Application of Sustainable and Low-Cost Sludge-Based Adsorbents …
39
2.4 Adsorption Chemical Kinetics Modelling
The efficiency of the adsorption process describing the mass transfer and chemical
reactions is controlled by the kinetic models. Various kinetic models have been used
and different systems use different models, but the Lagergren’s rate equations [64]
for the sorption of a solute from a liquid solution are commonly used. In many cases,
the first-order equation of Lagergren does not fit well to the whole range of contact
time and is generally applicable over the initial stage of the adsorption processes [75].
In recent years, pseudo-second-order rate law has been considerable as one of the
most appropriate models. Linear isothermal regression was widely used to determine
the most fitted model throughout the years, and the method of least squares has been
frequently used for finding the parameters of the models. However, transformations of
nonlinear isotherm equations have implicitly altered their error structure and variance
by assumptions of standard least squares.
Several error analysis methods such as the coefficient of determination, the sum of
the errors squared, a hybrid error function, Marquardt’s per cent standard deviation,
the average relative error and the sum of absolute errors have been used to determine
the best-fitting isotherm [6, 47]. The linear regression and chi-square analysis of three
isotherms, Langmuir, Freundlich and Redlich–Peterson, were compared by Ho. In
this study, chi-square (χ
2 ) tests of the two Langmuir isotherms were similar on the
same abscissa and ordinate, whereas the Redlich–Peterson and Freundlich isotherm
exhibited identical and lower χ
2 values than Langmuir.
2.5 Adsorbent Precursors
In recent years, preparation and application of non-conventional adsorbents using
precursors such as natural materials, biosorbents and waste materials from industry
and agriculture with lower cost and high efficiency have gained importance. It is
suggested as convenient alternative treatment for the discolouration of wastewaters
from the textile industry [16, 24, 36, 61]. Industrial wastes represented as unused
resources are to be turned into a useful resource for the colour removal of various
dyes. The tannery industry is also inserted into this context. Numerous research works
are carried out using waste materials in order to avert an increasing toxic threat to
the environment and to streamline the waste disposal techniques.
2.5.1 Fly Ash
One of the industrial by-products available in abundance in the world is fly ash. It
is a waste substance from thermal power plants and steel plants. The use of fly ash
for removal of dyes from aqueous solution was first reported by Khare et al. [62].
The effect of different concentrations and pH on Victoria blue dye was studied under
39
2.4 Adsorption Chemical Kinetics Modelling
The efficiency of the adsorption process describing the mass transfer and chemical
reactions is controlled by the kinetic models. Various kinetic models have been used
and different systems use different models, but the Lagergren’s rate equations [64]
for the sorption of a solute from a liquid solution are commonly used. In many cases,
the first-order equation of Lagergren does not fit well to the whole range of contact
time and is generally applicable over the initial stage of the adsorption processes [75].
In recent years, pseudo-second-order rate law has been considerable as one of the
most appropriate models. Linear isothermal regression was widely used to determine
the most fitted model throughout the years, and the method of least squares has been
frequently used for finding the parameters of the models. However, transformations of
nonlinear isotherm equations have implicitly altered their error structure and variance
by assumptions of standard least squares.
Several error analysis methods such as the coefficient of determination, the sum of
the errors squared, a hybrid error function, Marquardt’s per cent standard deviation,
the average relative error and the sum of absolute errors have been used to determine
the best-fitting isotherm [6, 47]. The linear regression and chi-square analysis of three
isotherms, Langmuir, Freundlich and Redlich–Peterson, were compared by Ho. In
this study, chi-square (χ
2 ) tests of the two Langmuir isotherms were similar on the
same abscissa and ordinate, whereas the Redlich–Peterson and Freundlich isotherm
exhibited identical and lower χ
2 values than Langmuir.
2.5 Adsorbent Precursors
In recent years, preparation and application of non-conventional adsorbents using
precursors such as natural materials, biosorbents and waste materials from industry
and agriculture with lower cost and high efficiency have gained importance. It is
suggested as convenient alternative treatment for the discolouration of wastewaters
from the textile industry [16, 24, 36, 61]. Industrial wastes represented as unused
resources are to be turned into a useful resource for the colour removal of various
dyes. The tannery industry is also inserted into this context. Numerous research works
are carried out using waste materials in order to avert an increasing toxic threat to
the environment and to streamline the waste disposal techniques.
2.5.1 Fly Ash
One of the industrial by-products available in abundance in the world is fly ash. It
is a waste substance from thermal power plants and steel plants. The use of fly ash
for removal of dyes from aqueous solution was first reported by Khare et al. [62].
The effect of different concentrations and pH on Victoria blue dye was studied under