Adsorption of Pb(II) from aqueous solution using keratin waste – hide waste: Equilibrium, kinetic and thermodynamic modeling studies

• Leather waste without tanning was used as the adsorbent.
• A novel simple method of preparing adsorbent using urea was applied.
• The adsorption was controlled by chemical ion-exchange process.
• HWUS and HWSU had more amino functional groups than HWS.
• Adsorption of Pb(II) was well fitted to Langmuir isotherm.

This study probed and compared the adsorption capacities of hide waste (HW) biosorbents, namely steamed (HWS), modified by urea (HWUS), and both-first steamed then urea-modified hide waste (HWSU). The three biosorbents were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Boehm’s titration and X-ray photoelectron spectroscopy (XPS). The XRD data of the samples indicated that the crystallinity of HWS became ordered after adsorbing Pb(II). Based on the XPS, FTIR and Boehm’s titration results, HWS had more acidic functional groups and less amino functional groups than HWUS and HWSU. Batch adsorption experiments were performed to evaluate the adsorption properties of the biosorbents toward Pb(II), which indicated that the adsorption capacity of HWS increased after modified by urea. The adsorption was demonstrated to be strongly influenced by the pH, and the optimum pH was 5.5. Adsorption kinetics followed the pseudo-second-order model, and the equilibrium data were well described by Langmuir isotherm than the other equations. The Dubinin–Radushkevich (D–R) isotherm indicated a process of chemical adsorption. Cation exchange, surface complexation and electrostatic attraction could be the main adsorption mechanisms for Pb(II) adsorption onto the biosorbents. Thermodynamics showed that the adsorption was an exothermic process.