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9.1 Introduction
Metals are present in all the parts of our environment. Some of the metals at certain
levels are important for maintaining life functions, while some metals can be harmful to the human body. The presence of heavy metals in water resources can be of
geogenic or anthropogenic origin. The industrial production takes part with the largest percent emission of heavy metals, which are of anthropogenic origin. Many of
the metals are toxic even in very low concentrations, due to their potential to accumulate in the living organisms and thus enter the food chain. Heavy metals released
into the aquatic environment are mostly tied to deferred materials, and they eventually accumulate in sediments (Tchobanoglous et al. 2003; Grady Jr et al. 2011).
Among the various metals such as heavy metals that occur as most toxic pollutant of wastewater, chromium is ranked as one with the highest toxicity. The
toxic effect of chromium is correlated with its valence. The six-valent chromium
Cr(VI) is toxic to all life forms and is considered the main pollutant (Norseth
1981; Toxicological Profile for Chromium 1991; Cieslak-Golonka 1995; Myers
et al. 2000; Zhitkovich et al. 2002; Dupont and Guillon 2003). Cr(VI) is used in
many industries such as the manufacturing of paints, metalworks, manufacture of
automobile parts, and in the petrochemical industry (Chakir et al. 2002).
Wastewater from these industries contains significant quantities of chromium that
is spread in the environment through land and water and eventually accumulates
through the food chain. It is soluble in water and can adsorb in living organisms.
When it accumulates in living organisms, it can cause major health problems.
Exposure to lower concentrations may cause lung tumor and liver, kidney, and
other reproductive problems. The International Agency for Research on Cancer
has classified chromium as a carcinogen (Biswajit et al. 2013). Hexavalent form
of chromium, Cr(VI) is the most damaging for the health of humans due to its
carcinogen and mutagenic properties. Therefore, there are legal regulations governing the permitted amounts of heavy metals that are found in water resources,
depending on their further use. Of particular importance are defined MAC values
(maximum permissible concentrations) for each element separately, which are the
result of extensive consultation of the scientific research literature and represent
the prescribed standards. Although the limit for Cr(VI) in the wastewater is only
0.05 mg/L, the actual found amounts are much higher (Case Studies in
Environmental Medicine: Chromium toxicity 2000).
In recent years, adsorption proves to be an alternative method for the removal of
metal ions from the wastewaters, including the Cr(VI). To reduce capital costs, there
have been major studies on the use of cheaper adsorbents which may be different
types of soils and clays. Removal of heavy metals with the use of soils is performed
based on the great adsorption capacity of the negatively charged parts of the soil and
the possibility of formation of complex molecules with organic molecules that are
located in the soil and thus resulting in the formation of oxides, hydroxides, and
other insoluble minerals. Clays show such properties, as a result of their chemical
and mechanical stability, large surface area, permanent negative voltage, and other
H. Memedi et al.
9.1 Introduction
Metals are present in all the parts of our environment. Some of the metals at certain
levels are important for maintaining life functions, while some metals can be harmful to the human body. The presence of heavy metals in water resources can be of
geogenic or anthropogenic origin. The industrial production takes part with the largest percent emission of heavy metals, which are of anthropogenic origin. Many of
the metals are toxic even in very low concentrations, due to their potential to accumulate in the living organisms and thus enter the food chain. Heavy metals released
into the aquatic environment are mostly tied to deferred materials, and they eventually accumulate in sediments (Tchobanoglous et al. 2003; Grady Jr et al. 2011).
Among the various metals such as heavy metals that occur as most toxic pollutant of wastewater, chromium is ranked as one with the highest toxicity. The
toxic effect of chromium is correlated with its valence. The six-valent chromium
Cr(VI) is toxic to all life forms and is considered the main pollutant (Norseth
1981; Toxicological Profile for Chromium 1991; Cieslak-Golonka 1995; Myers
et al. 2000; Zhitkovich et al. 2002; Dupont and Guillon 2003). Cr(VI) is used in
many industries such as the manufacturing of paints, metalworks, manufacture of
automobile parts, and in the petrochemical industry (Chakir et al. 2002).
Wastewater from these industries contains significant quantities of chromium that
is spread in the environment through land and water and eventually accumulates
through the food chain. It is soluble in water and can adsorb in living organisms.
When it accumulates in living organisms, it can cause major health problems.
Exposure to lower concentrations may cause lung tumor and liver, kidney, and
other reproductive problems. The International Agency for Research on Cancer
has classified chromium as a carcinogen (Biswajit et al. 2013). Hexavalent form
of chromium, Cr(VI) is the most damaging for the health of humans due to its
carcinogen and mutagenic properties. Therefore, there are legal regulations governing the permitted amounts of heavy metals that are found in water resources,
depending on their further use. Of particular importance are defined MAC values
(maximum permissible concentrations) for each element separately, which are the
result of extensive consultation of the scientific research literature and represent
the prescribed standards. Although the limit for Cr(VI) in the wastewater is only
0.05 mg/L, the actual found amounts are much higher (Case Studies in
Environmental Medicine: Chromium toxicity 2000).
In recent years, adsorption proves to be an alternative method for the removal of
metal ions from the wastewaters, including the Cr(VI). To reduce capital costs, there
have been major studies on the use of cheaper adsorbents which may be different
types of soils and clays. Removal of heavy metals with the use of soils is performed
based on the great adsorption capacity of the negatively charged parts of the soil and
the possibility of formation of complex molecules with organic molecules that are
located in the soil and thus resulting in the formation of oxides, hydroxides, and
other insoluble minerals. Clays show such properties, as a result of their chemical
and mechanical stability, large surface area, permanent negative voltage, and other
H. Memedi et al.