• Sulfite activation results in less magnetic resultant iron particles • Activation further influences particle morphology and size distribution • Sulfite activation may impede downstream physiochemical water treatment processes ABSTRACT The activation of ferrate with sulfite increases oxidative transformation of recalcitrant organic compounds; however, it also changes the characteristics of the iron particulates that result from the ferrate reduction. In this study, particles resulting from ferrate reduction both with and without sulfite were compared in a laboratory matrix simulating water treatment conditions at the bench-scale. Characteristics examined included magnetization, morphology, size, and surface charge. The activation of ferrate with sulfite changed the characteristics of resultant particles in several important ways. Activated ferrate resultant particles were less magnetic, more polydisperse including a higher fraction of nanoparticles, and exhibited a less-crystalline morphology compared to particles resulting from ferrate self-decay. Surface charges between the two particle types were similar, and negative. The relatively rapid formation of Fe(III) from Fe(VI) activation leads to particles of different character, likely though a greater supply of precursory low molecular weight iron hydroxo-species. Particles resulting from activated ferrate used as a preoxidant will impact downstream processes in important