Evidence of the influence of the cationic composition on the anionic affinity of layered double hydroxides

The effect of the cationic composition on the anionic affinity is evaluated by studying the reconstruction of the layered double hydroxide structure from mixed oxides obtained by the heat treatment of the Mg₄Al₂-layered double hydroxides solid solution, in aqueous solutions containing carbonates, sulfates, and nitrates. After synthesis, all the samples present the same c parameter whatever the iron content. After a thermal treatment at moderate temperature, amorphous mixed oxides are obtained from all the samples. The influence of the cationic composition is clearly demonstrated on the anionic affinity as the Mg₄Al₂-amorphous mixed oxides reconstructs the layered double hydroxide structure with 90 % carbonates and 10 % sulfates whereas the Mg₄Fe₂-amorphous mixed oxides reconstruct the layered double hydroxide structure with 89 % carbonates, 7 % sulfates, and 4 % nitrates. The nitrate ratio increases as the iron content increases.