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