High adsorption selectivity of ZnAl layered double hydroxides and the calcined materials toward phosphate.

The selective adsorption of phosphate ions was investigated on CO(3)(2-), Cl(-), and NO(3)(-)-type ZnAl layered double hydroxides (LDHs) and the calcined CO(3)(2-)-type LDH at 200, 400, 600 and 800 degrees C, respectively. The calcined LDHs and NO(3)(-)-type LDH showed high selectivity toward phosphate ions, while the Cl(-)-type LDH shows selectivity toward both SO(4)(2-) and phosphate ions. The NO(3)(-)-type LDH selectively adsorbed phosphate ions mainly through ion exchange. The calcined samples possibly proceed through ligand complexation or electrostatic attraction between phosphate ions and hydrated ZnO formed after calcination, although the structural memory effect was observed for the samples calcined below 600 degrees C with the formation of CO(3)(2-)-type LDH. Adsorption/desorption behaviors indicated that the calcined samples had good stability and reusability. 2009 Elsevier Inc. All rights reserved.