Biosorption of C.I. Reactive Black 5 from aqueous solution using acid-treated biomass of brown seaweed Laminaria sp.

Abstract

The biosorption of C.I. Reactive Black 5 (RB5) from aqueous solution, using the brown seaweed, Laminaria sp., was investigated in both batch and column modes of operation. Protonation of the native Laminaria biomass, with 0.1 M HCl, considerably improved its RB5 biosorption capacity. Evidence from FT-IR spectra confirmed the participation of amine groups in the biosorption of RB5 and the mechanism was proposed to be electrostatic interaction between the positively charged amine groups and negatively charged RB5. At various initial RB5 concentrations (50–200 mg/l), batch sorption equilibrium was reached within 3 h, followed by slow attainment of equilibrium, and the kinetic data obtained were interpreted in terms of the pseudo-second order model. Biosorption isotherm experiments, under different pH and temperature conditions, revealed that decreasing the pH and increasing the temperature favored biosorption. The Langmuir, Freundlich and Redlich–Peterson models were used to describe the isotherm data; of which the Freundlich model described the isotherm data with high correlation coefficients and low percentage error values. According to the Langmuir model, the maximum RB5 uptake of 101.5 mg/g was observed at pH 1 and temperature of 40 °C. Various thermodynamic parameters, such as Δ G°, Δ H° and Δ S°, were calculated, which indicated that the present system was spontaneous and endothermic process. A 0.01 M NaOH solution successfully eluted all dye from the RB5-loaded Laminaria biomass. The feasibility of the brown seaweed for the continuous removal of RB5 from aqueous solution was examined in an up-flow packed column (1 cm ID and 12 cm height). With a bed height, flow rate and initial RB5 concentration at 10 cm, 1 ml/min and 50 mg/l, respectively, the Laminaria biomass exhibited an RB5 uptake and removal efficiency of 41.9 mg/g and 72.7%, respectively. The column was successfully eluted using 0.01 M NaOH, with an elution efficiency of 97.7%.