Comparative studies on the olive stone activated carbon adsorption of Zn²⁺, Ni²⁺, and Cd²⁺ from synthetic wastewater

Abstract

The adsorption of a group of heavy metals namely, Zn²⁺, Ni²⁺, and Cd²⁺ onto olive stones activated carbon (OSAC) was carried out in this work. The effects of different reaction parameters, such as the adsorbent dosage, contact time, shaking speed, and initial pH, on pollutant removal efficiency were investigated. Adsorption of Zn²⁺, Ni²⁺, and Cd²⁺ was effectively explained by Langmuir and Freundlich isotherms. OSAC efficiently removed 99.03% Zn²⁺, 97.34% Ni²⁺, and 94.88% Cd²⁺ at pH 5 and shaking speed 200 rpm. Surface characteristics of the prepared AC were examined by pore structure analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy. The Brunauer-Emmett-Teller surface area, total pore volume and average pore diameter of the prepared AC were 886.72 m²/g, 0.507 cm/g, and 4.22 nm, respectively. The equilibrium data of the adsorption were fitted well to the Langmuir and the highest value of adsorption capacity (Q) on the OSAC was found for Zn²⁺ 11.14 mg/g, followed by Ni²⁺ 8.42 mg/g and Cd²⁺ 7.80 mg/g. A pseudo-second-order model sufficiently described the adsorption kinetics, which indicated that the adsorption process was controlled by chemisorption. The results revealed that the OSAC has the potential to be used as a low-cost adsorbent for the treatment of wastewaters contaminated with heavy metals.

Keywords:

• Olive stone
• Activated carbon
• Adsorption
• Isotherm
• Heavy metals
• Kinetics

Acknowledgements

The authors wish to acknowledge the Universiti Sains Malaysia (USM) for its financial support under the USM and TWAS Fellowship scheme and RU-PRGS grant scheme (No. 8045048) and acknowledge Ministry of Higher Education, Malaysia for providing LRGS Grant No. (203/PKT/670006) and (03-01-05-SF0502) to conduct this study.