Exploring the Influence of Milling Parameters on the Wet Mechanochemical Synthesis of Mg-Al Layered Double Hydroxides

Abstract

The synthesis of Mg-Al layered double hydroxide (LDH) was explored, through a one-step wet mechanochemical route, with the use of a NETZSCH LME 1 horizontal bead mill. Raw materials selected comprised of a mixture of metallic oxides/hydroxides promoting green synthesis. The research aims to expand on the understanding of the wet mechanochemical synthesis of Mg-Al LDH through variation in milling and synthesis parameters. The selected parameters investigated were rotational speed, retention time, solids loading, bead size and jacket water inlet temperature. Samples were collected, filtered and dried at 60 °C for 12 h. Unless stated otherwise, or under investigation, parameters were kept constant at pre-selected conditions adapted from existing literature. LDH synthesis was deemed to occur successfully at elevated jacket water temperatures of 50 °C and longer retention times. It was noted that Al(OH)3 XRD peak reduction occurred readily for increased rotational speeds and residence times, regardless of system temperature. MgO was deemed to react more readily at elevated temperatures. It was proposed that the amorphitisation and mechanochemical activation of Al(OH)3 contributed to its dissolution providing the relevant Al3+ ions necessary for Mg2+ isomorphic substitution. Increasing the system temperature promoted the hydration of MgO, with the absence of Mg(OH)2 attributed to its contribution as an intermediate phase prior to LDH formation.