A process utilizing ozone for the oxidation/precipitation of nickel from sulfate solutions as a recovery option from dilute streams has been studied using a semi-batch bubble column reactor. The results demonstrated that a minimum pH (approximate to 6.8) was required for the reaction to proceed, evidently because the first step is the formation of nickel (II) hydroxide, which is then oxidized to produce beta-NiOOH (nickel oxy hydroxide). The sequence of reactions is proposed. Ozone consumption exceeds stoichiometric, possibly due to side reactions with base added to maintain pH. Some physical characteristics of NiOOH, particle size distribution, morphology, density, and settleability, were determined and compared with Ni(OH)(2). (c) 2004 Elsevier Ltd. All rights reserved.