Layered double hydroxide stability. 1. Relative stabilities of layered double hydroxides and their simple counterparts

Solutions containing di- and trivalent metal chlorides [M(II) = Mg2+, Zn2+, Co2+, Ni2+, Mn2+; M(III) = Al3+, Fe3+] were titrated with NaOH to yield hydrotalcite-like layered double hydroxides (LDH), [[M(II)](1-x)[M(III)(x)(OH)(2)][Cl](x). yH(2)O, by way of M(III) hydroxide/hydrous oxide intermediates, Analysis of the resultant titration curves yields nominal solubility constants for the LDH. The corresponding LDH stabilities are in the order Mg < Mn < Co approximate to Ni < Zn for NI(II) and Al < Fe for M(III). The stability of LDH relative to the separate metal hydroxides/hydrous oxides is discussed.