REDUCTION-DISSOLUTION OF COBALT OXIDE IN ACID-MEDIA - A KINETIC-STUDY

The kinetics of cobalto-cobaltic oxide (Co3O4) dissolution in sulphuri c acid have been investigated. The dissolution rate is significantly e nhanced by the use of Na2SO3 in aqueous media for the reduction of Co3 + to Co2+. The dissolution was studied as a function of rate of agitat ion, leaching time, acid concentration, temperature and Na2SO3 concent ration. The reaction has a 1/2 order of dependence on acid concentrati on between 1.0 and 4.0 M. The rate of dissolution appears to be indepe ndent of the SO32- concentration above 0.025 M. Primary identification of the rate-controlling step has been accomplished by close fitting e xperimental data to the predicted reduced time plots for diffusion of the reactant species across the unreacted solid layer. The activation energy for the temperature range 303-343 K was found to be 25 kJ/mol, thereby confirming diffusion as the rate-controlling step.