Abstract
The efficiency of acid treatment on natural calcium bentonite (natural bentonite) for anionic dye adsorption was investigated using methyl orange (MO) as a probe. Additionally, adsorption experiments were accomplished between the natural bentonite, acidified bentonite, and a cationic dye (methylene blue, MB). Acid functionalization in natural bentonite (RF) was carried out with HCl and H2SO4 acids (RF1 and RF2, respectively). The samples were characterized by chemical analysis, mineralogy, particle size, and thermal behavior with the associated mass losses. The adsorption efficiency of MO and MB dyes was investigated by the effects of the initial concentration of adsorbate () and the contact time (). The acid treatment was efficient for increasing the adsorption capacity of the anionic dye, and the values measured were 2.2 mg/g, 67.4 mg/g e 47.8 mg/g to RF, RF1 e RF2, respectively. On the other hand, the acid functionalization of bentonite did not significantly modify the MB dye adsorption. The Sips equation was the best fit for the adsorption isotherms. Thus, we found that the acid-functionalized bentonite increases the anionic dye adsorption by up to 8000%. The increased adsorptive capacity of acidified bentonite was explained in terms of electrostatic attraction between the clay surface and the dye molecule.
Highlights
Synthetic dyes are polluting agents with complex, non-biodegradable chemical structures that cause harmful effects both for the aquatic life and for human beings [1]
This study aims at investigating the efficiency of the acid treatment in Brazilian calcium bentonite from the state of Paraiba for adsorption of the anionic dye methyl orange
The purpose of this paper was to evaluate the efficiency of the acid treatment in Brazilian bentonite for the adsorption of anionic dye methyl orange
Summary
Synthetic dyes are polluting agents with complex, non-biodegradable chemical structures that cause harmful effects both for the aquatic life and for human beings [1] These dyes can be classified as anionic, cationic, and non-ionic [2]. Methylene blue (cationic dye) does not have high toxicity but may cause harmful effects on human health, such as vomiting, increased heart rate, diarrhea, and cyanosis [6]. Disposing of both dyes in wastewaters in streams and aquifers may hamper reoxygenation and prevent aquatic life photosynthesis [7,8,9]
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