Oxidizing Pyrite 1.FeS 2 + 3.5 O 2 + H 2 O  Fe 2+ + 2 SO 4 2- + 2 H + 2.FeS 2 + 14 Fe 3+ + 8 H 2 O  15 Fe 2+ + 2 SO 4 2- + 16 H + 3.14Fe 2+ + 3.5 O 2.

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Oxidizing Pyrite 1.FeS O 2 + H 2 O  Fe SO H + 2.FeS Fe H 2 O  15 Fe SO H Fe O H +  14 Fe H 2 O Reaction 3 is SLOW at low pH  Traditional view of microbial activity describes how microbes speed that reaction up!

Oxidizing Pyrite FeS O 2 + H 2 O  Fe SO H + FeS Fe H 2 O  15 Fe SO H + The oxidation of FeS 2 transfers 14 electrons from S 2 2- to 2 SO 4 2- !! These reactions occur over many steps to develop pathways of oxidation

speciespK 1 pK 2 H2SH2S H2S2O3H2S2O H2S4O6H2S4O6 -2 H 2 SO H 2 SO Data from Williamson and Rimstidt, 1992; Schoonen and Barnes, 1988

Oxidation Kinetics and Microbes Do microbes couple sulfur oxidation to O 2 /Fe 3+ reduction or is Fe 3+ oxidation of those species faster and microbes can only gain energy from Fe 2+ oxidation?

Field Site: Iron Mountain Northern CA Iron Mountain = Opportunity to study FeS 2 oxidation inside a giant block of FeS 2 !

Iron Mountain Mine Complex large complex of several mines operated intermittently between the 1860’s and 1962 for Au, Ag, Cu, and Zn Became a superfund site in 1983 – millions spent on treatment of effluent Site of lowest recorded ‘natural’ pH= -3.6 (Nordstrom et al., 2000)

pH of majority of the flow Fe T is ~ 0.2 – 0.4 M, SO 4 2- is ~0.6 – 1.1 M An average of 100,000 moles FeS 2 /day is oxidized (range ~ 20, ,000 mol/day) –~2 m 3 block weighing about a ton per day –Requires 350,000 mol O 2 = ~ 8,000 m 3 O 2 FeS 2 oxidation requires: 30 g/l in water (O 2 saturation ~ 3 mg/l) Water must be re-oxidized thousands of times before exiting, about once per cm. Effluent Geochemistry

Life at pH 0-1 and lower?? Significant communities of bacteria, archaea, fungi, and protists!!

Microbes and FeS 2 oxidation S S S Fe aerobic anaerobic

Iron Mountain Microbial Metabolisms Organism##Org C/ O 2 Org C /Fe 3+ Fe 2+ /O 2 S x O y n- /O 2 S x O y n- /Fe 3+ Ferromicrobium sp. Acidimicrobium sp. Few Yes Sulfobacillus spp. Few Yes Thermoplasma sp. Few YesNo Fungi, protists Some YesNo Ferroplasma acidarmanus Lots Yes No Leptospirillum spp. Lots No YesNo

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Tetrathionate had previously been assumed to assumed to oxidize very quickly when formed as a product of pyrite oxidation (Kelsall, 1999; Moses et al., 1987; D.K.K. Nordstrom, personal communication). Results of kinetic experiments show that this assumption has been in error and that the oxidation kinetics of tetrathionate in acidic solutions with ferric iron is quite slow, defined by the rate law at 70º C and pH 1.5: r = ±0.3 [S 4 O 6 2- ] 0.3±0.08 [Fe 3+ ] 0.06±0.07 where r is in units of mol L -1 sec -1. The apparent activation energy (EA) for tetrathionate oxidation at pH 1.5 is 105 ± 4 KJ/mol.

Contrary Creek, VA FeS (aq) molecular clusters found as a significant potential substrate for Fe 2+ oxidizing microbes Profile – Contrary Creek wetland

Competition between microbes and abiotic processes Neutrophilic Iron Oxidizers – cultures of ES-1  what controls the environments where they can eke out a living??

Abiotic-Biotic kinetics