Na-4-mica: Cd²⁺, Ni²⁺, Co²⁺, Mn²⁺ and Zn²⁺ ion exchange

Selective cation exchange for divalent transition metals of Cd, Ni, Co, Mn and Zn has been investigated with the high-charge-density sodium fluorophlogopite mica, Na-4-mica. The Na-4-mica was easily and economically prepared by the crystallization from a mixture of NaF, MgO and metakaolin, the latter serves as an inexpensive aluminosilicate source. Ion exchange isotherms for Cd₂₊, Ni²⁺, Co²⁺, Mn²⁺ and Zn²⁺ were obtained at room temperature and the thermodynamic functions of the ion exchange equilibria were calculated. The 2Na⁺ → M²⁺ exchange with the Na-4-mica showed the following selectivity: Zn²⁺ > Ni²⁺ ≃Co²⁺ ≃Cd²⁺ > Mn²⁺. The interlayer structure of the hydrated Na-4-mica with the open interlayer space in the range 12.1-13.9 Å was retained during the ion-exchange reaction, indicating the possibility of the reversible 2Na⁺ ⇆M²⁺ exchange. The basic selective cation exchange studies of the high-charge-density ion exchanger are of relevance in recovery of metals from waste solution, and waste water treatment and disposal.