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 marinebiomass, was studied as a function of ph, initial chromium (vi) and salt (nacl) concentrations in batchsystem. the sorbent exhibited the maximal chromium (vi) uptake at ph 2 regardless of the presence ofincreasing 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 biomassadsorbed 14.48 mg of metal per gram of biomass at 100 mg/l initial chromium concentration in the absence ofsalt. when 50 g/l salt concentration was added to the solution, the value diminished to 11.49 mg/g under thesame conditions (i.e. a 20.6% decrease in the biosorption capacity). the equilibrium sorption data wereanalyzed using freundlich, langmuir and redlich-peterson models. the langmuir equation was the mostsuitable adsorption model for describing the biosorption equilibrium data of chromium (vi) both in salt freeand loaded media. the pseudo-second-order type kinetic model depicted the biosorption kinetics accuratelyat all chromium concentrations in absence and presence of increasing concentrations of salt.