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

CHAPTER 4
CONCLUSION
It has been shown that Dunaliella salina, Oocystis sp., Porphyridium cruentum,
and Scenedesmus protuberans can be utilized for the sorption of Pb 2+ , Cd 2+ , and Ni 2+
ions prior to flame atomic absorption spectrometric determination. In the first part of the
study, the characterization of Dunaliella salina, Oocystis sp., Porphyridium cruentum,
and Scenedesmus protuberans was investigated with SEM images, FTIR spectra,
elemental analysis, and TGA decomposition curves of algae. SEM images show that
each alga has different unit structures and sizes. It can be derived from the FTIR spectra
that the functional groups present in the algae are responsible for the metal uptake.
Percentage concentrations of C, H, N, and S was determined by elemental analyzer and
each alga was found to have different elemental composition. The thermal stability of
the algae was investigated through the TGA plots and Porphyridium cruentum was
found to be the most stable one among the others.
Optimization of the biosorption parameters, such as solution pH, initial metal ion
concentration, shaking time, biomass amount were carried out to elucidate the sorption
characteristics of the algae. Solution pH was adjusted to 6.0 as a compromised point
which is both sufficiently higher than the isoelectronic point of the algal cells that
guarantees the surface is negatively charged and also reasonably lower than the pHs
where the metal hydroxides start to be formed. It was demonstrated that the primary
sorption mechanism is the electrostatic attraction between the negatively charged
functional groups on the surface of the biomass and the positively (+2) charged metal
ions in the solution.
Uptake of metal ions is affected from the shaking time and it can be said that all
algae had a very fast kinetics towards the metal ions. Even 5 min have been shown to be
adequate to reach equilibrium under the optimized conditions; however, a shaking time
of 60 min was applied in all studies to be on the safe side.
Among the biomasses investigated, Dunaliella salina has shown the highest
sorption capacity for all the metal ions. It was followed by Oocystis sp., Scenedesmus
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