Growth rate dispersion of ammonium sulphate attrition fragments

Abstract

In most suspension crystallisation processes secondary nucleation is the dominant nucleation mechanism. Therefore, the secondary nucleation rate and the subsequent growth of the attrition fragments must be described adequately. Attrition fragments however often feature growth rate dispersion, a phenomenon that is still not understood properly. Attrition fragments of ammonium sulphate were created in a 2-l draft tube crystalliser from parent crystals that were suspended using a marine impeller at 300 rpm. Attrition fragments at a supersaturation of σ 1 = 0.004 showed a large dispersion ranging from dissolving crystals to a growth rate of 35 nm s - 1 . The larger fragments on average grew faster than the smaller fragments. At lower super saturation ( σ 2 = 0.002 ) fragments exhibited only zero-growth and total or partial dissolution. At these conditions the smaller fragments on average dissolved faster than the larger fragments.