A two-stage reduction process for the production of high-purity ultrafine Ni particles in a micro-fluidized bed reactor

•High purity and low density ultrafine nickel powder was prepared by a two-stage reduction process.•Formation of agglomerated Ni particles at lower temperatures was crucial to avoiding defluidization.•A concept design of a two-stage fluidized bed reactor process was proposed for Ni production.•This method may be extended to synthesis of other nanoparticles.

A novel two-stage reduction process for synthesis of ultrafine nickel powder with a high purity and low density in a fluidized bed reactor has been developed in this work. The raw ultrafine NiO particles are first pre-reduced using hydrogen at lower temperatures (340–400 °C), followed by further reduction at higher temperatures (500–600 °C). The self-agglomeration of Ni particles formed during low-temperature reduction decreases the sintering activity of the newly formed ultrafine Ni particles, leading to good fluidization quality, even for the subsequent high-temperature reduction process. The agglomerated Ni particles have a high Ni content (above 99 wt%), a low density (0.78 g/cm3) and a uniform particle size (approximately 100 μm). A concept design for a novel two-stage fluidized bed reactor process used to produce high-purity Ni powder was also proposed. This approach may be extended to the synthesis of other ultrafine/nanosized metals or metal oxides through a fluidization method.

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