Crystalline insoluble acid salts of tetravalent metals—XXI ion exchange mechanism of alkaline earth metal

One-Pot Synthesis of Layered Disodium Zirconium Phosphate: Crystal Structure and Application in the Remediation of Heavy-Metal-Contaminated Wastewater

Inorganic ion exchangers offer advantages whenever operation at high temperatures or in oxidizing environments is required. A novel two-dimensional disodium zirconium phosphate, Zr(NaPO₄)₂·H₂O, was reported and investigated as an ion exchanger for heavy metals. The material was synthesized by a novel minimalistic solventless approach, and its solid-state structure was determined from powder X-ray diffraction data. Zr(NaPO₄)₂·H₂O crystallizes in the space group P2₁/c with cell parameters a = 8.7584(1) Å, b = 5.3543(1) Å, c = 18.1684(3) Å, β = 109.053 (1)°, and Z = 4. Its layered structure is similar to that of α-zirconium phosphate, Zr(HPO₄)₂·H₂O. However, unlike α-zirconium phosphate which is limited in practical applications by its narrow interlayer spacing (d = 7.6 Å), the disodium zirconium phosphate has a larger spacing of 8.6 Å between planes. The material with inherent structural advantages displays excellent sorption for heavy metals such as Pb²⁺, Cu²⁺, Cd²⁺, and Tl⁺, maintaining its high selectivity with distribution coefficients, K_d, of 10⁴-10⁵ mL/g even in the presence of a large excess of Na⁺, K⁺, Mg²⁺, and Ca²⁺, which are commonly present in underground water. In particular, the maximum sorption capacity for the highly toxic Tl⁺ is a record high, 5.07 mmol/g (1036 mg/g). The fast reaction kinetics indicate that the exchangeable positions in Zr(NaPO₄)₂·H₂O are readily accessible, in contrast to Zr(HPO₄)₂·H₂O. The ease of preparation, benign nature, and advantageous ion-exchange properties make Zr(NaPO₄)₂·H₂O a highly promising sorbent for the treatment of water polluted with heavy metals.

Layered double hydroxide and zirconium phosphate as ion exchangers for the removal of ‘black crusts’ from the surface of ancient monuments

Two ion exchanger solids (LDH and ZrP) as an innovative tool to remove gypsum from ancient monuments.