Abstract
Owing to their structure, layered double hydroxides (LDHs) are nowadays considered as rising materials in different fields of application. In this work, the results obtained in the usage of two different LDHs to remove, by adsorption, some cationic and anionic pollutants from industrial wastewater are reported. The two compounds MgAl-CO3 and NiAl-NO3 have been prepared through a hydrothermal synthesis process and then characterized by means of PXRD, TGA, FESEM, and FTIR spectroscopy. The available wastewater, supplied by a galvanic treatment company, has been analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES), resulting as being polluted by Fe(III), Cu(II), and Cr(VI). The water treatment with the two LDHs showed that chromate is more efficiently removed by the NiAl LDH through an exchange with the interlayer nitrate. On the contrary, copper and iron cations are removed in higher amounts by the MgAl LDH, probably through a substitution with Mg, even if sorption on the OH− functional groups, surface complexation, and/or precipitation of small amounts of metal hydroxides on the surface of the MgAl LDH could not be completely excluded. Possible applications of the two combined LDHs are also proposed.
Highlights
Layered double hydroxides (LDHs) belong to a family of minerals, the so-called hydrotalcite supergroup, whose crystal structure consists of brucite-type layers, in which a trivalent cation partially substitutes a divalent cation [1,2]
Based on the results reported in the literature about the adsorption of anions and cations [7,11], in this work the adsorption efficiency of different pollutants was tested on a real industrial wastewater sample
It is possible to state that the synthesis of the MgAl-CO3 layered double hydroxides (LDHs) yielded a material with a crystallite size significantly higher than the NiAl-NO3 LDH
Summary
Layered double hydroxides (LDHs) belong to a family of minerals, the so-called hydrotalcite supergroup, whose crystal structure consists of brucite-type layers, in which a trivalent cation partially substitutes a divalent cation [1,2] This substitution produces a net positive charge balanced by the entrance of an anionic species in the interlayer, giving as a general formula M2+ 1−x M3+ x (Az− )x/z (OH)2 ·nH2 O. Their capacity to exchange the interlayer anions makes LDHs attractive as carriers or scavengers of potential toxic anions [3,4,5,6]. For all of the above, the knowledge of the relationships between metals and LDHs is fundamental to allow the use of these minerals [9].
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