Effective removal of pyrophosphate by Ca-Fe-LDH and its mechanism

Pyrophosphate (PP), as a dispersant in industrial activities, has attracted much attention due to its contribution to the eutrophication in aquatic ecosystem. This study investigated the efficient PP removal over Ca-based layered double hydroxide (LDH). The PP removal amount was 4.54 mmol P/g LDH at initial total phosphate concentration [P] ranging from 1.61 to 6.45 mmol/L in which LDH dissolved and Ca2P2O7 center dot 2H(2)O precipitated. Moreover, LDH hydrolysis led to Ca-containing Fe hydroxide (Ca0.66FeO1.51(OH)(1.30)center dot 0.35H(2)O) formation. The major PP removal route was precipitation as Ca2P2O7 center dot 2H(2)O while Ca-containing Fe hydroxide removed PP through surface capture only in a small portion. We concluded that the combination of surface capture and precipitation process enhanced PP removal over Ca-Fe-LDH and made it as a potential material to remove PP efficiently. (C) 2011 Elsevier B.V. All rights reserved.