The formation of different Mg-AL LDHs (Mg/Al = 2:1) under hydrothermal conditions and their application for Zn2+ ions removal

Abstract

The formation of different Mg-Al LDHs (Mg/Al = 2:1) under hydrothermal conditions (200 °C; 4-24 h) was investigated in the 4MgCO3Mg(OH)2-5H2O - y-Al2O3/Al(OH)3 - H2O and Mg5(CO3)4(OH)2·4H2O - y-Al2O3 - H2O systems. It was determined that chemical nature of the initial Mg containing components changes the formation mechanism of the synthesis products during isothermal curing. Magnesium aluminum hydroxide hydrate is crystallized by using 4MgCO3Mg(OH)2-5H2O as starting material while hydroxide hydrate in the Mg5(CO3)4(OH)2·4H2O presence. The sequence of the compounds formation is presented. It should be noted that different modifications of Al containing components have only a slight influence on the meixnerite-type LDH hydrothermal synthesis. It was determined that after 45 min of sorption all Zn2+ ions are incorporated into the crystal structure of hydrotalcite. It should be underlined that crystallinity of the latter compound do not change during ion exchange experiments. Thus, the latter compound can be used as adsorbent for Zn2+ ion removal. Synthesized samples were characterized by powder X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermal analysis (STA) and scanning electron microscopy (SEM).