Quintinite

Abstract: The potential for removing anionic pollutants such as F−, HAsO42−, and NO3− from water by mixed oxides issued from the moderate thermal treatment of quintinite (Mg4Al2 LDH) has been studied. This compound shows good trapping properties for F− and HAsO42−, and a low potential for NO3−, due to the competition with OH−. The competition between these three anions and CO32− has been envisaged and shows that CO32− is able to easily replace F− and NO3−, making the mixed oxides issued from MgAl LDH an inappropriate trap for F− and NO3−. However, only small amounts of arsenic are released after the CO32− introduction in water. Moreover, arsenates are able to replace carbonates even at lower concentrations. This means that HAsO42− anions present a stronger affinity than CO32− for the LDH structure. This makes mixed oxides issued from MgAl LDH very promising materials for the removal of arsenic in polluted waters.

Abstract: Comparison of layered double hydroxides (LDHs) synthesised using different methods, conditions and post-treatment is difficult to achieve because these greatly modify their material properties. This paper aims to provide a comparison of material properties for modified quintinite, where all LDHs were synthesised at the same conditions – thus allowing for direct comparison of the material properties obtained. Nano-structured materials were formed in all cases. The nano-structured transition metal (TM) MgMAl–LDHs were synthesised using constant pH co-precipitation. Five TMs (M = Fe, Co, Ni, Cu, Zn) were included in the LDH layers with molar substitutions of 0.5%, 1%, 5%, 10%, and 25% based on Mg-replacement for divalent TM cations and Al-replacement for trivalent TM cations. The materials were characterised using powder X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared analysis (ATR-FTIR), thermogravimetric analysis (TGA) and particle size analysis (PSA). The modified LDHs were synthesised free of major by-products and with similar morphologies. It could be shown that the crystallite dimensions varied between the different TM substitutions, that morphological changes were visible for some of the TMs used, that the processability depended on the TMs substituted, and that the substitution of TMs influenced the thermal stability of the LDHs.