Molybdate sorption by Zn-Al sulphate layered double hydroxides

The efficacy of Zn–Al sulphate layered double hydroxides (LDHs) in removing molybdenum from aqueous solution was tested through sorption of aqueous molybdate by synthetic samples in batch experiments. Up to ~54% Mo is removed; the most efficient mechanism is sulphate–molybdate exchange within the LDH interlayer, which preserves the layered structure, though with a partial loss of structural order. The Mo uptake is influenced primarily by the [Zn2+]/[Al3+] ratio, which determines the ionic charge of the brucitelike layer; high ratios facilitate the release of sulphate from the interlayer and the entrance of molybdate, whilst for low ratios surface adsorption of molybdate becomes an important uptake mechanism. The Mo removing potential shown by Zn–Al sulphate LDHs may prove useful for the treatment of moderately contaminated waters.