Fines Formation (and Prevention) in Seeded Precipitation Processes

Abstract

An overview of three studies on seeded precipitation in a fluidised bed reactor (FBR) is presented. The objective of using the FBR is to remove dissolved metals as precipitated metal salts onto a seed surface. For the nickel hydroxy-carbonate system (S =±10⁵), particle enlargement was found to occur by a combination of growth and aggregation. The concentration of fines correlated with the degree of supersaturation in the reactor, which suggests that fines formation was due to homogenous nucleation, attrition of rough growth precipitate, or a combination of the two. Reducing the local supersaturation by multiplying the feed points was found to be a successful fines control strategy.
For the mixed nickel/cobalt sulphide system, (S =±10¹¹ for nickel and ± 10¹² for cobalt), a significant quantity of fines was formed but these eventually aggregated onto the seeds. In contrast, for the copper sulphide system(S =±10³⁴), the fines formed immediately but never aggregated onto the seed material and it was not possible to control the supersaturation levels to the extent that fines formation was avoided.