Environmental Engineering Reference
In-Depth Information
9.2.2.
Nonmetal Compounds in Soil
The nonmetals in soil include compounds of carbon, oxygen, nitrogen, chlorine, silicon,
phosphorous, sulfur, bromine, iodine, arsenic, fluorine, and selenium. A number of
inorganic carbon compounds, such as carbon dioxide and carbonates, occur in soil. The
vast majority of carbon compounds in soil are organic, however, and will be discussed in
the section on organic compounds below. Oxygen occurs in carbon dioxide, but also
more importantly in water. Water is a unique and critical component in the environment
and will be discussed in the next section. Oxygen occurs in carbon monoxide and ozone,
which is important in both the upper and lower atmosphere. Oxygen also occurs in all the
oxyanions.
Nitrogen can occur in several different types of inorganic compounds in the
environment. These will commonly be compounds of ammonia, ammonium, nitrite or
nitrate, and various nitrogen oxides. Although other nitrogen compounds have been
reported in the environment, they are generally in low concentration and do not gain
much attention from environmentalists. Any time an unusual amount of any type of
nitrogen compound is found in any environmental sample there is cause for concern.
Phosphorus is found bonded to oxygen, forming phosphates. Most often phosphates
are formed as combinations with calcium to produce various calcium phosphates. These
may also have other elements associated with them, such as hydrogen, fluorine,
aluminum, and iron, forming other naturally occurring phosphates.
Both chlorine and bromine are commonly found in the environment. Their
concentrations increase as one moves toward the oceans or salt deposits. Both are
commonly combined with alkali metals to form salts. These salts are highly water soluble
and are easily and rapidly leached from soil during its formation. Eventually these salts
are deposited in the oceans [12].
S
ilicon is almost exclusively found as silicon dioxide (SiO
2
) and silicates in the
environment. In silicates it takes a tetrahedral form in the center of four oxygens, which
bond to other constituents, such as aluminum. In this way it is an integral part of soil
minerals in the sand, silt, and clay fractions.
9.2.3.
Metal Cations
The alkali and alkaline earth elements form simple positive cations. The alkali metals
lithium (Li
+
), sodium (Na
+
), potassium (K
+
), rubidium (Rb
+
), and cesium (Cs
+
) form ions
with a single positive charge or oxidation state. The alkaline earth metals magnesium
(Mg
2+
), calcium (Ca
2+
), strontium (Sr
2+
), and barium (Ba
2+
) occur as simple cations with
two positive charges or an oxidation state of 2
+
. Aluminum is found only in the 3
+
oxidation state. Other metals, such as chromium, manganese, iron, cobalt, nickel, and
copper can occur in two or more oxidation states. For these elements not only is their
presence important but also their oxidation state. Iron II (Fe
2+
) is more soluble than iron
III (Fe
3+
). Chromium IV (Cr
6+
) is considered to be more toxic than chromium III (Cr
3+
),
thus the form or species of an element is as important or more important than simply its
presence.
High concentrations of lithium, sodium, and potassium are associated with high soil
Search WWH ::
Custom Search