SUBSTITUTION OF Mg2+ IN SEPIOLITE WITH Cu2+ IN AQUEOUS SOLUTIONS OF VARIOUS CUPRIC SALTS

Substitution of Mg 2+ with Cu 2+ in a fibrous clay mineral sepiolite having intracrystalline tunnels has been studied in aqueous solutions of CuS04 and Cu(CH 3 COO) 2 . Anisotropic spectra of ESR showed that the Mg2 + ions on the tunnel wall in sepiolite crystal lattice were substituted with Cu 2+ ions. The initial Cu 2+ -substitution rate in aqueous solution of CUSO 4 increased with an increase of the concentration of Cu 2+ ions. On the other hand, the initial substitution rate in aqueous solutions of Cu(CH 3 COO) 2 was independent of the concentration of Cu 2+ ions. The Cu 2+ -substitution rate in CuS04 solution was faster than that in Cu(CH3COO)2 solution. Apparent activation energies for the Mg 2+ ion-substitution of sepiolite with Cu 2+ were determined to be 21.2kJ/mol and 19.4kJ/mol in the CuSO 4 and Cu(CH 3 COO) 2 solutions, respectively.