Adsorption of lithium, rubidium, cesium, thallium, and lead onto activated charcoal: adsorption selectivity, kinetics, isotherms, and decontamination potential.

INTRODUCTION

The adsorption capacity of activated charcoal was systematically evaluated for five metal ions, lead, thallium, cesium, rubidium and lithium, with particular emphasis on elucidating the underlying adsorption mechanisms and ion selectivity patterns.

METHODS

The surface structure of activated charcoal was characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed desorption mass spectrometry to identify potential functional groups involved in the adsorption of metal ions. The concentration of metal ions was measured by inductively coupled plasma-mass spectrometer. The effects of adsorption time, pH, and ion concentration were systematically studied. Adsorption kinetics were fitted to the pseudo-first-order and pseudo-second-order models to elucidate the dominant mechanism, representing physisorption and chemisorption, respectively. Adsorption isotherms were fitted to the Langmuir and Freundlich models to evaluate the adsorption capacity and behavior of activated charcoal.

RESULTS

The surface of activated charcoal contains potential adsorption functional groups, including carboxyl, phenolic hydroxyl, carbonyl, and anhydride. The material exhibits adsorption of lead, thallium, cesium and rubidium ions, while showing no adsorption for lithium ions. Adsorption capacity increased with both pH (ranging from 2 to 6) and metal ion concentration. All adsorption processes followed the pseudo-second-order kinetic model, suggesting that chemisorption is the predominant adsorption mechanism. Adsorption isotherms showed lead, cesium and rubidium ions best fit the Langmuir model, while thallium followed the Freundlich model. Both Langmuir and Freundlich models indicated favorable adsorption under experimental conditions. The experimental adsorption capacity decreased in the order: lead (8.8 mg/g) > thallium (2.7 mg/g) > cesium (1.0 mg/g) > rubidium (0.7 mg/g) > lithium (0.0 mg/g).

DISCUSSION: This study found that the adsorption capacity of activated charcoal for different metal ions is influenced by factors such as pH and metal ion concentration. As pH increased, the adsorption efficiency improved, suggesting that the highly acidic environment in the stomach (pH ≈ 1.2) may limit its effectiveness in decontamination. Additionally, the study revealed that, under a chemisorption dominated mechanism, the adsorption capacity of activated charcoal follows a consistent pattern with the relative atomic masses of the five metal ions.

CONCLUSIONS

This study systematically evaluates the adsorption of five metal ions by activated charcoal, revealing that adsorption capacity is influenced by pH, ion concentration, and atomic mass, with chemisorption as the dominant mechanism, providing valuable insights for its application in metal ion poisoning treatment.