title: Selective Crystallization of Phosphoester Coordination Polymer for the Separation of Neodymium and Dysprosium: A Thermodynamic Approach.
abstract: Thermodynamics of the formation of coordination polymers (CPs) or metal-organic frameworks (MOFs) has not been focused on, whereas many CPs or MOFs have been synthesized in a solution. With a view of separating Nd3+and Dy3+in an aqueous solution, we demonstrate that crystallization of the CPs of Nd3+and Dy3+based on dibutyl phosphoric acid (Hdbp) can be thermodynamically described; crystallization yields of [Ln(dbp)3] (Ln = Nd or Dy) complex are predicted well using a simple calculation, which takes the apparent solubility products (Kspa) for [Ln(dbp)3] and the acid dissociation constant of Hdbp into account. The Kspavalues of [Nd(dbp)3] and [Dy(dbp)3] are experimentally determined to be (1.3 ± 0.1) × 10-14and (2.9 ± 0.4) × 10-18M4, respectively, at 20 °C. The ratio of these Kspavalues, that is, ca. 4500, is significantly larger than the ratio of the solubility products for inorganic salts of Nd3+and Dy3+. Therefore, Nd3+and Dy3+are selectively crystallized in an aqueous solution via the formation of CPs. Under optimized conditions, Dy3+crystallization is preferable, whereas Nd3+remains in the solution phase, where the ratio of the Dy molar content to the total metal content (i.e., Nd + Dy) in the crystal is higher than 0.9. The use of acids, such as HCl or HNO3, has no practical impact on the separation in an aqueous solution.
authors.affiliation: Environmental Management Research Institute, National Institute of Advanced Science and Technology (AIST) , 16-1 Onogawa, Tsukuba 305-8569, Ibaraki, Japan.
authors.forename: Yuiko
authors.identifier: 0000-0002-4777-7541
authors.initials: Y
authors.lastname: Tasaki-Handa
authors.affiliation: Environmental Management Research Institute, National Institute of Advanced Science and Technology (AIST) , 16-1 Onogawa, Tsukuba 305-8569, Ibaraki, Japan.
authors.forename: Yukie
authors.initials: Y
authors.lastname: Abe
authors.affiliation: Environmental Management Research Institute, National Institute of Advanced Science and Technology (AIST) , 16-1 Onogawa, Tsukuba 305-8569, Ibaraki, Japan.
authors.forename: Kenta
authors.initials: K
authors.lastname: Ooi
authors.affiliation: Environmental Management Research Institute, National Institute of Advanced Science and Technology (AIST) , 16-1 Onogawa, Tsukuba 305-8569, Ibaraki, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Narita
authors.affiliation: Environmental Management Research Institute, National Institute of Advanced Science and Technology (AIST) , 16-1 Onogawa, Tsukuba 305-8569, Ibaraki, Japan.
authors.forename: Mikiya
authors.initials: M
authors.lastname: Tanaka
authors.affiliation: Environmental Management Research Institute, National Institute of Advanced Science and Technology (AIST) , 16-1 Onogawa, Tsukuba 305-8569, Ibaraki, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Wakisaka