Removal of hexavalent chromium from aqueous media using mediterranean Posidonia oceanica biomass: adsorption studies and salt competition investigation

ABSTRACT

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