88
4 Investigation into the Adsorption of Cadmium and Lead …
both metal ions was all negative and this means that the reaction is random and satisfactory. The positive value of H
o suggests the adsorption system’s is endothermic in
nature. The positive values of H
o while adsorbing these metal ions GXCS confirm
the elevated randomness at the solid–solution interface. This result coincides with
the outcome provided by Liu et al. [29].
4.10.3 Outcome of Kinetic Investigation
The results collected from the investigation performed were used to study the adsorption of cadmium kinetics and lead ion on GXCS. The kinetic data were designed using
the pseudo-first-order and pseudo-second-order model. Previous studies have proven
that the pseudo-second-order kinetic model makes the adsorption data better suited
[2]. Table 4.3 displays the parameter values for the pseudo-first and second-order
kinetic models, and it was found that the coefficient of correlation for the linear plot
of t/q t against t from the pseudo-second-order rate law provided the best support
for both metal ions in comparison with the coefficient of correlation of the pseudofirst-order kinetic model derived from the linear plot of log (q e − q t ) against t. The
chi-square test (λ
2 ) of data collection was introduced to further analyse the kinetic
results. The values of 2 for the pseudo-first-order kinetic model and pseudo-secondorder kinetic model were indicated in Table 4.3 as being comparable. Consequently,
the q e measured value by evaluating from the pseudo-first-order kinetic model and
experimental values were significantly different. In the case of the second-order
pseudo-model, the q e(Cal) values are very much in line with the experimental results.
This implies that the adsorption of cadmium and lead ions to GXCS is a pseudosecond-order mechanism model, and this model is assumed that the rate limiting
step could be chemical adsorption or chemisorption requiring valence forces via the
exchange of electrons between adsorbents (metal ions) and adsorbents (GXCS) [12].
4.10.4 Outcome of Desorption/Regeneration Investigation
Figure 4.8 depicts the influence of utilizing specific eluents such as HCl, HNO3
and EDTA to desorb used GXCS at a concentration range of 0.01–1.0 M and 3 h
of desorption time. Optimum desorption of 98.94% of HCl, 95.32% of EDTA and
76.56% of HNO 3 was achieved at a concentration of 0.5 M for cadmium ion packed
GXCS and a total desorption of 97.5% of HCl, 92.4% of EDTA and 65% of HNO 3
was recorded at the same concentration. This finding is important as it can assist
to uncover the correct eluent and the concentration to be introduced to the used
adsorbent in the desorption medium.
Efforts were made to assess the reuse and regeneration of metal ions from its
used adsorbent. Five phases of adsorption/desorption experiments were conducted,
and it was noticed that the adsorption potential of GXCS for cadmium and lead ions
4 Investigation into the Adsorption of Cadmium and Lead …
both metal ions was all negative and this means that the reaction is random and satisfactory. The positive value of H
o suggests the adsorption system’s is endothermic in
nature. The positive values of H
o while adsorbing these metal ions GXCS confirm
the elevated randomness at the solid–solution interface. This result coincides with
the outcome provided by Liu et al. [29].
4.10.3 Outcome of Kinetic Investigation
The results collected from the investigation performed were used to study the adsorption of cadmium kinetics and lead ion on GXCS. The kinetic data were designed using
the pseudo-first-order and pseudo-second-order model. Previous studies have proven
that the pseudo-second-order kinetic model makes the adsorption data better suited
[2]. Table 4.3 displays the parameter values for the pseudo-first and second-order
kinetic models, and it was found that the coefficient of correlation for the linear plot
of t/q t against t from the pseudo-second-order rate law provided the best support
for both metal ions in comparison with the coefficient of correlation of the pseudofirst-order kinetic model derived from the linear plot of log (q e − q t ) against t. The
chi-square test (λ
2 ) of data collection was introduced to further analyse the kinetic
results. The values of 2 for the pseudo-first-order kinetic model and pseudo-secondorder kinetic model were indicated in Table 4.3 as being comparable. Consequently,
the q e measured value by evaluating from the pseudo-first-order kinetic model and
experimental values were significantly different. In the case of the second-order
pseudo-model, the q e(Cal) values are very much in line with the experimental results.
This implies that the adsorption of cadmium and lead ions to GXCS is a pseudosecond-order mechanism model, and this model is assumed that the rate limiting
step could be chemical adsorption or chemisorption requiring valence forces via the
exchange of electrons between adsorbents (metal ions) and adsorbents (GXCS) [12].
4.10.4 Outcome of Desorption/Regeneration Investigation
Figure 4.8 depicts the influence of utilizing specific eluents such as HCl, HNO3
and EDTA to desorb used GXCS at a concentration range of 0.01–1.0 M and 3 h
of desorption time. Optimum desorption of 98.94% of HCl, 95.32% of EDTA and
76.56% of HNO 3 was achieved at a concentration of 0.5 M for cadmium ion packed
GXCS and a total desorption of 97.5% of HCl, 92.4% of EDTA and 65% of HNO 3
was recorded at the same concentration. This finding is important as it can assist
to uncover the correct eluent and the concentration to be introduced to the used
adsorbent in the desorption medium.
Efforts were made to assess the reuse and regeneration of metal ions from its
used adsorbent. Five phases of adsorption/desorption experiments were conducted,
and it was noticed that the adsorption potential of GXCS for cadmium and lead ions