Adding value to marine macro-algae Laminaria digitata through its use in the separation and recovery of trivalent chromium ions from aqueous solution

Abstract

In this study, Laminaria seaweed was used in its protonated form as an effective biosorbent for chromium(III) removal from aqueous solutions. The effect of different operating conditions (pH, initial metal concentration and temperature) on the efficiency of the biosorption process was assessed. Biosorption was strongly dependent on the solution pH and less dependent on the temperature. The Cr(III) adsorption capacity of the seaweed increased with the pH. The maximum uptake capacity for Cr(III) was 42 mg g(-1) at pH 4, considering a maximum initial chromium concentration of 250 mg g(-1), at 25 degrees C. Langmuir and Freundlich models were able to fit well the experimental equilibrium data. The Langmuir equilibrium model parameters at pH = 4 and T = 25 degrees C are q(max) = 41 +/- 1 mg g(-1) and K-L = 0.31 +/- 0.04 L mg(-1). The adsorptive behavior of biosorbent particles was modeled using a batch reactor mass transfer kinetic model, which successfully predicts Cr(III) concentration profiles, with an average homogeneous diffusivity, D-h, of 0.13 x 10(-8) +/- 0.08 cm(2) s(-1). The biosorbent was characterized in terms of apparent density, real density, porosity, particle size and pore size distribution. The chemical characterization of the biosorbent was based on the determination of the main chemical constituents present in the structure of the biomass, and in the identification of active sites on the surface, by the Fourier Transform Infrared Spectroscopy (FTIR) technique. FTIR analysis of Laminaria digitata revealed the complex nature of the biomass, with different binding groups, such as carboxyl and sulfonic, which are responsible for the binding of the metals.