A green route to synthesize layered double hydroxides

This article demonstrates a green route for synthesis of Ca‐doped [Mg 3 Al(OH) 8 ]Cl from a reaction of AlCl 3 ·6H 2 O, Mg(OH) 2 , Ca(OH) 2 , and NH 3 ·H 2 O in water, which produces only the desired solid product and a by‐product NH 4 Cl in the mother solution; therefore, they can be separated easily by filtration or centrifugation. Being carefully designed, enough NH 4 Cl can be crystallized from the mother solution, which could be used as a fertilizer; while the distilled water be used to wash the products for the last time; the mother solution that still contains some NH 4 Cl and filtrate from the first time washing of the product can be used to prepare the LDH again. By using cheaper Mg(OH) 2 and Ca(OH) 2 instead of MgCl 2 ·6H 2 O and CaCl 2 ·2H 2 O, the process is more economic and produces less NH 4 Cl. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 234–239, 2015