**1. Introduction**

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 <sup>M</sup>2+1−<sup>x</sup>M3<sup>+</sup>x(Az−)x/z(OH)2·nH2O.

Their capacity to easily exchange the interlayer anions makes LDHs attractive as carriers or scavengers of potential toxic anions [3–6]. Furthermore, their flexible structure, which can be reproduced using several bivalent and trivalent cations, suggests the possibility to use LDHs as a getter of pollutant cations [7,8]. For all of the above, the knowledge of the relationships between metals and LDHs is fundamental to allow the use of these minerals [9].

In a previous study, the relationships between lanthanides metals and a woodwardite (CuAl–SO4 LDH) structure were investigated [10], with the aim to use these materials for the recovery of the rare earth elements from waste electric and electronic equipment for both georemediation and georecovery exploitation. The aim of this work is the synthesis and characterization of two different LDHs to experimentally investigate their capability to recover pollutants from wastewater. Such wastewater has been taken from a galvanic plant. Its composition is enriched in environmentally hazardous anions and metal cations, which derive from the treatment process. This problem is widespread [11]. Many di fferent treatments have been proposed to solve this contamination issue [12,13]. In this study, the exchange capability of the two compounds is tested directly on this real wastewater, based on the results previously obtained in a laboratory-prepared Cr2O7 2− solution [14]. The selected compounds are LDHs, as they represent a cheap and e ffective method to remove pollutants from aqueous solutions. The two compounds investigated are a NiAl-NO3 and a MgAl-CO3 LDHs. The choice of these compositions is based on the fact that previous works have shown the chromate uptake capacity by similar LDHs both intercalated with other sorbents [15] and through an ion exchange reaction with the interlayer anion [16,17].
