Oxidized eucalyptus charcoal: a renewable biosorbent for removing heavy metals from aqueous solutions

In this study, a comparison between charcoal produced from Eucalyptus urograndis modified and unmodified with HNO3 on the adsorption capacity of metals (Cu(II), Cd(II), and Ni(II)) in aqueous solutions was performed. The modification was performed using charcoal from the wood of a hybrid of Eucalyptus urophylla x Eucalyptus grandis (commonly referred to in Brazil as Eucalyptus urograndis). The charcoal was produced at a final temperature of 450 degrees C. Nitric acid was the oxidizing agent, employed at a concentration of 12.5% (v/v) and a reaction time of 3 h. The materials were characterized and compared using thermogravimetric analysis, thermogravimetric index, specific surface area analysis, scanning electron microscopy, elemental analysis, and point of zero charge. Studies of the process factors (contact time, mass, ideal pH), adsorption isotherms (Langmuir and Freundlich), and the thermodynamics of the process were also carried out. Treatment with nitric acid altered the elemental composition of charcoal, and functional groups, like carbonyl groups, were added to the surface, which caused a significant increase in total adsorption capacity (from 114.27 to 310.53 mg g(-1) in a solution with a mix of metals). The model that best fit the data was Langmuir, and the maximum removal of Cu(II) ions was 96%, and occurred at pH 5, at 318 K, with a dose of biosorbent equal to 0.4 g 50 mL(-1) of solution and equilibrium contact time of 30 min. Thermodynamic parameters suggested that adsorption occurred spontaneously and occurred through the ion exchange and electrostatic interaction mechanisms. In systems with the presence of more than one metal ion, the total adsorption capacity increased.

Automated summary

In this study, the effect of nitric acid treatment on the adsorption capacity of metals by charcoal was investigated, revealing that it enhanced the adsorption capacity significantly. The Langmuir model best described the adsorption isotherms, with a maximum removal of 96% of Cu(II) ions, suggesting that adsorption was spontaneous and occurred through ion exchange and electrostatic interaction mechanisms. Additionally, the presence of multiple metal ions in the solution increased the total adsorption capacity.