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

. Pyrophosphate was effectively removed by Ca–Fe–LDH with the maximal uptake amount of 4.54 mmol/g. The removal mechanism included the dissolution of LDH, precipitation of Ca 2P 2O 7·2H 2O and surface capture of pyrophosphate. [Display omitted] ► Pyrophosphate removal was investigated on Ca–Fe–LDH at first time. ► The maximal uptake amount was 4.54 mmol/g. ► The LDH dissolution provided Ca-contained Fe hydroxide and soluble Ca 2+. ► Pyrophosphate was removed by precipitation combined with surface capture. 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 Ca 2P 2O 7·2H 2O precipitated. Moreover, LDH hydrolysis led to Ca-containing Fe hydroxide (Ca 0.66FeO 1.51(OH) 1.30·0.35H 2O) formation. The major PP removal route was precipitation as Ca 2P 2O 7·2H 2O 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.