The kinetics of the exchange of cobalt(II) ions between NaCl and Na₂O-SiO₂-Fe₂O₃ melts in the temperature range 1200 to 1400 K

Abstract

Studies of the equilibria and kinetics of the Co²⁺ ion exchange in the Na₂O-SiO₂-Fe₂O₃/NaCl system were performed over the 1200 to 1400 K temperature range by measuring the emf of galvanic cells of the following composition:

$$( - )Co\left| {\frac{{NaCl - CoCl_2 }}{{Na_2 O - SiO_2 - Fe_2 O3}}} \right.\left| {NaCl - CoCl_2 } \right.\left| {Co( + )} \right.$$

Distribution coefficients α of the Co²⁺ ions between the salt phase and silicate melt are of the l0⁻² order. Differential equations describing the transfer process of the Co²⁺ ions from the salt phase to the silicate phase were solved. The diffusion coefficients D_Co ²⁺ in the Na₂O-SiO₂-Fe₂O₃ melt were determined by substituting the Co²⁺ ion concentration change in fused NaCI into the differential equations. The values of D_Co ²⁺ are about 10⁻⁵ cm²S⁻¹ and they decrease with decreasing temperature and increasing Fe₋₂O₋₃ content in slags. The diffusion coefficient of the cobalt (II) ions in slags determined in this way is consistent with that determined by the otating disk method.