Adsorption of copper (Cu²⁺) from aqueous solution using date palm trunk fibre: isotherms and kinetics

Abstract

In this work, date palm trunk (DPT) fibre was investigated for the eviction of copper ions (Cu²⁺) from aqueous solution. The surface chemistry of the DPT adsorbent was characterized through Fourier transform infrared spectroscopy and X-ray powder diffraction. The specific surface area and the average crystalline size of the DPT fibre adsorbent were measured as 2.104 m² g⁻¹ and 320 nm, respectively. Equilibrium adsorption was achieved at 150 min and results reflected significantly higher adsorption of Cu²⁺ onto DPT fibre at pH 5 (6 mg g⁻¹, 12%) than at pH 2–4 (1–4 mg g⁻¹, 1–7%). The adsorption data revealed maximum removal (25.4 mg g⁻¹) at the adsorbent dose of 5 g L⁻¹. Significantly, removal (34 mg g⁻¹) was observed with particles 75 μm and Cu²⁺ removal was significantly higher (6–23 mg g⁻¹) with increasing Cu²⁺ concentration from 20 to 100 mg L⁻¹. Adsorption kinetics data were modelled using pseudo-first-order and pseudo-second-order kinetics. The behaviour and the nature of Cu²⁺ adsorption were analysed by employing the Langmuir, Freundlich, Harkins–Jura (H–J) and Dubinin–Radushkevich (D–R) isotherm models. The results reflect that the adsorption isotherm model fitted the experimental data in the following order: Langmuir (R², 0.9933) > H–J (R², 0.9869) > Freundlich (R², 0.9768) > D–R (R², 0.8827) with monolayer Cu²⁺ adsorption. The experimental data were best explained by a Langmuir isotherm model and pseudo-second-order kinetics with R² = 0.9933 and 0.9905, respectively, and q_max of 25.25 mg g⁻¹ with chemisorption (E = 14.59 kJ mol⁻¹). The homogeneity of the adsorbent surface functional groups makes DPT suited for sequestering toxic Cu²⁺ from wastewater. Suitable physical, chemical and physicochemical surface modifications can further improve the adsorption capabilities of DPT adsorbents.

Keywords:

• Adsorption
• Copper
• DPT fibre
• Kinetics
• Isotherm models

Acknowledgements

“This project was funded by the National Plan for Science, Technology and Innovation (MAARIFAH), King Abdulaziz City for Science and Technology, Kingdom of Saudi Arabia, Award Number (11-WAT1875-02)”.