Assessment of the effectiveness of water hyacinth (E. crassipes) in the biosorption of heavy metals from Aluminium extruding company effluents

Abstract

Biosorption technique was used to assess the effectiveness of water hyacinth in the removal of heavy metal from effluents obtained from an Aluminium extruding company. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques were used to characterize the water hyacinth materials before and after adsorption. A batch experiment was set up using water hyacinth (E. crassipes) ash as absorbent. The effects of contact time, absorbent dose, pH and temperature on the heavy metal removal efficiency were determined. The experimental data were analysed by the Langmuir, Freundlich and Temkin models of adsorption. The FTIR results showed a reduction in the intensity of the adsorption bands for all the metal ions. The optimal percentage removal of the metal occurred at 30 minutes except Cd which had highest percentage removal at 20 minutes while optimal pH was at 6.0 except Pb which had its optimal removal at pH 4.0. Increase in biosorbent dosage increased the percentage removal of the metal ions with Zn (96% at 1.0 g) having the highest percentage removal of the five metal ions studied. The results revealed that Langmuir and Temkin Isotherms were the best model for the metal ions adsorption onto water hyacinth. Langmuir model had a better fit for Fe (R² = 0.78), Ni (R² = 0.82) and Pb (R² = 0.78), while Temkin model fitted best for Cd (R² = 0.92) and Zn (R² = 0.96). The E. crassipes, therefore, could serve as effective, low-cost and environmentally friendly adsorbents.