Triphosphate removal processes over ternary CaMgAl-layered double hydroxides

摘要

Mg_2-xCa_xAl-Cl-layered double hydroxides (LDHs, x = 0.0-2.0) were investigated as absorbents to remove tri-plepolyphosphate (triphosphate, TPP). The removal amount of TPP over Mg_2Al-LDH was 35.3 mg(P)/g, due to the surface adsorption and intercalation while that over Ca_2Al-LDH was 107.8 mg(P)/g LDH, attributed to the precipitation of dissolved Ca with TPP. The investigation of TPP removal over ternary Mg_(2-x)Ca_xAl-LDH (x = 0.5-1.5) demonstrated that TPP was removed predominantly either via the surface adsorption/intercalation (x = 0.5-1.0) or Ca-TPP precipitation (x =1.5). This observation reveals that there is no synergic effect between these removal processes. The detail analyses of the aqueous solution and the solid materials suggest that the release of Al in the form of Al(OH)_4 is responsible for the absence of synergy.