Comparative study of the adsorption capacity of lead (II) ions onto bean husk and fish scale from aqueous solution

The present study compared the adsorption capacity of Pb (II) ions from aqueous solution onto biopolymer materials (BPMs): (bean husk (BH) and fish scale (FS)). Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were used to characterize the BPMs. The optimal conditions of the variables: pH, adsorbent dosage, initial metal concentration, contact time and temperature were ascertained. Experimental data were applied to the Langmuir, Freundlich and Temkin sorption isotherms using the linear equations form. The optimal removal of Pb (II) ions with BH and FS was obtained at pH 7.0 and 6.0, and 0.2 g adsorbent dosage each, respectively. The removal of Pb (II) ions fitted the pseudo-second order kinetic model well for the materials. Equilibrium Langmuir isotherm, which indicated a heterogeneous process, gave a better conformity than the other models used for BH while the Temkin isotherm gave better conformity for FS. The FS reached equilibrium faster (at about 30 min) compared to BH (at about 60 min); however, the processes are both spontaneous and endothermic. The BPMs gave about 90% removal of Pb (II) ions at the optimum dosage when used for textile wastewater. The BPMs, therefore, can be used as effective, low-cost and environmentally friendly adsorbents.