Removal of Cd (II) and Zn (II) ions from Aqueous Solutions using Carbonized and Functionalized Persea americana Root Stem Powder

The ability of carbonized and modified avocado (Persea americana) root stem powder (C-PA and M-PA) to remediate Cadmium (Cd (II)) and Zinc (Zn (II)) contamination in aqueous solution was studied by varying the carbonization temperature, particle size of the adsorbent, adsorption temperature, pH of the solution, contact time, adsorbent dose and adsorbate concentration. Scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) analyses were employed in characterizing both the C-PA and the M-PA. The removal efficiency of up to 86.9 and 90.8 was observed respectively for Cd (II) and Zn (II) at the optimal conditions. Florry-Huggins, Langmuir, Temkin, Dubinin–Radushkevich and Freundlich models were utilized in explaining the equilibrium isotherm of the sorption, and Florry-Huggins best described Zn (R2 = 0.999) while Cd was best described by Freundlich isotherm (R2 = 0.997). The kinetics of the sorption process were assessed and pseudo-first order was the best fit in describing Cd (II) uptake (R2 = 0.965), while Zn (II) was best fitted to the pseudo-second-order kinetics (R2 = 0.928). The thermodynamic variables revealed an endothermic sorption process for both adsorbates, with a reduction in spontaneity on temperature increase for Zn (II) while the reverse was observed for Cd (II). A single-stage adsorption experiment was performed using the optimal batch adsorption parameters and the result showed an increase in removal efficiency of up to 99.3 and 97.9 for Cd (II) and Zn (II) respectively.