Preparation of spherical zirconium salt particles by homogeneous precipitation

Spherical basic zirconium sulphate particles were prepared by homogeneous precipitation in mixed solutions of zirconium sulphate and urea. Values of [SO₄^2–]/[Zr⁴⁺] and [urea]/[Zr⁴⁺] in starting mixed solutions and cooling rate may affect the formation of spherical particles. Complexes such as [Zr(OH)_n]^4–n could prevent the formation and thus lead to gel precipitation. In addition, spherical particles could only be obtained in the presence of SO₄^2–; for NO^3– and Cl^–, only gel precipitation occurred.