Environmetal Soil Properties and Behaviour

Environmetal Soil Properties and Behaviour


DisciplinaControle e Remediação da Poluição dos Solos5 materiais18 seguidores
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including 
polysaccharides, polypeptides, aliphatic chains, and aromatic lignin frag-
ments as the major components based on the concept of micellar structure 
(Simpson et al., 2002). However, Asutton and Sposito (2005) have suggested 
that as the supramolecule association model does not elucidate and does not 
explain the changes in functional group composition occurring with separa-
tion of humic substances into different apparent mass or size fractions, \u201cwe 
need better information about the hydrophobic and H-bonding interactions 
that hold together humic aggregates of various sizes.\u201d
2.4.2.2 Surface Functional Groups
As opposed to clay minerals, which have hydroxylated surfaces with OH 
functional groups, soil organic matter exhibits a greater variety of surface 
functional groups. The sketch shown in Figure  2.8 illustrates some of the 
more common types of functional groups. The most common functional 
groups are hydroxyls, carboxyls, phenolics, and amines. The carboxyl group 
Extract organics with 0.5
N HCl for 23 h under
nitrogen atmosphere
Soil
Centrifuge
Centrifuge
Humin Humin
Centrifuge
Non Humic
Fraction
Discard
Centrifuge
Centrifuge
Fulvic Acid Humic Acid
Precipitate
Extract with 0.5
N NaOH,
23 h nitrogen
atmosphere
Soluble Insoluble
Buffer to pH 2
with 8N HCl
Supernatant
Buffer to pH 10
with 10 N NaOH
Precipitate Supernatant
Add ethanol
Supernatant PrecipitateSupernatantPrecipitate
FIguRE 2.7
Extraction technique for determination of humic and fulvic acids, and humins.
44 Environmental Soil Properties and Behaviour
is the major contributor to the acidic properties of the soil organics. Carbon 
and nitrogen combine with oxygen or hydrogen to form the various types of 
surface functional groups shown in the diagram.
These functional groups control most of the properties of organic mole-
cules that constitute the soil organic materials, and also their reactions with 
other soil fractions in a soil\u2013water system. Depending on the pH of the soil 
and their respective pKa or pKb (their respective log acidity and log basicity 
constants), they can protonate or deprotonate (develop positive or negative 
charges). The decrease in aromaticity between humic acids, fulvic acids, and 
humins reflects the biodegradation sequence of humus, beginning with deg-
radation of nonamorphous organics into humic acids, and continuing on to 
fulvic acids and finally humins.
Many of the different types of functional groups have been detected in the 
study of IR spectra information on tests on a soil organic reported by Yong and 
Mourato (1988), the details of which are shown in Table 2.2. These surface func-
tional groups are classed as organic molecular units and cannot be diluted 
since they are part of the organic matter itself. Nonhumic materials of soil 
organics are generally composed of large numbers of aliphatic rings typical 
of polysaccharides such as those detected in the samples tested in the study. 
Because of the large variation or differences in the composition of soil organic 
Hydroxyl
OH\u2013
NH+x
Amine
Carbonyl
CO+
Carboxyl
COOH\u2013
OH\u2013
Phenolic
Organic Matter
Macromolecule 
O
O
Quinone
FIguRE 2.8
Some typical functional groups associated with soil organic matter. (Adapted from Yong, R.N., 
2001, Geoenvironmental Engineering: Contaminated Soils, Pollutant Fate, and Mitigation, CRC Press, 
Boca Raton, FL, 307 pp.)
45Nature of Soils
matter, due to the differences in source material and decomposition processes, 
there will be wide ranges and values for the proportions of each of the kinds 
of functional groups shown in Figure 2.8. In addition, variations in the type 
of extraction and testing procedures will also contribute to the wide range of 
values reported, as seen for example in the values shown in Table 2.3.
TAbLE 2.2
IR Spectra of Organic Fractions Extracted from Soil Material Obtained from a Site
Adsorption 
Band (cm\u22121) Organic Fraction Description
3400 All fractions OH stretching of free hydroxyls and hydration 
molecules
3000\u20132800 Fulvic acids, humins Aliphatic C\u2013H bonds
2200\u20132100 Humic acids, humins COOH vibrations
1725 Humic acids, humins C=O stretching of fluvic acids\u2019 COOH and ketones
1600 (large) Humic acids, fulvic 
acids, humins
Aromatic bonds and some overlapping of strongly 
H-bonded C=O groups
1600 (small) Nonhumic fractions C\u2013H deformations of aliphatic groups
1400 (large) Nonhumic fractions C\u2013H deformations of aliphatic groups
1400 (small) Humic acids, fulvic 
acids, humins
C\u2013H deformations
1240 All fractions C\u2013H stretching and OH deformation of COOH
1140 All fractions OH deformation of phenolic and alcoholic functional 
groups
1100\u20131000 Nonhumic fractions Polymeric carbohydrates
950\u2013450 Humins Vibration of aluminium and silicon elements
Source: Adapted from Yong, R.N., and Mourato, D., 1988, Can. Geotech. J., 25:599\u2013607.
TAbLE 2.3
Composition and Functional Groups for Fulvic Acid, Humic Acid, and Humin
Fulvic Acid Humic Acid Humin
% Carbon content 40\u201350 50\u201360 50\u201360
% Oxygen 40\u201350 30\u201340 30\u201335
% Hydrogen 4\u20137 3\u20136 NA
Carbonyl, % up to 5 up to about 4 NA
Carboxyl, % 1\u20136 3\u201310 NA
Quinone, % 2± 1\u20132 NA
Ketones, % 2± 1\u20134 NA
Alcoholic OH, % 2.5\u20134 up to 2 NA
Phenolic OH, % 2\u20136 up to about 4 NA
Source: Selection of data from Griffith, S.M., and Schnitzer, M., 1975, Soil Sci. Soc. Amer. J., 
39:861\u2013869; Schnitzer, M. et al., 1973, Soil Sci. Amer. Proc. 7:229\u2013326; Hatcher, P.G. 
et al., 1981, Soil Sci. Soc. Amer. J. 45:1089\u20131094.
46 Environmental Soil Properties and Behaviour
Soil organic materials contain some sulphur in the range of 0% to 2% 
for humic acids and up to about 4% for fulvic acids. Since hydrogen in the 
oxygen-containing functional groups can be dissociated, the surface func-
tional groups will provide the material with acidic properties. By and large, 
carboxyls and phenolic OH groups contribute significantly to the cation 
exchange capacity (CEC) of the soil organic material, and are considered to 
be the most important functional groups. They contribute significantly to 
the source of negative charge, which has been reported to range from 2 to 4 
mEq/g (Greenland and Hayes, 1985). This compares with the charge range of 
0.01 to 2 mEq/g for clay minerals.
2.5 Soil Particles
The soil particle properties of interest in the study of soil properties and behav-
iour are those that relate directly to particle interaction in the presence of pore-
water. These include (a) texture of soil particles, (b) surface functional groups 
associated with the electrical charges of soil particles, (c) cation exchange 
capacity, CEC, and (d) specific surface area, SSA. Although particle size and 
shape do not strictly qualify as surface properties, they will be included in 
this discussion because they relate directly to soil properties and behaviour 
such as specific surface area, soil density, and compaction of soils. The term 
particles is used here to include all the soil solids constituting the various soil 
fractions. There is a direct link between soil particle properties and many 
physical, mechanical, and physical-chemical properties, and environmentally 
associated evolution of soils. The links will become clearer when we discuss 
these properties and behaviour in the later chapters of this book.
2.5.1 Size, Shape, and Texture of Particles
2.5.1.1 Size and Shape
The size, shape, and texture of a soil particle are directly related to the mor-
phology of soils, density, permeability, hardness, strength, and their hyster-
etic performance in response to external forces. The important items of note 
include the following:
\u2022	 For particle sizes larger than clays and fine silts, size and shape go 
almost hand in hand; the composition of these particles, such as 
quartz, feldspar, chert, will