Removal of humic substances by layered double hydroxide containing iron

Hydrotalcite and hydrotalcite-like compounds containing iron were synthesized. The effect of their physicochemical structure on the adsorption properties for humic substances were elucidated following the characterization of the compounds. The compounds and their heat-treated ones showed a high adsorption capacity for the humic substances dissolved in water. The following adsorption and/or removal mechanisms were suggested through the series of the studies. The removal of the humic substances occurs by both the intercalation of humic substances into the positively charged innerlayer (ion-exchange) and the adsorption onto hydroxyl groups of the compounds. The buffering pH function of the compounds enlarges the removal by producing hydroxides through their slight dissolution. The produced hydroxides coagulate the humic substances onto the compounds, resulting in a sludge with low water content. The additive salt increases the amount of adsorption. The compounds were found to be effective insoluble adsorbents for the removal of humic substances.