Speciation of Individual Mineral Particles of Micrometer Size by the Combined Use of ATR-FT-IR Imaging and Quantitative ED-EPMA Techniques

Transcription

1 Speciation of Individual Mineral Particles of Micrometer Size by the ombined Use of ATR-FT-IR Imaging and Quantitative ED-EPMA Techniques Md Abdul Malek, Hae-Jin Jung, JiYeon Ryu, BoHwa Kim, Young-hul Song, HyeKyeong Kim, and hul-un Ro Department of hemistry Inha University, KREA

2 Airborne mineral dust particles Airborne mineral dust - the most abundant PM in coarse atmospheric aerosols Silicate minerals constitute ~90% of the Earth crust. Mineral dust plays multiple roles in influencing global climate (e.g., scattering and absorbing radiations, N). Heterogeneous chemical reactions can also alter the chemical balance of the atmosphere. Hygroscopic property of mineral dust can change their reactivity. Arid and semi-arid areas of the Saharan desert and central hina are the global scale sources.

3 haracterization of standard soil minerals Airborne mineral particles from soil minerals Soil minerals rarely exist in a single-phase, pure mineral form. Bulk FT-IR technique is a common practice for mineral analysis. Bulk analysis - not sufficient for the speciation of mixed minerals Analysis on a single-particle level can more clearly identify different mineral types. The combined use of ATR-FT-IR imaging and quantitative low-z particle EPMA techniques gives complementary information low-z particle EPMA on the morphology and elemental concentrations ATR-FT-IR imaging on mineral types The combined use of these two single-particle analytical techniques has great potential for the characterization of airborne mineral dust particles.

4 Low-Z particle EPMA (Electron Probe X-ray Microanalysis) for single particle analysis. SEM-EDX (Scanning Electron Microscopy Energy Dispersive X-ray Spectrometer) - Individual Particle Analysis shape and size : secondary / backscattered electron images chemical compositions : X-ray spectrum 2. Ultra-thin window EDX for low-z elements detection (e.g.,, N,, F) 3. Metallic collecting substrates for minimizing charging effect (e.g.,, Al) 4. Monte arlo calculation for Quantification 5. hemical speciation of aerosol particles Expert System

5 Monte arlo alculation for Quantification Measurement Simulation Electron detector Electron beam with 0 X-ray detector a a3 measured data Simulated SEM metal foil (arb. units) X-ray Energy () Measured and simulated spectra for a a 3 standard particle on a Be substrate

6 ATR-FT-IR imaging for single particle analysis ATR-FT-IR (Attenuated Total Reflectance-FT-IR Spectrometry) - Individual Particle Analysis location : optical image functional groups, molecular species, and crystal structure : IR spectra Dual detector Visible radiation d = 600 μm ATR imaging accessory assegrain system Motorized sample stage Ge crystal sample contact surface sample IR radiation Ge crystal for imaging

7 ATR-FT-IR Imaging for Single Particle Analysis

8 ATR-FT-IR and XRD measurements of minerals ATR-FT-IR measurement Perkin Elmer Spectrum 00 FT-IR spectrometer Spectrum Spotlight 400 FT-IR optical microscope ATR accessory: Ge IRE crystal, diam. = 600 μm, RI = 4 A 6 x pixel Mercury admium Telluride (MT) array detector Pixel size of.56 μm Spectral resolution of 4 cm - at the range of 720 to 4000 cm - Spatial resolution 3.9±0.5 µm at cm - XRD measurement Philips X pert MPD powder X-ray diffractometer u Kα radiation Scanning range of 2θ is 3-65 o scanning speed is 0.02 o /s, a step size of 2θ is 0.02 o

9 Major minerals obtained by XRD for 24 mineral samples Major mineral types by XRD Number of samples Source of sample microcline (K-feldspar) 2 NIST, KIGAM muscovite 4 KIGAM montmorillonite 2 KIGAM kaolinite 3 KIGAM talc 2 KIGAM heulandite KIGAM biotite KIGAM Mg-vermiculite KIGAM pyrophyllite KIGAM cristobalite (Si 2 ) KIGAM quartz (Si 2 ) Aldrich apatite Aldrich calcite Aldrich gypsum Aldrich anhydrous as 4 Aldrich magnesiumhydroxycarbonate hydrate Aldrich Total 24 NIST : National Institute of Standards and Technology, USA KIGAM : Korea Institute of Geoscience and Mineral Resources

10 Major microcline (K-feldspar (KAlSi 3 8 ) ) XRD spectrum of K-feldspar NIST SRM mineral sample. counts/s Minors albite (Na-feldspar (NaAlSi 3 8 ) ) quartz (Si 2 ) counts/s θ θ Majors muscovite (KAl 2 (Si 3 Al) 0 (H,F) 2 ) quartz (Si 2 ) Minors + montmorillonite ((0.5a,Na) 0.7 (Al,Mg,Fe) 4 [(Si,Al) 8 20 ] (H) 4. nh 2 ) albite (Na-feldspar (NaAlSi 3 8 )) orthoclase (K-feldspar (KAlSi 3 8 )) kaolinite (Al 2 Si 2 5 (H) 4 ) XRD spectrum of a mineral sample of muscovite and quartz.

11 SE images (A) before and (B) after ATR-FT-IR measurement and ATR-FT-IR images obtained () by a PA analysis and (D) for transmittance signal at 000 cm- (K-feldspar SRM mineral on foil) (A) Δ Δ Δ (D) () () (B)

12 Typical X-ray spectra and elemental concentrations of different feldspars observed in K-feldspar SRM mineral sample (A) Al Si K particle #5 (K-feldspar) Diameter: 5.46 µm Al 8.5 Si 26.2 K (B) Na Al Si particle #2 (Na-feldspar) Diameter: 3.63 µm Na 8.2 Al 9.5 Si () Na Al Si K particle #22 ((Na, K)-feldspar) Diameter: 2.2 µm Na 2.9 Al 9.0 Si 25.6 K (D) Fe Si Al K particle #9 ((K, Fe)-feldspar) Diameter:.79 µm Al 5.0 Si 23.7 K 4.4 Fe 3.4 Fe

13 Typical ATR-FT-IR spectra of different feldspars observed in K-feldspar SRM mineral sample. (onventional transmission FT-IR spectra of K- and Na-feldspar bulk samples reported by the other study and an ATR-FT-IR spectrum obtained from bulk K-feldspar SRM mineral powder are also shown in an inset.) A A transmission FT-IR spectrum of Na-feldspar transmission FT-IR spectrum of K-feldspar :Si- 63:Si- ATR-FT-IR spectrum of K-feldspar SRM Mineral :Si(Al)- 09: Si :Si(Al)- 00:Si(Al) Matteson et. al., J. Sediment. Petrol. 993, 63, : Si-Si 788: Si-Si 747: Si-(Al)Si 725: Si-(Al)Si :Si(Al)- 039:Si(Al)- 33: Si- 6:Si- 33:Si- 003:Si(Al)- 06:Si(Al)- 770: Si-Si 729: Si-(Al)Si wavenumber, cm - particle #5 (K-feldspar) particle #22 ((Na, K)-feldspar) particle #2 (Na-feldspar) particle #9 ((K, Fe)-feldspar) wavenumber, cm -

14 SEIs SEM (A) before and (B) after ATR-FT-IR measurement and ATR-FT-IR images obtained () by a PA analysis and (D) for transmittance signal at 030 cm- of a muscovite mineral sample on foil. (A) (B) 2 2 (MUS) 5 5 (Q) () 4 (MN) (Q) 24 (KA) (Q) 2 (Na-F) (D) 3 4 (MUS) 7 (MUS) 22 (K-F) 2 5 (K-F) 4 (K-F) (MUS) 8 (MN) (Na-F) 6 (MN) (MUS) 9 (Q) 2 (MN) 3 (Q) (K-F) 4 (K-F) (MN) (K-F) (MN: montmorillonite, MUS: muscovite, Q: quartz, Na-F: albite, K-F: orthoclase (K-feldspar), KA: kaolinite)

15 Typical X-ray spectra and elemental concentrations of different minerals observed in a muscovite sample (A) Si Al K particle # (K-feldspar) Diameter: 3.85 µm Al.5 Si 30.8 K (B) Al Si Mg K particle #2 (muscovite) Diameter: 4.4 µm Mg 0.5 Al 4.8 Si 7.8 K.5 Fe 2. Fe () Al Si Mg particle #3 (montmorillonite) Diameter: 2.06 µm Mg.4 Al 3.3 Si 7.8 Fe (D) Al Si particle #3 (quartz) Diameter: 4.4 µm Al 0.6 Si Fe (E) Si Al Na particle #2 (Na-feldspar) Diameter: 2.6 µm Na 5.8 Al.4 Si (F) Al Si Mg particle #24 (kaolinite) Diameter: 3.82 µm Mg.2 Al 4.8 Si 20.0 Fe 2.6 Fe

16 Typical ATR-FT-IR spectra of different minerals observed in a muscovite mineral sample. (An ATR-FT-IR spectrum obtained from bulk powder of this sample is also shown in an inset.) % T % T : -H 3620: -H wavenumber, cm - 638: H 2 997: Si- (MN, KA, MUS) Si(Al)- (feldspar) 720 particle #2 (Na-feldspar) particle # (K-feldspar) particle #24 (kaolinite) particle #3 (montmorillonite) particle #2 (muscovite) particle #3 (quartz) & 777: Si- (Q, KA); Si-Si (feldspar) 908: AlAl-H (MN, KA, MUS) : Si- 046: Si : Si : AlAl-H : Si- 793: Si wavenumber, cm - (MN: montmorillonite, MUS: muscovite, KA: kaolinite, Q: quartz)

17 Summary Total samples analyzed: 24 Data presented herein: 2 samples K-feldspar SRM sample According to NIST specification, K-feldspar SRM sample consists of 80~85 % microcline, and 0~5 % albite Based on X-ray and ATR-FT-IR spectral data of 29 individual particles, 5 particles were identified as K-feldspar 5 particles as Na-feldspar 8 particles as (Na,K)-feldspar, and particle as (K,Fe)-feldspar Muscovite and quartz sample For the muscovite and quartz sample, among 24 individual particles 6 particles are observed as muscovite 5 particles as quartz 5 particles as K-feldspar 5 particles as montmorillonite 2 particles as Na-feldspar particle as kaolinite Different types of minerals were observed in the remaining 22 samples except samples collected from Aldrich A manuscript was submitted to Anal. hem., where data for 22 mineral samples can be found. Soil samples collected from various arid areas in hina, and ambient aerosol samples are under investigation.

18 onclusions The combined use of ATR-FT-IR imaging and low-z particle EPMA allows unambiguous identification of different minerals. ATR-FT-IR imaging provides information on molecular and crystal structure, functional group, and physical state. Low-Z particle EPMA gives information on morphology and quantitative elemental concentrations. Analysis on single particle basis gives more detailed information than bulk analysis. It has great potential in elucidating the characteristics of soil-derived individual airborne particles. ur future project is to build up a good archive of mineral s FT-IR spectra for the facile assignment of soil-derived individual airborne particles. (For low-z particle EPMA, a library building is not necessary for X-ray spectra, which is an advantage over FT-IR technique.)

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