Chapter 3
(mg/g) and removal % which were determined using Eq. (2.1-2.2). Finally, the performance of PS and BSAC were studied for various solution concentrations (50-300 mg/L), by choosing all other parameters from results obtained with above mentioned preliminary adsorption studies. Further details with respect to the results obtained from the three sets of adsorption experiments are presented below.
3.3.1 Effect of contact time
Fig. 3.2 presents the variation in % adsorption and metal uptake (mg/g) with contact time for BSAC and PS. Corresponding choice of other parameters include adsorbent dosage, pH and Ni (II) concentration as 0.02 g/L, 5-6 and 50 mg/L respectively. It can be observed that the minimum time required to achieve equilibrium (i.e., maximum adsorption) is 300 and 90
0 50 100 150 200 250 300 350 400 40
50 60 70
Per ce nt a g e re mo v a l
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92
2 4 6 8 10
55 60 65 70
(PS) (BSAC)
Percentage removal
Initial pH
Fig. 3.3: Effect of pH on Nickel (II) removal using BSAC and PS adsorbents. Other experimental conditions were Co = 50 mg/L, T = 25 oC, RPM = 200 and V = 50 mL.
minutes for PS and BSAC respectively. For these cases, the maximal removal % was estimated at 67.12 and 67.34% respectively. Corresponding metal uptake (mg/g) for the adsorbents were 83.9 and 84.17 mg/g respectively. The observations are in good agreement with those available in the literature (Lalhruaitluanga et al., 2011; Hameed et al., 2009).
3.3.2 Effect of pH
Fig. 3.3 presents the effect of pH on the adsorbent performance of BSAC and PS.
Corresponding choice of other parameters include adsorbent dosage, Ni (II) solution concentration and contact time are 0.02 g/L, 50 mg/L and 90 (BSAC), 300 (PS) min respectively. It can be observed in these figures that adsorption and metal uptake curves reach a maximum at a certain pH and eventually reduce at higher pH values. For the PS, the % removal and adsorption capacity increased to 69.82% and 87.27 mg/g with an increase in pH
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from 2-5. Similarly, for the BSAC the % removal and metal uptake increased to 86.67 mg/g and 69.28% respectively. It can be observed in these figures that adsorption and metal uptake curves reach a maximum at a certain initial pH and eventually reduce at higher initial pH values. These observations are in agreement with that presented in the literature for PS and BSAC adsorbents (Lalhruaitluanga et al., 2011; Hameed et al., 2009; McKay et al., 2008).
The enhancement in Ni (II) adsorption with increasing initial pH is due to the competence of both H+ and metal ion to get adsorbed at lower initial pH which reduced metal ion binding to the adsorbent surface at lower pH. At a higher initial pH, the sorbent surface develops more negative charges and hence can strongly attract more number of metal ions. A further increase in initial pH enables the formation of anionic hydroxide complexes which reduce the availability of the metal ion in the solution and restrict the adsorptive capacity (McLean and Bledsoe (1992)).
3.3.3 Effect of Dosage
The effect of dosage variation on Ni (II) removal using developed adsorbents is presented in Fig.3.4. Corresponding choice of other parameters include pH, Ni (II) solution concentration.
The contact time are 5, 50 mg/L and 90 (BSAC), 300 (PS) min respectively. It can be observed that with an increase in dosage from 0.02 to 0.15 g/L, the maximum metal uptake and % removals are 21.3175, 23.185 mg/g and 85.27, 92.74 for PS and BSAC respectively.
The enhancement in adsorption for higher dosages is due to the availability of more active sites for binding the metal to the adsorbent surfaces. Similar results are reported in the literature (Lalhruaitluanga et al., 2011; Hameed et al., 2009).
Chapter 3
94
0.00 0.04 0.08 0.12 0.16
70 80 90
PS BSAC
Percentage removal
Dosage (g)
Fig. 3.4: Effect of adsorbent dosage on Ni (II) removal efficiency using BSAC and PS adsorbents. Other experimental conditions were Co = 50 mg/L, T = 25 oC, RPM = 200
and V = 50 mL.
3.3.4 Ni (II) adsorption characteristics of AC using synthetic ELP solutions
The evaluation of Ni (II) adsorption characteristics using synthetic ELP solutions was carried out using commercial activated carbon adsorbent. Based on the preliminary batch adsorption experiments conducted for the adsorption of Ni (II) from aqueous solutions using BSAC adsorbent, the optimal adsorption parameters correspond to a pH of 5, equilibrium time of 90 min and dosage of 2 g/L. Using activated carbon, the optimal set of adsorption parameters for Ni (II) adsorption from synthetic electroless plating solutions correspond to a pH of 10-11, equilibrium time of 120 min and dosage of 4 g/L. While Ni (II) adsorption characteristics were studied for BSAC adsorbent and aqueous solutions in the concentration range of 50-300 mg/L, the Ni (II) adsorption studies with synthetic ELP solutions were carried out in the concentration range of 50-500 mg/L.
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Fig. 3.5 (a) and (b) present the variation in metal capacity and removal efficiency respectively with a variation in solution concentration for both ELP and aqueous solutions. It can be observed in Fig 3.5 (a) that the metal uptake varied from 16.84-91.59 mg/g for aqueous solutions in the Ni (II) concentration range of 50-300 mg/L. However, significantly lower metal uptake variations exist (5.56-17.75 mg/g) for the synthetic Ni (II) ELP solutions in the concentration range of 50-500 mg/L. The most relevant literature data for comparison purpose refers to the Ni (II) adsorption data for banana pith based AC adsorbent and electroplating solutions. The reported metal uptake in the literature refers to 11.42 mg/g for a solution concentration of 5000 × 10-6M (28 mg/L). Thus, it is apparent that significantly lower Ni (II) metal uptake values have been obtained for the synthetic ELP solutions in compared to those measured for AC adsorbents for both aqueous (this work) and electroplating (Low et al., 1995) solutions. This indicates that the solution chemistry plays an important role in altering the capacity characteristics of the AC adsorbents.
0 100 200 300 400 500
0 20 40 60 80 100
Metal uptake on sorbent (mg/g)