1.2 Adsorption Technique
3
1.2 Adsorption Technique
Adsorption has been reported to be an inexpensive and efficient method for the
elimination of many water contaminants [5]. Adsorption is a mechanism whereby
the molecules of a material are attracted and maintained on a solid surface. Adsorption
is called mass transfer process, in that, a part from the liquid phase is moved to the
solid phase. Adsorption can take place on the material’s external layer and then in the
macrospores, mesopores, micropores and submicropores relative to the surface area
of the micropores and submicropores; therefore, the surface area of the macro and
mesopores is small, and the quantity of substance adsorbed there is generally deemed
insignificant. Adsorption can be grouped into two classifications, such as physical
adsorption (physisorption) and chemical adsorption (chemisorption), based on the
nature of force occurring between adsorbent molecule (metal ion) and adsorbent.
Physical adsorption (physisorption) derives from the action of weak forces
between molecules, also regarded as adsorption by van der Waals. The energy of
contact between the adsorbent and the adsorbent has the same magnitude but is
generally higher than the adsorbing condensing energy. Therefore, no activation
energy is required. In this instance, adsorption is influenced by the low temperature.
Physisorption, consequently, declines with rising temperatures. In physical adsorption, an equilibrium between the adsorbent and the fluid phase is formed, leading
to multilayer adsorption. Physical adsorption is unspecific because of low binding
forces acting between molecules. The adsorbed molecule on the solid surface is
not assigned to a position but is able to move across the layer. By essence physical
adsorption is practically reversible. In this circumstance, the adsorbed species are
chemically similar with those in the fluid phase, so that adsorption and eventual
desorption do not influence the chemical properties of the fluid; therefore, it is not
unique in nature [5].
Chemical adsorption (chemisorption) is also dependent at electrostatic force
in chemisorption; the interaction forces exiting between adsorbent and adsorbent
molecules are probably to be the same as chemical bonds. Thus, the chemisorption energy is regarded as chemical processes. It may be exothermic or endothermic
mechanisms, from very small to very large energy magnitudes. The essential stage
of chemical adsorption also requires significant energy for activation, which implies
that the actual equilibrium can be gradually reached. Similarly, a spontaneous system
demands a negative free energy (IFE) value, because when adsorbed, the adsorbate’s translational mobility is reduced [4]. In particular, metal ions’ adsorption to
an adsorbent is considered to occur via the following steps.
(a) Movement of metal ions from bulk solution to the adsorbent surface commonly
referred to as diffusion.
(b) Movement of metal ions through the pores.
(c) Engagement of metal ions on the internal surface of pores with accessible sites.
3
1.2 Adsorption Technique
Adsorption has been reported to be an inexpensive and efficient method for the
elimination of many water contaminants [5]. Adsorption is a mechanism whereby
the molecules of a material are attracted and maintained on a solid surface. Adsorption
is called mass transfer process, in that, a part from the liquid phase is moved to the
solid phase. Adsorption can take place on the material’s external layer and then in the
macrospores, mesopores, micropores and submicropores relative to the surface area
of the micropores and submicropores; therefore, the surface area of the macro and
mesopores is small, and the quantity of substance adsorbed there is generally deemed
insignificant. Adsorption can be grouped into two classifications, such as physical
adsorption (physisorption) and chemical adsorption (chemisorption), based on the
nature of force occurring between adsorbent molecule (metal ion) and adsorbent.
Physical adsorption (physisorption) derives from the action of weak forces
between molecules, also regarded as adsorption by van der Waals. The energy of
contact between the adsorbent and the adsorbent has the same magnitude but is
generally higher than the adsorbing condensing energy. Therefore, no activation
energy is required. In this instance, adsorption is influenced by the low temperature.
Physisorption, consequently, declines with rising temperatures. In physical adsorption, an equilibrium between the adsorbent and the fluid phase is formed, leading
to multilayer adsorption. Physical adsorption is unspecific because of low binding
forces acting between molecules. The adsorbed molecule on the solid surface is
not assigned to a position but is able to move across the layer. By essence physical
adsorption is practically reversible. In this circumstance, the adsorbed species are
chemically similar with those in the fluid phase, so that adsorption and eventual
desorption do not influence the chemical properties of the fluid; therefore, it is not
unique in nature [5].
Chemical adsorption (chemisorption) is also dependent at electrostatic force
in chemisorption; the interaction forces exiting between adsorbent and adsorbent
molecules are probably to be the same as chemical bonds. Thus, the chemisorption energy is regarded as chemical processes. It may be exothermic or endothermic
mechanisms, from very small to very large energy magnitudes. The essential stage
of chemical adsorption also requires significant energy for activation, which implies
that the actual equilibrium can be gradually reached. Similarly, a spontaneous system
demands a negative free energy (IFE) value, because when adsorbed, the adsorbate’s translational mobility is reduced [4]. In particular, metal ions’ adsorption to
an adsorbent is considered to occur via the following steps.
(a) Movement of metal ions from bulk solution to the adsorbent surface commonly
referred to as diffusion.
(b) Movement of metal ions through the pores.
(c) Engagement of metal ions on the internal surface of pores with accessible sites.