Zirconium pyrophosphate (ZrP₂O₇) is an inorganic compound with high selective adsorption capacity for cations such as caesium (Cs⁺); the mechanism is ion exchange between Cs⁺ and H⁺ on surface hydroxyl groups. Adsorption is chemical rather than physical, so it is little affected by solution acidity and remains stable over a wide pH range. An amorphous porous material with a specific surface area of about 180.7 m²/g, it has good thermal stability and is poorly soluble in water, and is mainly used to separate caesium from high-level radioactive liquid waste (recommended in acidic media at pH 1–3) and to prepare flame retardants.
