PublicationWater Advanced Treatment & Environmental Research Laboratory

Adsorption of Pb²+ and Zn²+ from aqueous solutions using dried powder of cactus Opuntia: characterization, adsorption capacity and kinetics
First author
Yirga Weldu Abrha
Yongtae Ahn, Homin Kye, Youmi Jung, Yeojoon Yoon, Tae-Mun Hwang
Corresponding author
Joon-Wun Kang
Joon-Wun Kang
Dried powder of the cactus Opuntia was used as an adsorbent to remove Pb²+ and Zn²+ from aqueous solution. The characteristics of the adsorbent were studied using Brunauer–Emmett–Teller (BET), point of zero charge (pHpzc), Fourier transform infrared spectroscopy (FTIR),and energy dispersive spectroscopy (EDS) analyses. Adsorption efficiency experiments were conducted on single-metal aqueous systems, including variations in dose, contact time, initial adsorbate concentration, initial solution pH, and temperature. The maximum removal efficiencies of Pb²+and Zn²+ were found to be 90.6% and 37.6%, respectively, with adsorbent doses of 0.5 and 2.0 g. The maximum amount adsorbed onto Opuntia adsorbent for Pb²+ (119.0 mg/g) was found to be higher than that of Zn²+ (32.3 mg/g) at the 300 and 200 mg/L initial concentrations of Pb²+and Zn²+ ions, respectively. A rapid rise in binding efficiency was observed with increasing pH up to 4, and Pb²+ ions adsorbed preferentially compared to Zn²+. The pseudo-second-order and Elovich models best fit the experimental data on the adsorption of Pb²+and Zn²+ onto Opuntia powder. The energy dispersive spectroscopy (EDS) analysis was employed to confirm the adsorption process. In isotherm studies, the maximum adsorption capacity (qmax) was calculated to be 62.9 mg/g for Pb²+ and 21.6 mg/g for Zn²+. The adsorption data for both Pb²+ and Zn²+obeyed the Freundlich model. A thermodynamic study showed that the adsorption process was spontaneous and endothermic. The results of the present study indicate that dried Opuntia powder as low-cost adsorbent could be useful and effective for the removal of heavy metals, especially in developing countries.