Removal of Cd(II) and Pb(II) from aqueous solution using Ziziphus lotus leaves as a potential biosorbent

Ziziphus lotus is a wild plant that has recently become appreciated mainly due to the antioxidant and nutrient-rich properties of its fruits. The powder of the inedible leaves was investigated in this research in batch mode for its capacity to remove cadmium(II) and lead(II) ions as an eco-friendly and cost-effective biosorbent. Leaves powder revealed the highest uptake rate at pH = 8 and pH = 7 for Cd(II) and Pb(II), consecutively. The best metal adsorption rate is obtained with a temperature ranging from 25 degrees C to 30 degrees C, a contact time of 90 min, an initial ionic concentration of 100 mg/L, and a biosorbent dosage ranging from 3.5 to 5 g/L. The experimental kinetic data of the biosorption process for both heavy metal ions were fitted by the pseudo-second-order model. The equilibrium data fitted very well to the Langmuir model and Temkin model. The maximum monolayer biosorption capacities were 70.78 and 80.75 mg/g for Cd(II) and Pb(II), respectively. The main chemical groups which are involved in the trapping of Cd(II) and Pb(II) and which have been revealed by Fourier-transform infrared spectral analysis are: O-C, O=C, H-O, H-C, and N-C. The biosorption was endothermic (Delta H degrees = 7.33 kJ/mol for Cd(II), and 5.33 kJ/mol for Pb(II)). The reac-tion was accompanied by a decrease in entropy (Delta S degrees = -19.87 J/K center dot mol for Cd(II), and -8.38 J/K center dot mol for Pb(II)). When the temperature increases from 293 to 333 K, the Gibbs energy (Delta G degrees) increased, indicating that biosorption was less feasible at higher temperatures. The present research con-firms that Z. lotus leaves could be exploited as a low-cost and an effective biosorbent for the elimination of Cd(II) and Pb(II) ions from aqueous solution.