Abstract
In this work the adsorption capacities of methylene blue on Mg-smectite and sepiolite and its derived material obtained after acid treatment and/or the addition of Fe at its surfaces are studied. Natural smectite with high Mg-content in its octahedral sheet (Mg-smectite) displays higher adsorption capacity than the sepiolite due to the ability of Mg-smectite to expand the basal spacing to accommodate methylene blue cations between adjacent layers and the inability of sepiolite to adsorb these cations within the structural channels. The acid-activation of Mg-smectite causes a clear decrease in the adsorption capacity attributed to the partial loss of the interlayer positions by the loss of the octahedral sheet and subsequent formation of amorphous silica. Moreover, the adsorption of the Mg-smectite decreases even more when iron oxohydroxides species are incorporated in its interlayer spacing making inaccessible the interlayer active sites for the adsorption of methylene blue cations. On the contrary, the microwave-assisted acid treatment of sepiolite causes a slight increase in the adsorption capacity related with the dispersion of fibers. Nevertheless, contrary to that observed with Mg-smectite, higher increasing of adsorption capacities are obtained after the formation of new adsorption centers due to the incorporation of iron oxohydroxides species at the external surfaces of sepiolite.
Highlights
IntroductionIndustrial dyes have been considered an important issue worldwide [1]
Water is an indispensable resource for the existence of life in the planet
The present study evaluates the adsorption capacity of two clay minerals with different morphologies
Summary
Industrial dyes have been considered an important issue worldwide [1]. 10–15% of these dyes are discharged into the water without pretreatment causing damage to the environment and to the human health even at low concentrations [2,3]. Several processes have been proposed to bring down the dumping of dyes into the water such as aerobic or anaerobic digestion, oxidation, ozonation, membrane separation, reverse osmosis, sedimentation, precipitation, or flotation. These treatments show a high efficiency for low scale or low proportion of dye; most of them are not competitive for larger proportions of dyes [4,5]
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