Preparation of basic nickel carbonate particles in solution system of Ni（ Ⅱ ）-NH3-CO3^2——H2O

Based on the principles of simultaneous equilibrium and mass balance, a series of thermodynamic equilibrium equations ot Ni( Ⅱ )-NH3-CO3^2--H2O system at ambient temperature were deduced theoretically and the thermodynamic diagrams of Ig[Ni]T versus pH at different solution compositions were drawn, which was quite effective to explain the formation mechanism of precipitation particles with different microscopic shapes. When pH of the solution is below 7.0， free nickel ions are dominant and when the precipitant is added， the fast coagulation will take place leading to the loose flocculation particles. While pH is above 7.0, because of the coordination of nickel ion with ammonia, the precipitation proceeds slowly accompanying with the release of Ni^2 from the multi-coordinated Ni(NH3)n^2 (n=1, 2,.., 6), which easily leads to the formation of the dense spherical particles.