Evaluation of kinetic and thermodynamic parameters in adsorption of lead (Pb²⁺) and chromium (Cr³⁺) by chemically modified macadamia (Macadamia integrifolia)

Abstract

This study aimed to analyze the efficiency of in natura and chemically modified with sodium hydroxide macadamia mesocarp as alternative adsorbents for removal of Pb²⁺ and Cr³⁺ from aqueous medium. The effect of chemical modification on the in natura macadamia mesocarp with respect to chemical structure and morphological feature were verified by Fourier transform infrared spectroscopy, scanning electronic microscopy, and zero point charge. The best adsorption occurred when pH ranged from 4.0 to 5.0. The adsorbent–adsorbate equilibrium time was found to be at 200 min and followed the pseudo-second-order kinetic model. The maximum adsorption capacity of the modified mesocarp for Pb²⁺ and Cr³⁺ was found to be 91.40 and 81.63 mg g⁻¹, respectively. The thermodynamic parameters indicated an increase of the system spontaneity after the modification, corroborated by the negative values of Gibbs’ energy. Besides greater adsorption, the modified material also had greater ion desorption, approximately 94% for Pb²⁺ and 70% for Cr³⁺, and may be reutilized as a retention filter for metals in the future.

Keywords:

• Biosorption
• Heavy metals
• Macadamia integrifolia
• Modified chemically

Acknowledgments

This study was supported by the UNIPAR and UNIOESTE. The authors would like to thank CNPq (National Council for Scientific and Technological Development) and Araucária Foundation for the financial support and fellowships.