Abstract
Substitution of Mg2+ with Cu2+ in a fibrous clay mineral sepiolite having intracrystalline tunnels has been studied in aqueous solutions of CuSO4 and Cu (CH3COO) 2. Anisotropic spectra of ESR showed that the Mg2+ ions on the tunnel wall in sepiolite crystal lattice were substituted with Cu2+ ions. The initial Cu2+-substitution rate in aqueous solution of CuSO4 increased with an increase of the concentration of Cu2+ ions. On the other hand, the initial substitution rate in aqueous solutions of Cu (CH3COO) 2 was independent of the concentration of Cu2+ ions. The Cu22+-substitution rate in CuSO4 solution was faster than that in Cu (CH3COO) 2 solution. Apparent activation energies for the Mg2+ ion-substitution of sepiolite with Cu2+ were determined to be 21.2 kJ/mol and 19.4 kJ/mol in the CuSO4 and Cu (CH3COO) 2 solutions, respectively.
