14
1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …
studies have been under way to establish the impact of pH on environmentally friendly
adsorbent adsorption of metal ion.
Tumin et al. [14] performed a research on the impact of pH on Cu(II) reduction
by activated carbon at a pH range of 2–8. From the investigation, it was confirmed
that Cu(II) absorption enhanced significantly from pH 2–6, additional rise in pH led
to a reduction in adsorption capacity. This finding was ascribed to the conclusion
that the layer of the adsorbent is enclosed by hydrogen ions at lower pH values,
thus restricting Cu(II) ions from reaching the adsorbent’s active sites, and as the ph
rises moderately to pH 6, more negatively charged surface will become accessible,
enabling better elimination of Cu(II) ion. Enhancing the pH value beyond pH 6 led
to reduced adsorption power, and it was recorded that this finding was attributed to
the presence of Cu(II) ion precipitation.
Popuri et al. [126] explored the role of pH on Ni(II) and Cu(II) ion adsorption by
chitosan-coated polyvinyl chloride beads, at pH levels of 1–6. The findings suggested
that maximal Cu(II) adsorption occurred at pH 4, whereas higher Ni(II) adsorption
occurred at pH 5. The authors ascribed this finding to high concentrations of hydrogen
ions at reduced pH value, which contend for active site together with Cu(II) and Ni(II)
ions.
Gyananath and Balhal [131] analysed the role of pH on Pb(II) reduction from
aqueous solutions by adsorption on chitosan beads at a pH range of 2–6. The adsorption improved with the solution rising in pH. This finding was attributed to the
assumption that the amine groups in the beads are protonated at low pH, resulting in
electrostatic repulsion of Pb(II) ion. Consequently, a competition between protons
and lead(II) ions for adsorption site exists and hence, the adsorption potential reduced.
1.4.2 Effect of Temperature
Temperature has been seen to influence adsorption ability among the design variables
which are commonly examined in the literature. The process is called endothermic
when the adsorption capacity rises with temperature, and the process is called
exothermic when adsorption capacity declines with temperature. The thermodynamic
variables focus on providing the basic parameters for consequent engineering assessment of the actual adsorption of the adsorbents and ideally often offer additional
perspectives into the process of adsorption required for further process modification
and optimization techniques [5, 135]. Han et al. [136] suggested that the growing
adsorption potential of the adsorbent with temperature is due to pore enhancement
and/or adsorbent surface activation.
Kannamba et al. [125] examined the impact temperature has on the adsorption
potential of modified chitosan for Cu(II) ion. The researchers concluded a rise in
adsorption potential as temperature rises from 20 to 50 °C. This increase was related
to the endothermic nature of the binding mechanism. Payne and Abdel-Fattah [52]
explored the influence of temperature by activated carbon and zeolite on the adsorption of leads. Activated carbon adsorption efficiency was unchanged by temperature
1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …
studies have been under way to establish the impact of pH on environmentally friendly
adsorbent adsorption of metal ion.
Tumin et al. [14] performed a research on the impact of pH on Cu(II) reduction
by activated carbon at a pH range of 2–8. From the investigation, it was confirmed
that Cu(II) absorption enhanced significantly from pH 2–6, additional rise in pH led
to a reduction in adsorption capacity. This finding was ascribed to the conclusion
that the layer of the adsorbent is enclosed by hydrogen ions at lower pH values,
thus restricting Cu(II) ions from reaching the adsorbent’s active sites, and as the ph
rises moderately to pH 6, more negatively charged surface will become accessible,
enabling better elimination of Cu(II) ion. Enhancing the pH value beyond pH 6 led
to reduced adsorption power, and it was recorded that this finding was attributed to
the presence of Cu(II) ion precipitation.
Popuri et al. [126] explored the role of pH on Ni(II) and Cu(II) ion adsorption by
chitosan-coated polyvinyl chloride beads, at pH levels of 1–6. The findings suggested
that maximal Cu(II) adsorption occurred at pH 4, whereas higher Ni(II) adsorption
occurred at pH 5. The authors ascribed this finding to high concentrations of hydrogen
ions at reduced pH value, which contend for active site together with Cu(II) and Ni(II)
ions.
Gyananath and Balhal [131] analysed the role of pH on Pb(II) reduction from
aqueous solutions by adsorption on chitosan beads at a pH range of 2–6. The adsorption improved with the solution rising in pH. This finding was attributed to the
assumption that the amine groups in the beads are protonated at low pH, resulting in
electrostatic repulsion of Pb(II) ion. Consequently, a competition between protons
and lead(II) ions for adsorption site exists and hence, the adsorption potential reduced.
1.4.2 Effect of Temperature
Temperature has been seen to influence adsorption ability among the design variables
which are commonly examined in the literature. The process is called endothermic
when the adsorption capacity rises with temperature, and the process is called
exothermic when adsorption capacity declines with temperature. The thermodynamic
variables focus on providing the basic parameters for consequent engineering assessment of the actual adsorption of the adsorbents and ideally often offer additional
perspectives into the process of adsorption required for further process modification
and optimization techniques [5, 135]. Han et al. [136] suggested that the growing
adsorption potential of the adsorbent with temperature is due to pore enhancement
and/or adsorbent surface activation.
Kannamba et al. [125] examined the impact temperature has on the adsorption
potential of modified chitosan for Cu(II) ion. The researchers concluded a rise in
adsorption potential as temperature rises from 20 to 50 °C. This increase was related
to the endothermic nature of the binding mechanism. Payne and Abdel-Fattah [52]
explored the influence of temperature by activated carbon and zeolite on the adsorption of leads. Activated carbon adsorption efficiency was unchanged by temperature