Application of sugarcane leaves as biomass in the removal of cadmium(II), lead(II) and zinc(II) ions from polluted water

Abstract

Here, we present the removal of cadmium(II), lead(II) and zinc(II) ions, by sugarcane (Saccharum spontaneum) leaves. Biomass characterisation was performed with Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray and X-ray diffractometry. The effects of parameters such as solution pH, initial metal ion concentration and contact time were investigated. To understand the adsorption process, data were fitted into models such as the pseudo-first order, pseudo-second order, Weber–Morris, Langmuir, Freundlich and Dubinin–Radushkevich (D–R). The surface of the adsorbent was oval and irregular in shape, with scattered adsorptive sites. Carbon and oxygen were the main element present in the adsorbent, claiming about 59% and 38% of the total elemental compositions, respectively. Optimum pH for lead and zinc ions was 5, while 6 was chosen for cadmium ions. Adsorption increased with time and eventually plateaued after 5 h for lead and 4 h for cadmium and zinc ions. Metal uptake increased with increase in initial metal ion concentration up to 250 mg/L. Adsorption data fitted best to the Langmuir isotherm, with maximum sorption capacity, qmax, obtained as 142.86, 156.25 and 166.67 mg/g for the removal of cadmium, lead and zinc, respectively. The pseudo-second-order model provided the best fit for the kinetic data (R2 of > 0.95), indicating that the sorption process was controlled by chemisorption mechanism. Information from Freundlich and D–R models signified that the uptake of the three metal ions was by physisorption and that ion-exchange mechanism was also involved in zinc adsorption.