Continuous Precipitation of Nickel Hydroxide by Addition of Ammonium Ions

Spherical and dense nickel hydroxide, Ni(OH)2, particles are produced by addition of ammonia or ammonium ions, NH4+, using a continuous precipitation. In this study, the nickel ion, Ni2+, concentrations and the NH4+ concentrations in a suspended solution for the continuous precipitation of Ni(OH)2 are examined, and the formation behaviors of spherical and dense Ni(OH)2 particles are discussed by the relations between the Ni2+ and NH4+ concentrations. When NH4+ was supplied into a suspended solution during the continuous precipitation of Ni(OH)2, Ni2+ was present in a steady state and the Ni2+ concentrations changed with the NH4+ concentrations in a feed solution, with the solution pH and the residence times of suspended solutions in a crystallizer. The ratios of the NH4+ concentrations to the Ni2+ in a solution at steady state were different from the coordination number of NH3 in a nickel ammine complex. Formation of Ni(OH)2 precipitates when adding NH4+ is discussed by the relations between the Ni2+ and the NH4+ concentrations in suspended solution for continuous and batch operations.