Measurement of Carbonate Minerals in Aerosol Samples- A

Preliminary Study

Johann Engelbrecht

Desert Research Institute

X-ray Diffraction (XRD)

• XRD measures the presence and concentration of crystalline compounds (phases) such as minerals

• It does not record chemical concentrations

X-ray Diffraction (XRD) ScanRS611-38 µm

X-ray Diffraction (XRD) ScanRS611-PM10

X-ray Diffraction (XRD) ScanRS611-PM 2.5

X-ray Diffraction (XRD) ScanRS667-µm

X-ray Diffraction (XRD) ScanRS667-PM10

X-ray Diffraction (XRD) ScanRS646-38µm

X-ray Diffraction (XRD) ScanRS646-PM10

Minerals Identified in 20Re-suspended Aerosol Filter

Samples

• Quartz [SiO2] (common)

• Carbonate Minerals– Calcite [CaCO3]

– Aragonite [CaCO3]

– Dolomite [CaMg(CO3)2]

• Layered Silicates– Micas such as Muscovite– Vermiculite– Clays such as Dickite, Kaolinite &

Montmorillonite– Chlorite

Minerals Identified in 20 Re-suspended Aerosol Filter

Samples

• Feldspar Minerals– Anorthite– Microcline

• Oxides– Rutile

• Gypsum [CaSO4.2H2O]

Chemical vs Mineralogical Ratios

CAXC/SIXC vs Carbonate/Quartz

y = 0.5305x - 4.3187

R2 = 0.7639

0

100

200

300

0 100 200 300Carbonate/Quartz, XRD

CA

XC

/SIX

C,

Ch

emic

al

Chemical vs Mineralogical Ratios

CAAC/SIXC vs Carbonate/Quartz

y = 0.4333x - 3.741

R2 = 0.7315

0

100

200

300

0 100 200 300Carbonate/Quartz, XRD

CA

AC

/SIX

C,

Ch

emic

al

Soluble Ca vs Total Ca

CAAC vs CAXC

y = 0.8566x - 0.4067

R2 = 0.9007

0

4

8

12

16

20

0 4 8 12 16 20Calcium % by XRF

So

lub

le C

alci

um

% b

y A

A

Measured

All Soluble

Linear (Measured)

Linear (All Soluble)

Carbonate vs Soluble Ca

Carbonate vs CAAC

y = 0.9286x + 1.2187

R2 = 0.7327

0

8

16

24

32

0 8 16 24

Soluble Calcium by AA

Car

bo

nat

e %

by

TO

R

Measured

Theoretical

Linear (Measured)

Linear (Theoretical)

OC4 vs Soluble Ca

O4TC vs Soluble Calcium

y = 0.2006x + 0.0487

R2 = 0.3959

0

1

2

3

4

5

0 4 8 12 16 20 24

Soluble Calcium % by AA

O4T

C %

Carbonate vs Total Ca

Carbonate vs Calcium by XRF

y = 0.7552x + 1.1622

R2 = 0.5948

0

8

16

24

32

0 8 16 24Total Calcium % by XRF

Car

bo

nat

e %

by

TO

R

Measured

Theoretical

Linear (Measured)

Linear (Theoretical)

OC3 vs Total Ca

O3TC vs Total Calcium

y = 0.0244x + 0.894

R2 = 0.0574

0.0

0.4

0.8

1.2

1.6

2.0

0 4 8 12 16 20 24

Total Calcium % by XRF

O3T

C %

OC4 vs Total Ca

O4TC vs Total Calcium

y = 0.2118x - 0.3516

R2 = 0.5418

0

1

2

3

4

5

0 4 8 12 16 20

Total Calcium % by XRF

O4T

C %

OC4 vs Carbonate

O4TC vs C3TC

y = 0.1131x + 0.5249

R2 = 0.1481

0

1

2

3

4

5

0 8 16 24 32

C3TC % by TOR

O4T

C %

Chemical vs Mineralogical Ratios

Carbonate by TOR/SIXC vs Carbonate/Quartz

y = 0.3775x + 6.3167

R2 = 0.5755

0

100

200

300

0 100 200 300

Carbonate/Quartz, XRD

Car

bo

nat

e b

y T

OR

/SIX

C

Mineralogical Reactions

CaCO3 + SiO2 = CaSiO2 + CO2

calcite + quartz wollastonite

490 – 550 oC

Mineralogical Reactions

CaMg(CO3)2 + 4SiO2 + H20 =

dolomite + quartz + water

Mg3SiO4O10(OH)2 + 3CaCO3 + CO2

talc + calcite

150 – 250 oC

Question

• With the current TOR method, are we quantitatively measuring all the carbonate in the aerosol samples?

Conclusions

• Minerals can play an important role in aerosol samples which contain a significant amount of soil dust

• XRD is an appropriate analytical tool for identifying & quantifying minerals on filter samples, but does require research

• The TOR method for the measurement of mineral carbonate should be reviewed