BIOSORPTION OF Pb2+, Cd2+, & Ni2+ FROM WATERS BY ...

Table 3.6. Competitive biosorption of Pb 2+ + Cd 2+ + Ni 2+ by Scenedesmus protuberans
(10.0 mL solution of different mixed-metal ion concentration, solution of 6.0,
and sorption time as 60 min)
% Sorption
Pb 2+
Cd 2+
Ni 2+
Initial
concentration of
Pb 2+ + Cd 2+ + Ni 2+
(mg/L) Single Mixed Single Mixed Single Mixed
10.0 98.6 ±0.1 100 ± 0.0 84.6 ± 0.2 100.0 ±0.0 95.0 ± 0.1 87.5 ± 0.2
50.0 99.6 ± 0.2 99.8 ± 0.2 73.2 ± 0.0 40.4 ± 0.6 48.5 ± 0.4 28.7 ± 0.3
100.0 99.5 ± 0.5 94.8 ± 0.6 44.8 ± 1.1 13.0 ± 1.2 31.5 ± 0.8 10.1 ± 1.2
3.5. Successive Loading
Successive loading of Pb 2+ , Cd 2+ , and Ni 2+ by Dunaliella salina, Oocystis sp.
Porphyridium cruentum, Scenedesmus protuberans for initial metal ion concentration as
10.0 mg/L was examined as explained in section 2.4. The results are shown in Figure
3.20-3.23. Dunaliella salina has an ability to continue to biosorb Pb 2+ , Cd 2+ ions from
the solution in higher than Ni 2+ ions after five successive runs performed. However, in
the third cycle, biosorption of Pb 2+ by Dunaliella salina is lowered.
Repetitive loading of Pb 2+ and Cd 2+ on the biosorbents Oocystis sp. and
Scenedesmus protuberans does not appear to be affected significantly even after five
successive loadings. On the contrary, biosorption of Ni 2+ by Oocystis sp. starts to
decline at the fifth successive loading, whereas that of Ni 2+ by Scenedesmus protuberans
does at the fourth cycle.
In the case of Porphyridium cruentum, at the first cycles, Cd 2+ , and Ni 2+ ions are
removed in lower amount, then at the later runs, Cd 2+ , and Ni 2+ removal increases. This
behaviour can be attributed to the presence of Na + ions present in the biomass of
Porphyridium cruentum. In Pb 2+ case, the biosorbent continues to hold most of its
original uptake capacity over five cycles of use in the biosorption of Pb 2+ (removes the
ions almost totally for five cycles). To confirm the lower sorption of Cd 2+ and Ni 2+ ions
by Porhyridium cruentum, the experiments were continued at 10.0 - 100.0 mg/L metal
ion concentrations for 10 successive loadings. The results are shown in Figure 3.24-3.25.
It can be seen that, after eight successive runs were applied the sorption of Cd 2+ ions
levelled off. This situation can also be seen for the sorption of Ni 2+ ions at fourth
successive runs passed. If the concentration of the metal ions was increased, the sorbed
52