Lead biosorption from aqueous solution by raw and chemically modified green fresh water algae Scenedesmus obliquus

Biosorption of lead (Pb) from aqueous solution by biomass of green algae, (Scenedesmus obliquus), was investigated as a function of initial solution pH, contact time, and temperature. Additionally, the effect of CaCl2 pretreatment on the Pb uptake capacity of biomass has been investigated. The Langmuir isotherm analysis revealed that the modified biomass (Q(max)=207.2, 1/b=19. 10) has a great uptake capacity and higher affinity towards the Pb metal than the raw biomass (Q(max)=112.0, 1/b=56. 91). The absorption process was complied with Freundlich isotherm (R-2=0.9938 and 0.9629). The Freundlich isotherm analysis showed that the modified biomass (K-f=78.10, 1/n=0.6019) has a great uptake capacity and higher affinity toward Pb than the raw biomass (K-f=22.35, 1/n=0.7680). The mean biosorption energy calculated from Dubinin-Radushkevich plot (8.84 and 10.44kJ/mol) suggested chemical biosorption. FTIR spectra indicated the presence of different functional groups, such as amino, carboxyl, hydroxyl, and carbonyl groups, on the cell wall of the S. obliquus biomass. The change in the band intensity and frequency indicate the involvement of these functional groups in Pb binding. Also, the severe decrease in all band intensity indicates that the CaCl2 increases the biosorption capacity of the S. obliquus biomass. The obtained results proved that treatment with CaCl2 has increased the uptake capacity of the S. obliquus biomass and could be used as a potential biosorbent for the removal of Pb from aqueous solutions.