Impact of Iron-Reducing Bacteria on the Corrosion ... - ACS Publications

May 19, 2015 - CEA, DEN, DTN/SMTA/LMTE, 13108 Saint Paul lez Durance, France. ‡. CEA, DEN, DANS/DPC/SEARS/LISL, F91191 Gif-sur-Yvette, France...
0 downloads 0 Views 4MB Size
Subscriber access provided by NEW YORK UNIV

Article

Impact of iron-reducing bacteria on the corrosion rate of carbon steel under simulated geological disposal conditions Marta K. Schütz, Michel L. Schlegel, Marie Libert, and Olivier Bildstein Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b00693 • Publication Date (Web): 19 May 2015 Downloaded from http://pubs.acs.org on May 19, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 35

Environmental Science & Technology

Impact of iron-reducing bacteria on the corrosion rate of carbon steel under simulated geological disposal conditions Marta K. Schütz§,ǁ,¥,†,*, Michel L. Schlegel #,ǂ,¥, Marie Libert §,¥, Olivier Bildstein §,¥ §

CEA, DEN, DTN/SMTA/LMTE, 13108 Saint Paul lez Durance, France

#

CEA, DEN, DANS/DPC/SEARS/LISL, F91191 Gif-sur-Yvette, France

* Corresponding author: [email protected] KEYWORDS: biocorrosion, iron-reducing bacteria, magnetite, hydrogen, carbon steel, corrosion rate, geological disposal 1

ABSTRACT. The current projects for the disposal of high-level radioactive waste rely on

2

underground burial and confinement by metallic envelopes that are susceptible to corrosion

3

processes. The impact of microbial activity must be fully clarified in order to provide biological

4

parameters for predictive reactive transport models. This study investigates the impact of

5

hydrogenotrophic iron-reducing bacteria (Shewanella oneidensis strain MR-1) on the corrosion

6

rate of carbon steel under simulated geological disposal conditions by using a geochemical

7

approach. It was found that corrosion damage changes mostly according to the experimental

8

solution (i.e. chemical composition). Magnetite and vivianite were identified as the main

9

corrosion products. In the presence of bacteria, the corrosion rate increased by a factor 1.3

ACS Paragon Plus Environment

1

Environmental Science & Technology

Page 2 of 35

10

(according to weight loss analysis) to 1.8 (according to H2 measurements) and the detected

11

amount of magnetite diminished. The mechanism likely to enhance corrosion is the

12

destabilization and dissolution of the passivating magnetite layer by reduction of structural Fe(III)

13

coupled to H2 oxidation.

14 15

INTRODUCTION

16

The disposal of high-level radioactive waste (HLW) in deep geological formations is the

17

solution investigated for HLW management in many countries. In these repositories, long-term

18

confinement of HLW would be ensured by a multi-barrier system involving several natural (e.g.

19

clay minerals) and/or engineered barriers (e.g. carbon steel, stainless steel, glass, concrete).1 An

20

assessment of the long-term behavior of the radioactive waste and confining materials in the

21

geological environment is crucial to demonstrate the disposal safety. This assessment entails an

22

understanding of corrosion of the successive metallic barriers in contact with water coming from

23

the geological formation.

24

Corrosion can be described as a process coupling the oxidation of metals (anodic reaction) and

25

the reduction of an oxidizing agent (cathodic reaction) in the presence of an electrolyte. For

26

example, iron corrosion by water under anoxic conditions usually lead to the release of Fe2+

27

which precipitates as Fe(OH)2 according to:

28 29

Fe + 2H2O → Fe2+ + 2OH- + H2 → Fe(OH)2 + H2

(1)

30 31 32

Fe(OH)2 is metastable in solution and oxidizes to form magnetite (Fe3O4).2 The overall chemical reaction describing iron oxidation and magnetite formation can be written:

ACS Paragon Plus Environment

2

Page 3 of 35

Environmental Science & Technology

33 34

3Fe + 4H2O → Fe3O4 + 4H2

(2)

35 36

However, this simple description does not apply in the geological environment, where

37

physicochemical conditions change with time and promote the formation of several distinct solid

38

corrosion products at the metal surface. In addition, these solid products can further protect the

39

metal from corrosion, depending on their chemistry and morphology. The current consensus is

40

that the most aggressive forms of corrosion (e.g. localized, stress corrosion cracking) will occur

41

during initial transient conditions in the repository, and more predictable generalized corrosion

42

will take place later.3 Several studies have suggested that decreasing long-term corrosion rates

43

may result from the presence of a passivating layer made of magnetite in direct contact with the

44

metal surface.4-10 However, changes in the environmental conditions (e.g. pH, redox potential,

45

CO2 pressure, presence of microorganisms) can affect the stability of passivating layers and,

46

therefore, the overall susceptibility of the metal to corrosion.

47

Corrosion associated to the action of microorganisms is known as either microbiologically

48

influenced corrosion (MIC) or biocorrosion. MIC is usually related to the presence of biofilms

49

and to bacterial metabolism11,12 which can control physicochemical properties at the metal

50

surface,13-15 alter the properties and stability of passivating layers,16-18 and eventually modify

51

(increase or decrease) the kinetics of cathodic and/or anodic reactions.19,20 Of specific concern is

52

the role of iron-reducing bacteria (IRB), for which either inhibitory or enhancing effects have

53

been hypothesized.21-24 Indeed, magnetite destabilization and dissolution under anaerobic

54

conditions has been observed as a result of the activity of bacteria using hydrogen (H2) to reduce

55

structural Fe(III).17,18,25 This mechanism is therefore believed to influence the corrosion rate. In

56

fact, corrosion processes can provide all the necessary chemical compounds for IRB anaerobic

ACS Paragon Plus Environment

3

Environmental Science & Technology

Page 4 of 35

57

bioactivity, such as H2 as electron donor and Fe(III) from Fe hydr(oxides) as electron acceptor.

58

Hydrogen is a potent energetic substrate for anaerobic microbial communities, especially in

59

geological formations containing small amounts of biodegradable organic matter.26-30 In addition,

60

the extreme conditions (e.g. radiation, desiccation, high temperature and pressure) that will

61

prevail during the early lifetime of the geological repository should not prevent microbial

62

survival and subsequent growth when conditions will become more favorable: radiation dose rate

63

< 60 Sv.h-1, temperature < 70°C, and water saturation > 0.97.20,31 Therefore, the effect of

64

microbial activity on corrosion needs to be investigated and quantified in the framework of

65

safety assessment of HLW geological disposal. Our previous work demonstrated the impact of

66

hydrogenotrophic IRB on corrosion process by combining geochemical and electrochemical

67

techniques.18 Short term corrosion rates (20 days) were estimated from aqueous Fe concentration

68

(in the case of geochemical measurements) and from exchanged charge (in the case of

69

electrochemical measurements).

70

The objective of the present study is to assess the impact of hydrogenotrophic IRB on carbon

71

steel corrosion mechanisms and corrosion rate on a longer timeframe (5 months) and using

72

additional techniques. Corrosion rates were determined by weight loss analysis and H2

73

measurements in order to compare these two methods. The presence and nature of corrosion

74

products was assessed by spectroscopic and structural techniques to relate the discrepancies in

75

corrosion rate to the nature of corrosion products. Shewanella oneidensis strain MR-1 has been

76

chosen as model organism for this study because it is able not only to oxidize organic matter but

77

also hydrogen, an abundant energy source in such a disposal environment.28

78 79

MATERIALS AND METHODS

ACS Paragon Plus Environment

4

Page 5 of 35

Environmental Science & Technology

80

Experimental solutions. Two experimental solutions with distinct chemical compositions

81

were used in this study: M1 and S1 (see chemical composition in Table 1). M1 is a minimal

82

medium used to cultivate IRB species but with a chemical composition slightly modified in order

83

to be representative of the groundwater from the argillaceous Callovo-Oxfordian formation of

84

the French Underground Research Laboratory (FURL, Bure, France).18,32 For comparison

85

purposes, a solution (S1) with simplified chemical composition was also used. Its composition

86

consists in a mixture of 10 mM Na2SO4, 2 mM NaHCO3, and vitamins (0.08 mM nicotinic acid,

87

0.01 mM thiamine-HCl, 0.40 µM biotine). The sulfate concentration is similar to that measured

88

in the FURL groundwater.32 The pH in the M1 and S1 was adjusted to ~7 with NaOH, and

89

solutions were sterilized by autoclaving (121°C, 20 min), except for the thermolabile

90

components (e.g. vitamins) which were filter-sterilized through a 0.22 µm filter and added to the

91

autoclaved solutions.

92 93

Table 1. Chemical composition of the M1 and S1 solutions. Concentration Compound M1

S1

Na2SO4

-

10 mM

(NH4)2SO4

9 mM

-

Na2SeO4

11 µM

-

HEPES

17 mM

-

NaHCO3

2 mM

2 mM

K2HPO4

0.5 mM

-

KH2PO4

0.3 mM

-

CoSO4.7H2O

5 µM

-

ACS Paragon Plus Environment

5

Environmental Science & Technology

NiSO4.6H2O

5 µM

-

NaCl

10 µM

-

H3BO3

45 µM

-

ZnSO4.7H2O

0.8 µM

-

Na2MoO4.2H2O

3 µM

-

CuSO4.5H2O

0.2 µM

-

MnSO4.H2O

1 µM

-

MgSO4.7H2O

0.8 mM

-

CaCl2.2H2O

0.4 mM

-

FeSO4.7H2O

4 µM

-

arginine

0.11 mM

-

glutamate

0.13 mM

-

serine

0.19 mM

-

nicotinic acid

0.08 mM

0.08 mM

thiamine-HCl

0.01 mM

0.01 mM

biotine

0.40 µM

0.40 µM

Page 6 of 35

94 95

Bacterial culture. Shewanella oneidensis strain MR-1 (ATCC 700550TM) was used as model

96

of hydrogenotrophic IRB in the biotic experiments. Pre-cultures were obtained aerobically at the

97

beginning of stationary growth phase in Luria Bertani Broth (LB) medium (5 g.L-1 NaCl, 10 g.L-

98

1

99

medium by centrifugation (4000 rpm, 20 min), washed once with sterile M1 or S1 solutions and

100

then inoculated into the batch reactors. The initial bacterial concentration was determined by

101

epifluorescence method with LIVE/DEAD® BacLight™ kit33,34, and equalled 108 cells.mL-1.

tryptone, 5 g.L-1 yeast extract) after 24 h at 30°C. Bacterial cells were harvested from the LB

102

Corrosion experiments. One- and 5-months experiments were performed in 250 mL batch

103

reactors at 30oC under anaerobic atmosphere (N2:CO2 ratio of 90:10%) and abiotic (without

ACS Paragon Plus Environment

6

Page 7 of 35

Environmental Science & Technology

104

bacteria) or biotic (with bacteria) conditions. The experimental conditions were detailed in our

105

previous study.18 All experiments were started under aseptic conditions by introducing 140 mL

106

of experimental solution (either M1 or S1) and one cylindrical coupon sample (A37 low carbon

107

steel polished up to 600 grit) into glass reactors without agitation. The coupons were laterally

108

embedded in a diallyl phthalate glass-fiber resin in order to expose only a basal surface of 0.8

109

cm2. Biotic conditions were achieved by adding 1 mL of bacterial inoculum (108 cells.mL-1).

110

Then, the reactors were sealed with rubber plugs and aluminum caps and flushed with anaerobic

111

gas that was sterilized by passing through a 0.22 µm filter.

112

Sample analyses. Aqueous Fe concentration ([Fe]aq) was analyzed by inductively coupled

113

plasma optical emission spectrometry (ICP-OES, Varian VISTA-MPX) after 0.02 µm filtration

114

and 2% (v/v) HNO3 acidification. Analysis of H2 in the headspace was carried out by micro gas

115

chromatography (GC, Varian CP-4900) using a thermal conductivity detector with N2 as carrier

116

gas. The total H2 concentration ([H2]) was calculated as the sum of the contributions from the

117

gaseous and aqueous phases (determined using Henry’s law), normalized to the solution volume

118

to allow direct comparison with [Fe]aq. The experiments were usually performed in triplicate,

119

with two coupons used for the weight loss analysis, and one for the characterization of solid

120

corrosion products.

121

After experiment, all coupon samples were dried in an M-Braun LABstar MB10 anaerobic

122

glovebox (O2 concentration