Thermodynamics on Ammonia Leaching of Refractory Zinc Oxide Minerals

The ammonia leaching process of zinc oxide is thermodynamically analyzed based on the feature of refractory zinc oxide minerals. The reactions occurring in ammonia leaching of zinc oxide are ammonia hydration, zinc ion complex with hydroxyls, and zinc ion complex with ammonia. While there is no ammonia in the solution, the reaction of zinc ion complex with hydroxyls can be neglected. The solubility of zinc oxide is varied with the changes of the ammonia concentration and the pH, however, the total zinc concentration in solution is maintained about 1mol/L as long as the ammonia concentration is higher than 4mol/L. The leaching recovery of zinc is up to 81.89% for refractory zinc oxide minerals from Lanping Deposit by ammonia leaching with 4mol/L of ammonia solution for 38min.