H2O → 2SO4

2- + Fe2+ + 2H+ by Fe3+ : FeS2 + 14Fe3+ + 8H2O → 2SO4

2- + 15Fe2+ + 16H+ Fe2+ + 1/4O2 + H+ → ½H2O + Fe3+

Why isotopes? = fingerprint

Polymetallic mine „Himmelfahrt-Fundgrube“ Freiberg, Germany

Haubrich & Tichomirowa (2002): SULFUR AND OXYGEN ISOTOPE GEOCHEMISTRY OF ACID MINE DRAINAGE – THE POLYMETALLIC SULFIDE DEPOSIT ‘‘HIMMELFAHRT FUNDGRUBE’’ IN FREIBERG (GERMANY). Isotopes Environ. Health Stud., 2002, Vol. 38(2), pp. 121–138.

3. Level

1. Level

ore lode

2. Level

Tichomirowa (DFG TI 19-1 , -2, -3)

Best understood: Pyrite (FeS2) oxidation

If no Fe3+: oxidation starts only if O2 is available If no Fe3+: oxidation starts only if O2 is available; O2 adsorbs on pyrite grains – grain size of pyrite is very important (Tichomirowa & Junghans, 2009)

If no Fe3+: oxidation starts only if O2 is available; O2 adsorbs on pyrite grains – grain size of pyrite is very important (Tichomirowa & Junghans, 2009)

After 100 days oxidation 80-90% oxygen in sulfate stems from the water molecule (Heidel et al., 2009)

Heidel & Tichomirowa (DFG TI 19-1 , -2, -3)

Best understood: Pyrite oxidation

If no Fe3+: oxidation starts only if O2 is available; O2 adsorbs on pyrite grains – grain size of pyrite is very important (Tichomirowa & Junghans, 2009)

After 100 days oxidation 80-90% oxygen in sulfate stems from the water molecule (Heidel et al., 2009)

But: even after 150 days some O2 (9%) is permanently incorporated into SO4

2-

Heidel & Tichomirowa (2010): The role of dissolved molecular oxygen in abiotic pyrite oxidation under acid pH conditions – Experiments with 18O-enriched molecular oxygen. Appl. Geochemistry 25, 1664-1675

0.5 O2 + 2 H+ + 2 e- H2O SO32- + 0.5 O2 SO4

2-

Heidel & Tichomirowa (2011): The isotopic composition of sulphate from anaerobic and low oxygen pyrite oxidation experiments with ferric iron – New insights into oxidation mechanisms. Chemical Geology 281, 305-316

„anaerobic“: DO (dissolved oxygen) < 0.0005 mmol/L; „low oxygen“: DO = 0.011 mmol/L

Increase of oxidation rate (max = 5 x 10-9 mmol m-2 s-1) with increasing ratio Fe3+/pyrite surface

Fe3+/surface > 3.8 mmol/m2: 100% oxygen in sulphate from water (anaerobic experiments)

Fe3+/surface < 3.8 mmol/m2: >0 – 70% oxygen in sulphate from molecular oxygen (anaerobic)

Fe3+/surface 0.001-0.86 mmol/m2: 20 – 70% oxygen in sulphate from molecular oxygen (low oxygen) Role of molecular oxygen!

Heidel & Tichomirowa (2011): The isotopic composition of sulphate from anaerobic and low oxygen pyrite oxidation experiments with ferric iron – New insights into oxidation mechanisms. Chemical Geology 281, 305-316

Oxidation by Fe3+: fractionation of δ34S (ca. -1‰); formation of elemental S Oxidation by O2: no fractionation of δ34S

Pyrite oxidation Role of dissolved oxygen (DO): • Initial adsorption on pyrite surface to start oxidation: pyrite grain size! • At low Fe3+/pyrite surface (natural conditions): 20-70% DO in final sulphate • Some DO incorporated into water: 0.5 O2 + 2 H+ + 2 e- H2O

Role of water: • Without Fe3+ oxidation (by DO): after 100 days ca. 90% oxygen of sulphate derived from water • Anaerobic conditions: only at high Fe3+ (Fe3+/surface >3.8 mmol/m2) all oxygen in sulphate derived from water

Sulphur isotopes; fractionation (-1‰) only if oxidation by Fe3+

(due to formation of elemental S)

Absence/minor amounts of intermediate S-species (elemental S?)

Heidel & Tichomirowa (2011): Galena oxidation investigations on oxygen and sulphur isotopes. Isotopes in Environmental and Health Studies; Vol. 47, No. 2, 169–188

Galena (PbS) oxidation

much slower than pyrite oxidation; Pyrite (DO+H2O): 6 x 10-11 to 2 x 10-10 mmol m-2 s-1

Pyrite (Fe3+): 10-9 to 10-7 mmol m-2 s-1

Galena (DO+H2O): 10-10 – 10-12 mmol m-2 s-1, fastest during first 10 days. pH evolves towards 4 – 5 No faster dissolution with lower grain sizes Different dissolution mechanisms:

• pH =2: „non-oxidative dissolution“ very low sulphate production but release of Pb (and Fe) into solutions after 10 days no increase of concentrations no isotope measurements because of low sulphate • pH = 6, 8: „oxidative dissolution“ higher sulphate concentrations (but lower Pb, no Fe) in solution; thiosulfate (S2O3

2-) < SO42- concentrations

traces of sulphite ca. 75% oxygen in sulphate from water fractionation of S isotopes (anglesite formation)

Heidel & Tichomirowa (2011): Galena oxidation investigations on oxygen and sulphur isotopes. Isotopes in Environmental and Health Studies; Vol. 47, No. 2, 169–188

Galena Oxidation: • much slower • many intermediate sulfur species • passivation products like angesite (PbSO4) • Oxidation not faster with Fe3+

Sphalerite (ZnS) oxidation ZnS + 2 O2 Zn2+ + SO4

2- ZnS + 8 Fe3+ + 4 H2O Zn2+ + 8 Fe2+ + SO4

2- + 8 H+

Heidel et al. (2011): Sphalerite oxidation pathways detected by oxygen and sulphur isotope studies . Applied Geochemistry 26, 2247–2259.

H2S

much slower than pyrite oxidation; Pyrite (DO+H2O): 6 x 10-11 to 2 x 10-10 mmol m-2 s-1

Pyrite (Fe3+): 10-9 to 10-7 mmol m-2 s-1

sphalerite (DO+H2O): 10-10 – 10-12 mmol m-2 s-1, fastest during first 2-5 days. pH evolves towards 7 (= proton consumption!)

Different dissolution mechanisms: • pH =2: „non-oxidative dissolution“ very low sulphate production but release of Zn and Fe into solutions (first 5 days) loss of H2S • pH = 6 (also pH 2 after 5 days) sharp decrease in reaction rate after 2-5 days up to day 20: all oxygen in sulphate derived from DO (reaction 1) from day 50-100: more and more oxygen in sulphate produced by Fe3+ (dissolved

from sphalerite) = reaction 2

Sphalerite Oxidation: • much slower • many intermediate sulfur species (polysulfides and thiosulfates) • passivation products like polysulfides, Zn deficit due to adsorption to ferric oxyhydroxides)

Heidel et al. (2011): Sphalerite oxidation pathways detected by oxygen and sulphur isotope studies . Applied Geochemistry 26, 2247–2259.

Heidel et al. (2013): Oxygen and sulfur isotope investigations of the oxidation of sulfide mixtures containing pyrite, galena, and sphalerite. Chemical Geology 342, 29–43.

Heidel et al. (2013): Oxygen and sulfur isotope investigations of the oxidation of sulfide mixtures containing pyrite, galena, and sphalerite. Chemical Geology 342, 29–43.

Ga

Sph Py

Pb+S

After 3 years

• preferential oxidation of galena and sphalerite (over pyrite) • first 30 days: oxidation mainly by O2 • afterwards oxidation mainly by Fe3+

• formation of inter- mediate soluble S species (thiosulfates, sulfite) • formation of anglesite (Pb+S) • in difference to single Sphal- and Ga -experiments: no sharp decrease of reaction rate • complex behaviour of isotopes: different fractionation and isotope exchange processes (sulphite-water) in addition to varying chemical processes

Heidel et al. (2013): Oxygen and sulfur isotope investigations of the oxidation of sulfide mixtures containing pyrite, galena, and sphalerite. Chemical Geology 342, 29–43.

back to nature…

Probenteilung Zugabe von destilliertem Wasser (100 bzw. 400 ml): Bestimmung von pH, Eh,

Leitfähigkeit

TICHOMIROWA, M.; PELKNER, S.; JUNGHANS, M.; HAUBRICH, F. (2003): Sulfide oxidation in acid mine drainage: relationship between precipitated and dissolved sulfates at the polymetallic sulfide deposit Freiberg (Germany) and consequences for mobilisation of heavy metals. In: Schulz H.D., Hadeler A. (Eds.): Geochemical processes in soil and groundwater WILEY-VCH GmbH & Co., 356-379.

Jarosit auf Galenit

TICHOMIROWA, M.; PELKNER, S.; JUNGHANS, M.; HAUBRICH, F. (2003): Sulfide oxidation in acid mine drainage: relationship between precipitated and dissolved sulfates at the polymetallic sulfide deposit Freiberg (Germany) and consequences for mobilisation of heavy metals. In: Schulz H.D., Hadeler A. (Eds.): Geochemical processes in soil and groundwater WILEY-VCH GmbH & Co., 356-379.

(K, Na, H3O, Pb) Fe3 (SO4)2 (OH)6

Tichomirowa (2016): Fingerabdrücke und versteinerte Uhren – Isotope als Detektive in der Forschung. ACAMONTA 23, 25-26.

Tichomirowa & Heidel (2012): Regional and temporal variability of the isotope composition (O, S) of atmospheric sulphate in the region of Freiberg, Germany, and consequences for dissolved sulphate in groundwater and river water. Isotopes in Environmental and Health Studies Vol. 48, 118–143

Tichomirowa & Heidel (2012): Regional and temporal variability of the isotope composition (O, S) of atmospheric sulphate in the region of Freiberg, Germany, and consequences for dissolved sulphate in groundwater and river water. Isotopes in Environmental and Health Studies Vol. 48, 118–143

less than one year (10 month): sulphate from precipitation through mine into river NOT 100 YEARS

Summary: Oxidation experiments

Role of O2: for intializing the oxidation: - initial sorption on pyrite grains (grain size) - initial oxidation on ZnS, PbS and sulfide mixes - later as an electron acceptor

Role of intermediate S species and anglesite (PbS, ZnS, and sulfide mix): - fractionation of S- and O-isotopes (complex) - passivation of surface (anglesite, jarosite) - preferential oxidation of PbS and ZnS (to FeS2) results in much slower oxidation rates than single pyrite oxidation

Very slow oxidation of single PbS and ZnS, - increase of pH - stop after a few days

Summary: Himmelfahrt Fundgrube

flooded area (500 m depth): - fixation of Fe3+ (oxyhydrides, jarosite) - consumption of O2: very low DO in flooded water until 2002, stratified water column

aerated area above Rotschönberger Stolln (200 m): - sphalerite already mainly dissolved - galena surface passivated by anglesite - today mainly oxidation of pyrite (acid pH) - „Letten“: jarosite + illite (fixation of Pb) - upper 100 m already oxidised, another 100 m left for oxidation - decreasing sulphate from industrial source - decreasing sulphate from soil (formerbrown coal combustion)

References: HAUBRICH, F.; TICHOMIROWA, M. (2002): Sulfur and oxygen isotope geochemistry of acid mine drainage – the polymetallic sulfide deposit „Himmelfahrt Fundgrube“ in Freiberg (Germany). Isotopes in Environmental and Health Studies, 38 (2), 121 – 138. TICHOMIROWA, M.; PELKNER, S.; JUNGHANS, M.; HAUBRICH, F. (2003): Sulfide oxidation in acid mine drainage: relationship between precipitated and dissolved sulfates at the polymetallic sulfide deposit Freiberg (Germany) and consequences for mobilisation of heavy metals. In: Schulz H.D., Hadeler A. (Eds.): Geochemical processes in soil and groundwater WILEY-VCH GmbH & Co., 356-379. HEIDEL C.; TICHOMIROWA, M.; MATSCHULLAT, J. (2007): Lead and strontium isotopes as indicators for mixing processes of water in the former mine "Himmelfahrt Fundgrube", Freiberg (Germany). Isotopes in Environment and Health Studies, 43, 339-354. TICHOMIROWA, M.; HAUBRICH, F.; KLEMM, W.; MATSCHULLAT, J. (2007): Regional and temporal (1992-2004) evolution of air-borne sulphur isotope composition in Saxony, southeastern Germany, central Europe. Isotopes in Environment and Health Studies, 43, 295-305. HEIDEL C., TICHOMIROWA M., JUNGHANS M. (2009): The influence of pyrite grain size on the final oxygen isotope difference between sulphate and water in aerobic pyrite oxidation experiments. Isotopes in Environmental and Health Studies 45, 1-22. JUNGHANS M., TICHOMIROWA M. (2009): Using sulfur and oxygen isotope data for sulfide oxidation assessment in the Freiberg polymetallic sulfide mine. Applied Geochemistry 24, 2034-2050. TICHOMIROWA, M., JUNGHANS, M. (2009): Oxygen isotope evidence for sorption of molecular oxygen to pyrite surfaces and incorporation into sulfate in oxidation experiments. Applied Geochemistry 24, 2072-2092.

HEIDEL C., TICHOMIROWA M. (2010): The role of dissolved molecular oxygen in abiotic pyrite oxidation under acid pH conditions - experiments with 18O-enriched molecular oxygen. Appl. Geochem. 25, 1664-1675 TICHOMIROWA M., HEIDEL C., JUNGHANS M., HAUBRICH F., MATSCHULLAT J. (2010): Sulfate and strontium source identification in water by O, S, Sr isotopes and their temporal changes (1997-2008) in the region of Freiberg, central-eastern Germany. Chem. Geol. 276, 104-118. Heidel C., Tichomirowa M. (2011): Galena oxidation investigations on oxygen and sulphur isotopes. Isotopes in Environm. Health Studies 47, 169-188. HEIDEL C., TICHOMIROWA M., BREITKOPF C. (2011): Sphalerite oxidation pathways detected by oxygen and sulfur isotope studies. Appl. Geochem. 26, 2247-2259. Heidel C., Tichomirowa M. (2011): The isotopic composition of sulfate from anaerobic and low oxygen pyrite oxidation experiments with ferric iron – New insights into oxidation mechanisms. Chem. Geol. 281, 305-316. TICHOMIROWA M., HEIDEL C. (2012): Regional and temporal variability of the isotope composition (O, S) of atmospheric sulphate in the region of Freiberg, Germany, and consequences for dissolved sulphate in groundwater and river water. Isotopes in Environm. Health Studies 48, 118-143. HEIDEL C., TICHOMIROWA M., JUNGHANS M. (2013): Oxygen and sulfur isotope investigations of the oxidation of sulfide mixtures containing pyrite, galena and sphalerite. Chem. Geol. 342, 29-43. TICHOMIROWA M (2016): Fingerabdrücke und versteinerte Uhren – Isotope als Detektive in der Forschung. ACAMONTA 23, 24-25.