Ethylenediaminetetraacetic acid (EDTA) functionalized silica spheres were used to remove metal ions from aqueous solutions. The adsorption kinetics of Cu 2+ , Zn 2+ , and Cd 2+ (60 mg•L −1 , pH 5.5) were fitted to the pseudosecond order model. Adsorption equilibria were reached within 20 min, indicating that chemisorption may be the limiting step in the adsorption process. Adsorption isotherms were analyzed with nonlinear models by considering the ERRSQ error function and the determination coefficient R 2 . The data with monoion solutions (10 mg•L −1 to 300 mg•L −1 ) were tested with Langmuir, Freundlich, and Redlich−Peterson isotherm models. The best fit was found with the Langmuir model, and maximum adsorption capacities followed the order: Cu 2+ > Zn 2+ > Cd 2+ . Breakthrough curves were obtained using filled columns. The adsorbed ions were quantitatively recovered on elution with hydrogen chloride (0.10 M). After three adsorption−recovery cycles, the metal ions could still be recovered almost quantitatively, which demonstrates the good performance of the EDTA-functionalized silica spheres.
This review discussed the last 10 years progress in the use of lignocellulosic materials chemically modified as low-cost biosorbents. Thus, the chemical modifications, such as chemical pretreatment, oxidation, as well as the grafting of carboxyl groups, amines, amides, etc., on lignocellulosic fibers, that aim to increase the number of adsorption sites and maximize toxic metal ion adsorption capacity have been addressed. The literature presents results that indicated performances of biosorbents equal to or even higher than conventional methods and adsorbents. Many efforts have been concentrated on the improvements of these biosorbents through chemical modifications. However, some difficulties still exist, including the discharge of colored organic compounds resulting from the pretreatments and the development of fast, clean, and low-cost synthesis of selective and multifunctional adsorbents. Thus, the challenge for future research is to find solutions to these difficulties in order to finally make lignocellulosics biosorbents that can replace conventional adsorbent materials.
This work investigates copper, nickel and zinc ion biosorption in single- and multi-component systems in a fixed-bed column using green coconut shells (CS). Approximately 85% of biosorbents are in a particle size ranging from 0.25 to 2 mm. Operational parameters selected include a flow rate of 200 mL min-1 and a bed height of 100 cm, which were selected for a shorter execution time and good adsorption capacity. Empty-bed contact time and Thomas models were applied, showing a good fit with the experimental data. The column adsorption capacity increased after the green CS powder was treated in a column with NaOH at a concentration of 0.1 mol L-1. The highest values of adsorption capacities founded were 0.69, 0.45 and 0.39 mmol L-1 for Cu(II), Ni(II) and Zn(Il), respectively, using green CS treated inside a column with NaOH of 0.1 M. The pH and chemical oxygen demand were monitored in the treatment solution and indicated that the adjustment of these parameters is necessary before disposal of these solutions. A study of desorption using an acid solution was carried out for recovery of metal ions.
Buriti fibers were subjected to an alkaline pre-treatment and tested as an adsorbent to investigate the adsorption of copper, cadmium, lead and nickel in mono- and multi-element aqueous solutions, the results showed an increase in the adsorption capacity compared to the unmodified Buriti fiber. The effects of pH, adsorbent mass, agitation rate and initial metal ions concentration on the efficiency of the adsorption process were studied using a fractional 2(4-1) factorial design, and the results showed that all four parameters influenced metal adsorption differently. Fourier transform infrared spectrometry and X-ray fluorescence analysis were used to identify the groups that participated in the adsorption process and suggest its mechanisms and they indicated the probable mechanisms involved in the adsorption process are mainly ion exchange. Kinetic and thermodynamic equilibrium parameters were determined. The adsorption kinetics were adjusted to the homogeneous diffusion model. The adsorption equilibrium was reached in 30 min for Cu(2+) and Pb(2+), 20 min for Ni(2+) and instantaneously for Cd(2+). The results showed a significant difference was found in the competitiveness for the adsorption sites. A mathematical model was used to simulate the breakthrough curves in multi-element column adsorption considering the influences of external mass transfer and intraparticle diffusion resistance.
The
adsorption of aqueous solutions of BTEX (benzene, B; toluene,
T; ethyl benzene, E; and xylenes, X) on hydrophobically modified zeolite
was investigated. Multicomponent kinetics and equilibrium studies
were carried out using a batch system. Furthermore, a mathematical
model was studied that considers the mass transfer kinetics in a fixed-bed
adsorption system. The influences of external mass transfer as well
as the constant adsorption equilibrium and intraparticle diffusion
resistance on breakthrough curves were evaluated. The adsorption kinetics
was adjusted to the homogeneous diffusion model. The breakthrough
times of the BTEX compounds increased with an increase in the bed
height of the adsorbent and decreased with an increase in the flow.
The mathematical model and numerical methodology that were applied
represented the data of the present adsorption process with good accuracy.
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