Synchrotron Radiation & Environmental Science

Transcription

1 Scuola SILS, Grado, settembre 2013 Synchrotron Radiation & Environmental Science Pierfranco Lattanzi Università di Cagliari

2 What is environmental science? very broad umbrella covering any phenomenon that may have an impact on life Includes practically all other sciences obviously life sciences and physical sciences (chemistry, earth sciences, physics.) Truly interdisciplinary approach

3 The science of the complexity Typically complex systems, with many parameters of very different nature Typical non linear and/or chaotic effects! Butterfly effect (does the flap of a butterfly wings in Brazil set off a tornado in Texas?) Most studies, especially in the early stages, were descriptive/empirical

4 Contaminant cycle

5 Molecular environmental science speciation, distribution, reactivity, transformations, mobility, biogeochemical cycling, and bioavailability of environmental contaminants ultimately depend on molecular-scale structure and properties (MES)

6 MES

7 Synchrotron-based MES ~ 30 yrs (mostly post 1990) Hundreds (=> thousands) of publications 2(3) dedicated beamlines - SSRL, ALS (APS) Envirosync group (USA ~ 400 persons) Regular meetings (SES last in Saskatoon, June 2011 seventeen lectures, + poster presentations)

8 MES research at SSRL

9 MES at ALS

10 Reviews in mineralogy and geochemistry, vol. 49 (2002) Mineralogical Magazine, February 2008, Vol. 72(1)

11 How do environmental scientists use synchrotron radiation? Localization of (often very dilute) contaminant species in (often very complex) environmental samples (X-ray imaging) speciation (chemical and structural state) of contaminant(s) (XAS, XRD) Surface and interface studies (SR-XPS, XSW, X-ray reflectivity, GIXAS.) Dynamic (time-resolved) in situ studies

12 Chemical speciation of contaminants

13 XAS discrimination of chromium valence states

14 Chemical speciation of plutonium by XAS

15 This work helped demonstrate that soluble transport models are not applicable to Pu migration in RFETS soils, and that particulate (i.e., erosion) transport is the dominant transport mechanism for Pu migration at the site. This prediction translates directly into very substantial cost savings, because focuses efforts toward erosion modeling, and future land configuration studies to control particulate transport. It will also help define cleanup levels Thus Pu XAFS measurements have developed into a decision-making tool that saved the company millions of dollars by focusing site-directed efforts in the correct areas, and will aid the DOE in its efforts to clean up and close the RFETS

16 More of plutonium (µ-sxrf) Yucca mountain HLRW site

17 Microdistribution of metals in environmental samples

18 mercury distribution in fish organs

19

20 Adsorption of Co, U on calcite crystal faces

21 Heavy metals in grass roots X-ray microtomography study

22 A scanning transmission X-ray spectromicroscopy study of distribution of Fe oxidation states in green rust

23 Biofilms & metals An XSW study of interaction of Pb with biofilms grown on metal oxides

24 Feldspar water interaction In situ study at various ph by X- ray reflectivity

25 Arsenic uptake by natural calcite: a XAS study

26 Arsenic poisoning map Main geochemical control Fe-oxyhydroxides

27 Arsenic in natural calcite (Southern Tuscany, Italy) All scale study Geology Mineralogy Petrography Chemistry Spectroscopy

28 Natural As-bearing (travertine) calcite in Tuscany Pecora River Valley

29 Ore Deposits in Tuscany Alpi Apuane Fe, py,ba; Hg; Cu(Fe); Pb,Zn,Ag.. Montecatini V.C. Cu Campigliese Cu,Pb,Zn,Ag; Sn; Fe Colline M.re Cu,Pb,Zn,Ag py M. Amiata Hg Elba Fe, py Mancianese Sb, Au Pecora River Valley

30 Geochemical prospection for Au: Pecora River stream sediments chemistry ( ) Pecora Valley

31 Geogenic anthropogenic (modern vs. ancient) anomaly Casone industrial site FeS2+O2=SO2+Fe-ox SO3+H2O=H2SO4

32 Pecora River Valley geological sketch PECORA RIVER SCARLINO SCALO VALPIANA FOLLONICA CASONE SCARLINO Basement MAX 200 m BASEMENT AUTOCHTHON (Quaternary) Clays Sands Gravels

33 ARSENIC DISTRIBUTION IN THE PECORA VALLEY SEDIMENTS Present day alluvial sediments (Pecora R.) 275 ppm Pebbles and gravels 3 39 ppm Paleo-Pecora Alluvial fan ppm Travertine ppm Basement 13 ppm NO SE ( not in scale) O Arsenic has a natural origin Costagliola et al. Chemical Geology 2010 E

34 Arsenic in calcite? Could be of extreme environmental significance even if in low amounts Calcite is one of the most common minerals at the Earth s surface Bulk evidence in our rocks from sequential extraction (As in calcite ~ mg/kg)

35 Arsenic in calcite: state of the art

36 Travertine outcrops Travertines Palaeo Pecora alluvial fan

37 Materials & Methods Materials travertine carbonatic tufa (paleo lake) Mineralogy: abundant calcite, minor quartz, Fe-oxyhydroxides, silicates Methods Sequential extractions Spectroscopic investigations: local micro-environment of arsenic Electron Paramagnetic Resonance (EPR)/Electron Spin Echo (ESE) X-ray Absorption Spectroscopy X-ray Microfluorescence (µ-xrf) and

38 EPR-ESE (Electron Paramagnetic Resonance-Electron Spin XAS -Element specific Echo) and XAS comparison ESE -Mineral specific (EPR) - As oxidation state (XANES) X - Local environment of (MnII) - As local environment (EXAFS) - No interference from Ca, C and O EPR-ESE facility in Florence is under construction

39 EPR-ESE spectra interpretation As-Mn(II) distance 3.2 Å No protonic modulation (H 2 O adsorbed onto surface): As is in the structure => no HAsO 2-3 Axial interaction : As is tricoordinated As oxidation state???????? 2 CO 3 AsO 3 3

40 As K-edge XAS: XANES - Samples are highly heterogeneous: natural stuff! - We detected both As(III) and As(V) in travertine Arsenic is at least in two sites in one or more minerals Absorption As(V) As(III) As2O3 Na-arsenite Sample 2 As2O5 Na-arsenate Ca-arsenate Scorodite Ferrihydrite Sample Energy (ev)

41 µ-xrf maps µ-xanes spectra

42 Indagini As K-edge XAS:EXAFS -As(V): no second shell (sample1) 5 1 Sample 1 -As(III/V): second shell is evident, first is shell structured (sample2) -As(V) in Fe-oxyhydrox. FT moduli k*χ(k) Ferrihydrite Sample k (Å -1 ) Sample 1 -Correlations As-Ca is present R (Å) Ferrihydrite Sample 2

43 XAS: As-Ca distances Two possible distances 3.05 Å 3.37 Å The C-Ca distance in calcite is about 3.20 Å EPR-ESE: As-Ca distance is about 3.20 Å Why two distances in As-bearing calcite?

44 As in the calcite structure (synthetic As bearing calcite) Cheng et al., (1999) 0.57Å Roman Ross et al., (2006) Long dist. Short dist.

45 As-Ca distances As offset Using an offset of 0.57Å (Roman Ross et al., 2006) calculations (*) show that: As-Ca short = 2.99 Å (XAS=3.05 Å) As-Ca long = 3.49 Å (XAS=3.37 Å) Fixing the As-Ca distances obtained by XAS, the offset is 0.36 Å ( * ) assuming an hard sphere model

46 SR-XRPD Cell parameters of As bearing calcite: a 0 0.2% shorter than pure calcite c 0 0.1% longer that pure calcite Possible expansion due to As substitution (Role of bioprecipitation? )

47 Conclusions Arsenic is partly associated to oxyhydroxides (extractions), most probably as As(V) (XAS) Arsenic is also hosted in calcite (extractions, EPR- ESE, XAS) in its As(III) oxidation state (As K-edge XANES) Possible substitution: CO 2-3 AsO 3-3 Arsenic-bearing calcite shows a deformed cell: steric effects AsO 3-3 oxyanions? (XRPD)

48 Open questions Which is the actual substitution? CO 2-3 AsO 3-3 or CO 2-3 HAsO 2-3? (EPR-ESE in synthetic Mn-As doped calcite) Possible role of Mn 2+ (EPR-ESE in synthetic Eu 2+ -As doped calcite) Possible role of biogenic precipitation As-travertine connection in natural systems (studies on other samples)