Uptake properties of phosphate on a novel Zr–modified MgFe–LDH(CO 3)

Zr–modified MgFe–layered double hydroxide is a composite of MgFe–LDH(CO 3)/Zr hydroxide. The presence of Zr hydroxide particles on the surface of LDH sheets exhibits high selectivity for phosphate in seawater. We prepared a novel Zr–modified MgFe–LDH(CO 3) composite by adding a mixed solution of MgCl 2, FeCl 3, and ZrOCl 2 and another mixed solution of 1 mol/dm 3 NaOH and 1 mol/dm 3 Na 2CO 3 to distilled water at a constant pH of 10. The composite exhibited only a poorly crystalline structure, resembling that of layered double hydroxides (LDH) from X-ray diffraction. The phosphate uptake is dependent on pH, decreasing with an increase in pH. This composite shows a much greater uptake of phosphate ions in P-enriched seawater (0.33 mg-P/dm 3) than amorphous zirconium oxide and MgFe–LDH(CO 3). The uptake isotherm was fitted with a Freundlich relation. These phosphate-uptake behaviors closely resemble those of the relevant Zr–MgAl–LDH, which is estimated to be a composite of MgAl–LDH with amorphous zirconium hydroxide on the surface from X-ray absorption spectroscopy. Therefore, a similar structure of Zr–modified MgFe–LDH(CO 3) composite probably causes the marked increase in phosphate uptake from P-enriched seawater.