One-step recovery of cobalt from ammonia-ammonium carbonate system via pressurized ammonia distillation

Ammonia leaching of Co-bearing resources has attracted attention due to its selectivity to cobalt and mild leaching conditions. However, in ammonia leach liquor, cobalt and ammonia are complexed stably, which undoubtedly increases the difficulty of preparing cobalt products from the solution. In this study, ammonia distillation process was proposed and studied to recover cobalt from NH₃-(NH₄)₂CO₃ system. First, the E-pH diagram of Co-NH₃-CO₃^2--H₂O system was drawn, and the possibility of preparing cobalt products from the solution was discussed. Then, by comparing atmospheric and pressurized ammonia distillation processes, it was found that the microspherical Co₃O₄ product can be obtained directly through pressurized ammonia distillation. Furtherly, the effects of parameters on this process and the formation mechanism of Co₃O₄ were investigated systematically. Over 99% of cobalt could be recovered in one step under optimal conditions. Finally, CoCO₃ products with different morphologies were also obtained directly by adding the reducing agent during pressurized ammonia distillation, and the cobalt recovery rate was hardly affected. The evaporated ammonia and residual solution can be recycled. This work realizes the one-step preparation of cobalt products and provides a new perspective on cobalt recovery from ammoniacal solution.