Development of magnesium–iron layered double hydroxide and application to nitrate removal

Nitrate is an important ion in agriculture and industry although it is known to cause eutrophication and affect human health. Removal of nitrogen by physicochemical treatment such as sedimentation and membrane separation remains difficult. The selectivity of commercial adsorbents for nitrate is among the lowest for anions, because the selectivity of an adsorbent as an ion exchange resin is based on the valence of the ion. Layered double hydroxide acts as an anion adsorbent, and the target anion adsorbs in the interlayer of cations. In this study, we focused on nitrate adsorption by magnesium-iron layered double hydroxide. The results indicate that the magnesium to iron ratio controlled the interlayer distance. The interlayer distance increased as the magnesium to iron ratio increased. The maximum adsorption capacity for nitrate of 1.80 mmol/g suggests the optimum magnesium to iron ratio is 3. The interlayer distance for a magnesium to iron ratio of 3 is similar in size to that of nitrate. The phosphate inhibition of nitrate adsorption suggests the formation of phosphate compounds on the adsorbent’s surface.