____________________ Kinetics, Thermodynamics and Sorption Studies__________________
CHAPTER 4
KINETICS, THERMODYNAMICS AND
SORPTION STUDIES OF METAL IONS ON BIMETALLIC
INORGANIC CATION EXCHANGER
The tremendous increase in the use of heavy metals over the past few decades
has resulted in an increased flux of metallic substances into the environment. The heavy
metals are dangerous because they are non-degradable and therefore persistent.
Commonly encountered metals of concern include Pb2+, Hg2+, Bi3+, Cd2+, Cu2+, Zn2+,
Co2+ and Ni2+ etc. These metals are toxic both in their chemically combined forms and
in the elemental form. Hence safe and effective disposal of wastewater containing
heavy metals is always a challenge to industrialists and environmentalists, since cost-
effective treatment are not available.
The removal and recovery of toxic/heavy metals is an area of current interest. A
number of technologies have been developed for the efficient removal of toxic metal
ions from wastewater. Adsorption of pollutants on solid adsorbents is an effective
method for the removal of heavy metals from aqueous solution. The extend of
adsorption depends on the porosity and surface area of the adsorbent. The porous
structure plays a major role in the increase of adsorption rate. Synthetic inorganic
exchangers based on tetravalent metal acid salts possess an appreciable ion exchange
capacity as well as high selectivity for certain metal ions, metal ion selectivity is an
important criterion for choosing the exchanger for the removal of certain metal ions.
Adsorption is a process that occurs when a gas or liquid solute accumulates on
the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film
(adsorbate). Adsorption is operative in most natural, physical, chemical and biological
systems and is widely used in industrial applications. Adsorption is usually described
through isotherms, that is, functions which connect the amount of adsorbate on the
surface of adsorbent, with its pressure (if gas) or concentration (if liquid). For
describing the process of adsorption, Langmuir isotherm, Freundlich isotherm, BET
isotherm etc were used. In the present endeavour, we have studied Langmuir and
Freundlich isotherms in more detail.
129
,____________________ Kinetics, Thermodynamics and Sorption Studies__________________
To study the adsorption process in detail, determination of kinetic and
thermodynamic parameters is important. Kinetic and thermodynamic studies provide
information regarding the mechanism and feasibility of ion exchange process occuring on
the surface of the exchanger as well as the ability to predict correlation among
experimental results. From kinetic studies we can understand the order of reaction
occuring on the surface and calculate the reaction rate constant. Determination of
thermodynamic parameters like enthalpy change (∆H0), free energy change (∆G0) and
entropy change (∆S0) provide valuable information about the process of adsorption of
metal ions on the surface of the exchanger.
Some of the important features of zirconium based bimetallic cation exchangers
are that they possess good chemical and thermal and radiation stability. They have high
ion exchange capcity and the capacities are retained even at high temperatures. So we
select the newly synthesized zirconium bismuth molybdate (ZrBiMo) exchanger for the
studies of adsorption kinetics of metal ions. Physicochemical characterizations of
ZrBiMo reveal the crystalline nature and granular structure of the material (explained in
chapter 2). Granular structure provides increased surface area which in turn increases
the rate of adsorption process. From distribution studies it is found that ZrBiMo have
more selectivity towards Pb2+, Cu2+, Co2+ and Ni2+ ions in comparison with other metal
ions studied (Table 2.30). These are considered as highly toxic metal ions when they
reached in the environment. Hence we choose these metal ions for adsorption studies
and in this chapter, we explain the studies of kinetics, thermodynamics and sorption
characteristics of Pb2+, Cu2+, Co2+ and Ni2+ metal ions on the surface of ZrBiMo cation
exchanger and implicated the environmental applicability of the material in removing
these toxic metal ions from various industrial effluents.
4.1. EXPERIMENTAL
4.1.1 Preparation of stock solutions
Analytical grade metallic salts (Nice Chemicals) of required quantity were
dissolved in deionized water to prepare stock solution. The stock solutions are diluted
with deionized water to obtain solutions of various concentrations as and when
required. 0.1 N HCl and 0.1 N NaOH were used to adjust the pH of the solutions.
Industrial wastewaters collected from a local industry were used for adsorption studies.
130
, ____________________ Kinetics, Thermodynamics and Sorption Studies__________________
4.1.2. Sorption studies
The adsorption experiments were carried out in batch mode at ambient
temperatures. For this, 200 mg of the exchangers were agitated with 20 mL of metal ion
solution in a shaker at a speed of 150 rpm at room temperature. The concentration of
metal ions that remained in the solution, after being centrifuged was analysed by
complexometric titrations. In this study, the effects of several factors such as, pH,
concentration of metal ion solution, adsorbent doses, temperature and contact time were
examined.
4.1.3. Kinetics and thermodynamics of adsorption
The sorption kinetics describes the solute uptake rate which in turn governs the
residence time of a sorption reaction. It is one of the important characteristics in defining
the efficiency of a sorption process. The kinetic experiments were conducted in batch
mode. pH of the solution was adjusted to the value at which maximum sorption of
respective metal ions takesplace. Metal ion solution (20 mL of 0.01M) was shaken with
200 mg of the exchanger in stoppered conical flasks at desired temperatures (303, 313,
323 and 333 K) and at different time intervals with increments of 10 min (10, 20, 30, -----
120 min). The supernatant liquid was removed immediately after each prescribed time
interval and the metal ion concentration was evaluated by complexometric titrations169.
The metal ion concentrations after adsorption at 0.5 min and at infinite time (24 hours)
were also determined. All experiments were carried out in duplicate. The results obtained
from this study were utilized to evaluate kinetic and thermodynamic parameters like
enthalpy change (∆H0), free energy change (∆G0) and entropy change (∆S0).
4.1.4. Adsorption isotherm studies
For adsorption isotherm studies, 20 mL metal ion solution of different
concentrations (0.005, 0.01, 0.015 and 0.02M) was equilibrated for a specific period of
time with 200 mg of the exchanger in stoppered conical flasks at desired temperatures
(303, 313, 323 and 333 K). The supernatant liquid was removed immediately and metal
ion concentration was evaluated by EDTA titrations169.
4.1.5. Desorption studies
Desorption studies were carried out to analyse the mechanism of adsorption and
recovery of the adsorbate and adsorbent. The regeneration of the adsorbent may make
the treatment process economical. The supernatant was separated after centrifugation
131
CHAPTER 4
KINETICS, THERMODYNAMICS AND
SORPTION STUDIES OF METAL IONS ON BIMETALLIC
INORGANIC CATION EXCHANGER
The tremendous increase in the use of heavy metals over the past few decades
has resulted in an increased flux of metallic substances into the environment. The heavy
metals are dangerous because they are non-degradable and therefore persistent.
Commonly encountered metals of concern include Pb2+, Hg2+, Bi3+, Cd2+, Cu2+, Zn2+,
Co2+ and Ni2+ etc. These metals are toxic both in their chemically combined forms and
in the elemental form. Hence safe and effective disposal of wastewater containing
heavy metals is always a challenge to industrialists and environmentalists, since cost-
effective treatment are not available.
The removal and recovery of toxic/heavy metals is an area of current interest. A
number of technologies have been developed for the efficient removal of toxic metal
ions from wastewater. Adsorption of pollutants on solid adsorbents is an effective
method for the removal of heavy metals from aqueous solution. The extend of
adsorption depends on the porosity and surface area of the adsorbent. The porous
structure plays a major role in the increase of adsorption rate. Synthetic inorganic
exchangers based on tetravalent metal acid salts possess an appreciable ion exchange
capacity as well as high selectivity for certain metal ions, metal ion selectivity is an
important criterion for choosing the exchanger for the removal of certain metal ions.
Adsorption is a process that occurs when a gas or liquid solute accumulates on
the surface of a solid or a liquid (adsorbent), forming a molecular or atomic film
(adsorbate). Adsorption is operative in most natural, physical, chemical and biological
systems and is widely used in industrial applications. Adsorption is usually described
through isotherms, that is, functions which connect the amount of adsorbate on the
surface of adsorbent, with its pressure (if gas) or concentration (if liquid). For
describing the process of adsorption, Langmuir isotherm, Freundlich isotherm, BET
isotherm etc were used. In the present endeavour, we have studied Langmuir and
Freundlich isotherms in more detail.
129
,____________________ Kinetics, Thermodynamics and Sorption Studies__________________
To study the adsorption process in detail, determination of kinetic and
thermodynamic parameters is important. Kinetic and thermodynamic studies provide
information regarding the mechanism and feasibility of ion exchange process occuring on
the surface of the exchanger as well as the ability to predict correlation among
experimental results. From kinetic studies we can understand the order of reaction
occuring on the surface and calculate the reaction rate constant. Determination of
thermodynamic parameters like enthalpy change (∆H0), free energy change (∆G0) and
entropy change (∆S0) provide valuable information about the process of adsorption of
metal ions on the surface of the exchanger.
Some of the important features of zirconium based bimetallic cation exchangers
are that they possess good chemical and thermal and radiation stability. They have high
ion exchange capcity and the capacities are retained even at high temperatures. So we
select the newly synthesized zirconium bismuth molybdate (ZrBiMo) exchanger for the
studies of adsorption kinetics of metal ions. Physicochemical characterizations of
ZrBiMo reveal the crystalline nature and granular structure of the material (explained in
chapter 2). Granular structure provides increased surface area which in turn increases
the rate of adsorption process. From distribution studies it is found that ZrBiMo have
more selectivity towards Pb2+, Cu2+, Co2+ and Ni2+ ions in comparison with other metal
ions studied (Table 2.30). These are considered as highly toxic metal ions when they
reached in the environment. Hence we choose these metal ions for adsorption studies
and in this chapter, we explain the studies of kinetics, thermodynamics and sorption
characteristics of Pb2+, Cu2+, Co2+ and Ni2+ metal ions on the surface of ZrBiMo cation
exchanger and implicated the environmental applicability of the material in removing
these toxic metal ions from various industrial effluents.
4.1. EXPERIMENTAL
4.1.1 Preparation of stock solutions
Analytical grade metallic salts (Nice Chemicals) of required quantity were
dissolved in deionized water to prepare stock solution. The stock solutions are diluted
with deionized water to obtain solutions of various concentrations as and when
required. 0.1 N HCl and 0.1 N NaOH were used to adjust the pH of the solutions.
Industrial wastewaters collected from a local industry were used for adsorption studies.
130
, ____________________ Kinetics, Thermodynamics and Sorption Studies__________________
4.1.2. Sorption studies
The adsorption experiments were carried out in batch mode at ambient
temperatures. For this, 200 mg of the exchangers were agitated with 20 mL of metal ion
solution in a shaker at a speed of 150 rpm at room temperature. The concentration of
metal ions that remained in the solution, after being centrifuged was analysed by
complexometric titrations. In this study, the effects of several factors such as, pH,
concentration of metal ion solution, adsorbent doses, temperature and contact time were
examined.
4.1.3. Kinetics and thermodynamics of adsorption
The sorption kinetics describes the solute uptake rate which in turn governs the
residence time of a sorption reaction. It is one of the important characteristics in defining
the efficiency of a sorption process. The kinetic experiments were conducted in batch
mode. pH of the solution was adjusted to the value at which maximum sorption of
respective metal ions takesplace. Metal ion solution (20 mL of 0.01M) was shaken with
200 mg of the exchanger in stoppered conical flasks at desired temperatures (303, 313,
323 and 333 K) and at different time intervals with increments of 10 min (10, 20, 30, -----
120 min). The supernatant liquid was removed immediately after each prescribed time
interval and the metal ion concentration was evaluated by complexometric titrations169.
The metal ion concentrations after adsorption at 0.5 min and at infinite time (24 hours)
were also determined. All experiments were carried out in duplicate. The results obtained
from this study were utilized to evaluate kinetic and thermodynamic parameters like
enthalpy change (∆H0), free energy change (∆G0) and entropy change (∆S0).
4.1.4. Adsorption isotherm studies
For adsorption isotherm studies, 20 mL metal ion solution of different
concentrations (0.005, 0.01, 0.015 and 0.02M) was equilibrated for a specific period of
time with 200 mg of the exchanger in stoppered conical flasks at desired temperatures
(303, 313, 323 and 333 K). The supernatant liquid was removed immediately and metal
ion concentration was evaluated by EDTA titrations169.
4.1.5. Desorption studies
Desorption studies were carried out to analyse the mechanism of adsorption and
recovery of the adsorbate and adsorbent. The regeneration of the adsorbent may make
the treatment process economical. The supernatant was separated after centrifugation
131
