Specific Surface Area of Soil
-
Upload
martin-anikwe -
Category
Documents
-
view
220 -
download
0
Transcript of Specific Surface Area of Soil
-
8/12/2019 Specific Surface Area of Soil
1/19
Measuring Specific Surface Area ofSoils and Soil Minerals by Water
Vapor AdsorptionYusuf Setiawan
Dr. Christopher Amrheins LabSoil Chemistry
Department of Environmental Science
-
8/12/2019 Specific Surface Area of Soil
2/19
Introduction
Surface area is related to many physical andchemical properties of soils.
Reactive surfaces in soils vary widely becauseof the differences in mineralogical and organiccomposition, as well as in particle-sizedistribution.
-
8/12/2019 Specific Surface Area of Soil
3/19
Soil Texture
SandSilt
Clay
2 mm - 50 m50 -2 m
< 2 m
-
8/12/2019 Specific Surface Area of Soil
4/19
Specific Surface Area
Surface area per unit mass of soil
Expressed as square meter per gram soil
(m2
g-1
).
-
8/12/2019 Specific Surface Area of Soil
5/19
Implications of Surface Area
Cations Exchange Capacity (CEC)
Water retention and movement
Heavy metal and pesticide adsorption
Nutrients and Irrigation management
-
8/12/2019 Specific Surface Area of Soil
6/19
Traditional Methods
N2-gas Measures only the external surface area Requires a specialized instrument
EGME (Ethylene Glycol Monoethyl Ether) Measures total surface area (internal and external) Limited to a single partial pressure (P/Po) equilibrium Samples cannot be used multiple times Time intensive
-
8/12/2019 Specific Surface Area of Soil
7/19
Water Vapor Adsorption Method
Soils weight and partial pressure can be measured quickly
Saturated salt solutions control relative humidity
Water adsorption forms monolayer surface area calculated
Water potentiameter measures relative vapor pressure (P/P 0)
-
8/12/2019 Specific Surface Area of Soil
8/19
Research Objectives
1. Compare surface area measured from watervapor adsorption compared to the EGMEmethod.
2. Compare surface area of soils saturated withdifferent cations.
-
8/12/2019 Specific Surface Area of Soil
9/19
Soils Involved in the Experiment Kaolinite (1:1 clay mineral)
Montmorillonite (2:1 clay mineral)
Grangeville
Holland and Merced soils saturated with various cations: NaCl
KCl MgCl2 CaCl2
-
8/12/2019 Specific Surface Area of Soil
10/19
Method Different soil types placed in a vacuum chamber with salts
Saturated salt control different relative humidity:
NaOH (8%) LiCl (11%) CaBr2 (20%) K-Ac3 (24%) CaCl2 (32%) LiNO3 (48%)
-
8/12/2019 Specific Surface Area of Soil
11/19
Relative Humidity Chamber
-
8/12/2019 Specific Surface Area of Soil
12/19
Decagon WP4C DewpointPotentiameter
-
8/12/2019 Specific Surface Area of Soil
13/19
How do we know soils have reachedequilibrium?
Weight of soils does not change.
Water Potential ( ) measurement for soils does notchange
-350
-300
-250
-200
-150
-100
-50
01 2 3 4 5 6 7 8
M a t r i c P o t e n t i a l
( - M
P a )
Time (days)
Kaolinite Matric Potential
8% Humidity
20% Humidity
32% humidity
-
8/12/2019 Specific Surface Area of Soil
14/19
Adsorbed Water Weight atDifferent Partial Pressure
Surface area is calculated within the partialpressure (P/Po) of 0.05 to 0.45.
-
8/12/2019 Specific Surface Area of Soil
15/19
Linearized Surface Area Curve forWater Vapor Adsorption
y = 334.73x + 12.605R = 0.8887
0
20
40
60
80
100
120
140
160
180
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
1 / [ V a *
( P o
/ P - 1
) ]
Relative Humidity (P/Po)
Kaolinite
Kaolinite
Linear (Kaolinite)
-
8/12/2019 Specific Surface Area of Soil
16/19
Comparison of Surface AreaMeasurement
Soil Type Water VaporAdsorption
Surface Area
(m2
g-1
)
EGMESurface Area
(m2
g-1
)
Kaolinite 8 7Montmorillonite 348 305
Grangeville 23 16Merced 163 154Holland 142 108
-
8/12/2019 Specific Surface Area of Soil
17/19
Comparison of Surface AreaMeasurement
Soil Type Water VaporAdsorption
Surface Area(m
2g
-1)
EGMESurface Area
(m2
g-1
)
Na+ Merced 108 137K
+Merced 94 112
Mg2+
Merced 124 124
Ca2+
Merced 126 130Na+
Holland 210 102K
+Holland 96 103
Mg2+
Holland 86 92
Ca2+
Holland 57 96
-
8/12/2019 Specific Surface Area of Soil
18/19
Conclusion
Water vapor adsorption method iscomparable to the EGME method.
Water vapor method is very easy and quick todetermine surface area of soils.
Surface area measurements of the soilssaturated with different cations showed notrend.
-
8/12/2019 Specific Surface Area of Soil
19/19
Acknowledgements
Dr. Christopher Amrhein
Myles Davis
Kearney Foundation