Minerals for wastewater purification: a case study

Amongst the various strategies studied to reduce polluting agents in water, both from anthropogenic and natural sources, adsorption processes are among the most widespread techniques. Layered double hydroxides (LDH, anionic adsorbers) play a fundamental role in the treatment of industrial wastewater, which often contains both anionic and cationic species. The objectives of the present study were to synthesize a (Mg, Zn)Al-NO3 LDH, and a composite between the LDH and montmorillonite (Mnt, cationic exchanger), and to test their adsorption capacity for both cationic and anionic pollutants in two different samples of industrial wastewater. The compounds were characterized by means of inductively coupled plasma-atomic emission spectroscopy (ICP-AES), X-ray powder diffraction (XRPD), Fourier-transform infrared (FT-IR) spectroscopy, differential thermal analysis/thermogravimetry (DTA-TG), and transmission electron microscopy (TEM). Results of product yields and extraction performance provided evidence that the synthesized compounds were active in the removal of various kinds of pollutants from real wastewaters. The adsorption capacity, in the case of the removal of cations varied from similar to 85 to 100% and from similar to 92 to 100% when the LDH and the LDH-Mnt, respectively, were used. The 56-100% removal of anions was instead obtained for both the adsorbents.