4.8 Results and Discussion
81
of heavy metals. At pH value beyond 6, insoluble cadmium hydroxide and lead
hydroxide begin to precipitate from the solution, inducing a decline in the percentage
reduction of metal ions. The influence of pH can also be described in terms of the
pH Pzc of adsorbent. The zero-charge point is the point at which the acidic or basic
functional surface groups no longer participate to the solution’s pH value. The pH Pzc
was observed to be about 4.5. Under pH 4.5, the outer layer is charged positively, and
metal ion linkage appears to be weak because of the electrostatic repulsion. Raising
the pH beyond pH P zc, the GXCS layer becomes negatively charged, thus increasing
the adsorption of metal ions.
4.8.3 Influence of Adsorbent Dose
The observational study revealed that the level of extraction is significantly affected
by a change in the number of adsorbents. Additionally, a significant rise in the
percentage removal was confirmed for both metal ions, by increasing the dose from
1.5 to 4.5 g/L. This reported phenomenon could be based on the fact that adequate
adsorption sites were able to facilitate cadmium and lead ion complexation. Raising
the adsorbent dose above 4.5 g/L did not produce such a relevant changes in the
removal efficiency, and this improvement could be attributed to the attachment of
nearly all metal ions to GXCS and the balance between the adsorbent ions and those
kept unadsorbed in the solution [23] (Fig. 4.2).
40
50
60
70
80
90
100
1
2
3
4
5
6
7
Removal, %
Adsorbent dossage (g/l)
cadmium
lead
Fig. 4.2 Influence of adsorbent dosage on per cent removal of cadmium and lead by GXCS (conditions: initial ion conc: 40 mg/L; contact time: 120 min; solution pH: cadmium = 6.0, lead = 5.0;
temperature: 25 °C)
81
of heavy metals. At pH value beyond 6, insoluble cadmium hydroxide and lead
hydroxide begin to precipitate from the solution, inducing a decline in the percentage
reduction of metal ions. The influence of pH can also be described in terms of the
pH Pzc of adsorbent. The zero-charge point is the point at which the acidic or basic
functional surface groups no longer participate to the solution’s pH value. The pH Pzc
was observed to be about 4.5. Under pH 4.5, the outer layer is charged positively, and
metal ion linkage appears to be weak because of the electrostatic repulsion. Raising
the pH beyond pH P zc, the GXCS layer becomes negatively charged, thus increasing
the adsorption of metal ions.
4.8.3 Influence of Adsorbent Dose
The observational study revealed that the level of extraction is significantly affected
by a change in the number of adsorbents. Additionally, a significant rise in the
percentage removal was confirmed for both metal ions, by increasing the dose from
1.5 to 4.5 g/L. This reported phenomenon could be based on the fact that adequate
adsorption sites were able to facilitate cadmium and lead ion complexation. Raising
the adsorbent dose above 4.5 g/L did not produce such a relevant changes in the
removal efficiency, and this improvement could be attributed to the attachment of
nearly all metal ions to GXCS and the balance between the adsorbent ions and those
kept unadsorbed in the solution [23] (Fig. 4.2).
40
50
60
70
80
90
100
1
2
3
4
5
6
7
Removal, %
Adsorbent dossage (g/l)
cadmium
lead
Fig. 4.2 Influence of adsorbent dosage on per cent removal of cadmium and lead by GXCS (conditions: initial ion conc: 40 mg/L; contact time: 120 min; solution pH: cadmium = 6.0, lead = 5.0;
temperature: 25 °C)