Nickel carbonate precipitation in a fluidized-bed reactor

Carbonate precipitation of nickel in pellet reactors has several advantages over the more commonly used hydroxide sludge process. As a seeded precipit ation, no sludge is formed; instead, there is a dense precipitate permittin g easy solid-liquid separation and reuse of the nickel by dissolving the pe llets. Furthermore, carbonate precipitation occurs at a lower pH, thus redu cing the postneutralization costs of the stream. A laboratory-scale fluidiz ed bed was used in order to study the precipitation processes relevant for pellet reactor technology. Different profiles of the bed were established t o determine the relative importance of the various precipitation phenomena such as homogeneous and heterogeneous nucleation. The rapid kinetics of nic kel carbonate nucleation, driven by high local supersaturation, formed a la rge amount of fines that agglomerated slowly up the bed. In general, the ni ckel removal efficiency not only was solubility dependent but was largely i nfluenced by the fines nucleation, and thus by the supersaturation profile of the reactor.