Triphosphate removal processes over ternary CaMgAl-layered double hydroxides

Mg2-xCaxAl-Cl-layered double hydroxides (LDHs, x = 0.0–2.0) were investigated as absorbents to remove triplepolyphosphate (triphosphate, TPP). The removal amount of TPP over Mg2Al-LDH was 35.3 mg(P)/g, due to the surface adsorption and intercalation while that over Ca2Al-LDH was 107.8 mg(P)/g LDH, attributed to the precipitation of dissolved Ca with TPP. The investigation of TPP removal over ternary Mg2-xCaxAl-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.

► We examined the removal of triphosphate (TPP) using Mg2-xCaxAlCl-LDH (x = 0–2).
► The LDHs (x = 0.0, 0.5, 1.0) removed TPP via the surface adsorption/intercalation.
► LDHs (x = 1.5, 2.0) released Ca2+ to precipitate TPP as insoluble Ca5(P3O7)2·mH2O.
► Al-based ternary LDHs enhanced TPP removal capacity by improving Ca dissolution.