Removal of Cd(II) and Pb(II) from synthetic wastewater using Rosa damascena waste as a biosorbent: An insight into adsorption mechanisms, kinetics, and thermodynamic studies

Due to their toxicity to public health, the presence of inorganic pollutants in the aquatic environment have become a global concern. This work investigates the technical feasibility of R. damascena waste as a biosorbent (RWB) in batch studies for the removal of Cd(II) and Pb(II) from synthetic wastewater. The biomass waste is abundantly available from rose oil industries in Lahore (Pakistan). To improve its treatment performance for metals removal, the biomass waste is pretreated with H2SO4 and NaOH, respectively. To understand the roles of functional groups on the RWB during biosorption, Fourier Transform infrared (FT-IR) spectroscopy and scanning electron microscope (SEM) analyses were used to compare its surface area before and after adsorption. At the same initial metal concentration of 25 mg/L, it was found that the chemically modified R. damascena could remove 95% and 91% of Pb(II) and Cd(II), respectively, under the optimum conditions: pH 6.5, reaction time: 2 h, 10 g/L of dose, and 120 rpm of shaking speed. Its metal adsorption capacities were 24.9 and 24.8 mg/g for Pb(II) and Cd(II), respectively. The Langmuir isotherm was applicable to simulate the adsorption of both target metals, while the pseudo-second order fitted well their kinetics. The characterization results implied the roles of certain functional groups of the biosorbent as electron donors. This indicates that H-bonding was involved in the chemisorption of target metals by the biosorbent. In spite of their encouraging findings, treated effluents were still unable to meet the required discharge limits of 0.05 and 0.005 mg/L for Pb(II) and Cd(II), respectively, mandated by local legislation. This reveals that another subsequent treatment using biological process such as activated sludge is required to complement their removal from wastewater samples. Overall, this work reveals the applicability of R. damascena waste as a biosorbent for heavy metal removal.