A New Inorganic Titanium Compound with High Selective Adsorbability for Li⁺

Abstract

A new inorganic titanium compound with high selective adsorbability for Li⁺ was prepared by acid-treatment of precursory Li₂TiO₃-rich products synthesized by heating an equimolar mixture of powdered Li₂CO₃ and TiO₂ (anatase) in air at 450°-950°C. These products were examined by X-ray diffraction, chemical analysis, specific surface area (BET method), shape (TEM) and thermal (TG & DTA) analysis. For the examination of adsorbability for Li⁺ on the products, adsorption of Li⁺, Na⁺, K⁺ and Ca²⁺ for the acid-treated products was determined by a batch method in weakly basic media. The results are summarized as follows:
(1) Crystalline Li₂TiO₃ transformed to a new crystalline phase (TOH), which was characterized by the XRD peaks at d=4.74, 4.53 and 2.45Å, on acid-treatment. But the conversion decreased with increasing preparation temperature of the precursory products.
(2) Li⁺ was adsorbed selectively only on acid-treated products containing the TOH phase, suggesting that the TOH material contributed significantly to the selective adsorption of Li⁺.
(3) As the TOH phase contains TiO₂ and H₂O in the 1:1 molar ratio, it is considered that lithium-free titanium oxide hydride, H₂TiO₃, was formed from Li₂TiO₃ by the acid-treatment.
(4) When the TOH adsorbs Li⁺, a topotactic phase transformation to Li₂TiO₃ was observed. In the same manner as γ-MnO₂, the following mechanism of cation exchange is supposed for the selective Li⁺-adsorption on the TOH phase: TOH(H₂TiO₃)+2Li⁺→←Li₂TiO₃+2H⁺.
(5) The amount of adsorption of Li⁺ on TOH was influenced by the texture. The specific surface area (SSA) of the acid-treated products depended remarkably on the preparation conditions of the precursory products. The ratios of the amount of adsorbed Li⁺ to the exchange capacity increased with increasing SSA.