Tratamento do pó de capim elefante por explosão a vapor e impregnação de tensoativo para adsorção de cromo em meio aquoso: processos batelada e dinâmico
Activities such as mining and tanning are the most polluting sources of heavy metals, generating toxic residues for the environment and human beings. Tanning is responsible for releasing trivalent chromium into the environment, which causes effects on the skin and, in high doses, can cause cancer...
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| Formato: | doctoralThesis |
| Idioma: | pt_BR |
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Universidade Federal do Rio Grande do Norte
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| Endereço do item: | https://repositorio.ufrn.br/handle/123456789/53524 |
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| Resumo: | Activities such as mining and tanning are the most polluting sources of heavy
metals, generating toxic residues for the environment and human beings. Tanning is
responsible for releasing trivalent chromium into the environment, which causes effects on the
skin and, in high doses, can cause cancer. In this study, the adsorption capacity of trivalent
chromium was evaluated using elephant grass (Pennisetum purpureum) as a bioadsorbent,
treated by the explosion technique and impregnated with surfactants. The samples were
characterized through compositional analysis, SEM, DRX, FRX and FTIR. The effects of
initial metal concentration (20 – 50 mg L-1), pH (2 – 6), mass of adsorbent (0.25 – 1.0g),
contact time (10 – 480 min) and temperature ( 10 – 40o C) were studied, in batch mode, with
a speed of 100 rpm. To treat the batch results, thermodynamic studies of adsorption and
kinetic isotherms were carried out under optimal operating conditions. The results appreciated
that the maximum adsorption capacity was higher (28.36 mg g-1) for elephant grass modified
simultaneously by steam explosion and surfactant impregnation (CEET). The thermodynamic
study showed that the adsorption process is not spontaneous and that the adsorption is
exothermic and chemical in nature, as well as high rates of adsorption by chromium ions. The
Langmuir model fitted better to the experimental points for all adsorbents, except for the CE
adsorbent, which fitted better to the Freundlich model. In kinetic terms, the adsorption of Cr
(III) followed a Pseudo Second Order model. A dynamic study in a fixed bed was performed
with the CEET adsorbent using a metallic solution feed rate of 300 mL min-1 and an
adsorbent mass of 6 g. The rupture curve, the adsorption capacity of the adsorbent by the
metal (85.35 mg g-1) and the estimation of the parameters: effective diffusivity (Def), axial
diffusion (DL) and external transfer efficiency (ks) were reached from the mass balance
performed in the liquid and solid phases. The model elaborated from the balance sheets
satisfactorily adjusted to the experimental points. The obtained results can be affirmed that the
techniques of treatment and modified of the bioadsorbent improved its capacity of adsorption
by the metal chromium (III). |
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