Adsorption Behavior of Pb(II), Cd(II), and Zn(II) onto Agave Bagasse, Characterization, and Mechanism

Abstract

Biosorption is an alternative procedure to remove metal ions from aqueous media using agricultural waste. In this work, the adsorption capacity and removal efficiency of agave bagasse (AB) toward Pb(II), Cd(II), and Zn(II) were analyzed. Parameters such as equilibrium pH, particle size, AB dosage, time, and initial metal ion concentration were discussed. The results showed that pH 5.5, 0.4 g (<250 μm), and only 15 min of contact assured conditions for maximum adsorption capacity. The kinetic studies were fitted to the pseudo-second-order model, whereas the isotherms showed good agreement with the Langmuir model. AB has a higher affinity for Pb(II) over Cd(II) and Zn(II), and the maximum adsorption capacities were 93.14, 28.50, and 24.66 mg g-1, respectively. The results of the characterization evidenced two adsorption mechanisms. Scanning electron microscopy and X-ray diffraction displayed adsorption via the ion exchange mechanism by releasing Ca(II). The 13C cross-polarization mode with magic-angle spinning nuclear magnetic resonance analysis demonstrated a complexation mechanism by cellulose, hemicellulose, and lignin groups with Pb(II) and Cd(II), whereas the complexation is mainly observed by cellulose groups for Zn(II). AB is a good alternative for the removal of metals without prior thermal or chemical treatment, with rapid kinetics, suitable adsorption capacity, and high removal efficiency contributing to waste management.