Ion-exchange and Structural Properties of Magadiite

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The ion-exchange reactions of Na-magadiite with metal cations such as H⁺, K⁺, Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺ and Zn²⁺ were studied in an aqueous medium. The H+ ion and all divalent metal ions except Mg²⁺ exchanged with Na⁺ in an aqueous solution with a stoichiometric amount of the metal ion. K⁺ and Mg²⁺ showed poor reactivity with the Na-magadiite. Na⁺ was not fully replaced even with a K⁺ or Mg²⁺ concentration that was 100 times the Na⁺ concentration. The pH dependence of Cu²⁺ for the ion-exchange reaction was different from that of other metal ions. XRD analysis revealed that the structure of the Na-magadiite differed from the Cu-or H-magadiite. These differences arose from structural changes in the silicate sheet due to the H⁺ or Cu²⁺ adopting a different geometry in interaction with the oxygen atoms in the silicate sheet. Ethylene diamine (en) and pentaethylene hexamine (pentaen) react with Cu²⁺ to form stable cationic complexes: Cu (en) ₂, which has a planar structure, and Cu (pentaen), which has an octahedral structure. The XRD patterns all revealed a difference between the basal spacings of the metal-magadiite and the sum of the crystalline ionic diameter of the metal and basal spacing of the H-magadiite. Na⁺ remained in the interlayer of the magadiite in the presence of excess complexes. The degree of dehydration of the metal cation depends on the ion-exchange reactivity of the magadiite.