STUDY ON THE THERMODYNAMIC EQUILIBRIUM OF Ni(II)-NH3-C2O4 2--H2O SYSTEM AND ITS APPLICATION TO THE PRECIPITATION OF ULTRAFINE NICKEL OXALATE PARTICLES

摘要

Based on the principles of simultaneous equilibrium and mass balance, a series of thermodynamic equilibrium equations of the complex system of Ni(II)-NH3-C2O4 2--H2O at ambient temperature were deduced theoretically and the relationship of lg [Ni2+] versus pH at different solution compositions was established quantitatively. From the thermodynamic diagrams, it indicated that when pH less than 8.0, free Ni2+ was the dominant metal ion in the solution; while pH larger than 8.0, most of the nickel ions coordinated with the ammonia as the complex in the solution. The experimental results show that when pH in solution less than 8.0, the nickel oxalate particles in cubic morphology were precipitated; while pH larger than 8.0, the needle-like nickel oxalate containing ammonia was obtained. Comparing the thermodynamic diagram with the experimental data, it was founded that the different existing forms of nickel ion in the solution led to the formation of the above-obtained two kinds of particles.