Kinetics of Hg adsorption onto noncrystalline Al hydroxide as influenced by low-molecular-weight organic ligands

ABSTRACT

This study was conducted to investigate the kinetics of Hg adsorption by noncrystalline Al hydroxide as influenced by various pH conditions and cysteine (cys), glycine (gly), and citric acid (cit), which have different structures and functionalities, as low-molecular-weight organic ligands using the GEOCHEM-PC software. The influence of these organic ligands on the kinetics of Hg adsorption varied according to their concentration, structure, and functionality and pH. The adsorption of Hg followed multiple first order kinetics with initial rapid adsorption, followed by slow adsorption. Cysteine suppressed or enhanced Hg adsorption, depending on pH and its concentration. Glycine and citric acid exerted suppressing and enhancing effects, respectively, with the exception of at pH 4.5 and at lower concentrations, at which no influence was observed as compared to the control. Two mechanisms were thought to mediate the adsorption of Hg(II); specific surface complexation in the control, cysteine and glycine systems, and ligand exchange in the citric acid system. The Hg adsorption at all levels of organic ligands decreased with increasing pH, with the exception of at the higher concentration of cysteine, at which the reverse trend was observed. The influence of organic ligands on the dynamics of Hg in the freshwater environment merits further study.

KEYWORDS:

• Hg(II)
• organic ligands
• speciation
• adsorption
• Al(OH)₃

Acknowledgements

This study was supported by the Kangwon National University (KNU) and the Research Center of the Surface Soil Resources inventory and integration (SSORii) at KNU, funded by the GAIA Project of the Korea Environmental and Industry Technology Institute (KEITI). Also, the authors extend their heartfelt thanks to the late Huang PM, who was formerly a professor at the University of Saskatchewan, Saskatoon, Canada, for his valuable advice.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Kangwon National University (KNU), the Research Center of the Surface Soil Resources inventory and integration (SSORii) at KNU and the GAIA Project of the Korea Environmental and Industry Technology Institute (KEITI).