Impact of process parameters on product size and morphology in hydrometallurgical antisolvent crystallization

Abstract

The recovery of scandium from waste streams of mining and metallurgical operations presents an opportunity to balance supply and demand of this commodity. This study expands on the research focusing on the recovery of scandium as (NH4)3ScF6 from strip liquors by antisolvent crystallization using ethanol as the antisolvent. The effect of process conditions including reducing the rate of supersaturation generation, agitation mechanism, feeding point location with respect to local supersaturation, and seeding are assessed with emphasis on the final crystal size distributions (CSD) and morphology. Reducing the rate of supersaturation generation by reducing the ethanol concentration and by controlling the rate of antisolvent addition had the greatest effect on increasing the crystal sizes, although broader CSDs were obtained. Morphological modifications, without polymorphic transformations, were also observed when one-pot addition of 60 or 70% v/v ethanol was conducted, but not observed when the dilute antisolvents were fed at a controlled low addition rate.