Removal of Hexavalent Chromium from Aqueous Media using Mediterranean Posidonia oceanica biomass : Adsorption Studies and salt Competition Investigation

The biosorption of hexavelent chromium from saline solutions by Posidonia oceanica, a marine
biomass, was studied as a function of pH, initial chromium (VI) and salt (NaCl) concentrations in batch
system. The sorbent exhibited the maximal chromium (VI) uptake at pH 2 regardless of the presence of
increasing salt concentration. Equilibrium uptake increased with chromium (VI) concentration up to 250 mg/
l and decreased slightly in the presence of increasing salt concentrations of salt up to 50 g/l. The biomass
adsorbed 14.48 mg of metal per gram of biomass at 100 mg/l initial chromium concentration in the absence of
salt. When 50 g/l salt concentration was added to the solution, the value diminished to 11.49 mg/g under the
same conditions (i.e. a 20.6% decrease in the biosorption capacity). The equilibrium sorption data were
analyzed using Freundlich, Langmuir and Redlich-Peterson models. The Langmuir equation was the most
suitable adsorption model for describing the biosorption equilibrium data of chromium (VI) both in salt free
and loaded media. The pseudo-second-order type kinetic model depicted the biosorption kinetics accurately
at all chromium concentrations in absence and presence of increasing concentrations of salt.