Carbonate precipitation of nickel in pellet reactors has several advantages over the more commonly used hydroxide sludge process. As a seeded precipitation, no sludge is formed; instead, there is a dense precipitate permitting easy solid-liquid separation and reuse of the nickel by dissolving the pellets. Furthermore, carbonate precipitation occurs at a lower pH, thus reducing the postneutralization costs of the stream. A laboratory-scale fluidized bed was used in order to study the precipitation processes relevant for pellet reactor technology. Different profiles of the bed were established to determine the relative importance of the various precipitation phenomena such as homogeneous and heterogeneous nucleation. The rapid kinetics of nickel carbonate nucleation, driven by high local supersaturation, formed a large amount of fines that agglomerated slowly up the bed. In general, the nickel removal efficiency not only was solubility dependent but was largely influenced by the fines nucleation, and thus by the supersaturation profile of the reactor.