Growth Kinetics of Manganese Sulphate from Heating and Salting‐out Batch Crystallisation

Abstract

AbstractManganese sulphate crystals can be produced in laboratory‐scale batch crystallisers by either heating or by salting‐out crystallisation. However, manganese sulphate produced through heating forms monohydrate while salting‐out mode will form the tetrahydrate. The effects of various operating conditions including supersaturation, temperature and seed dosage on growth rate of these hydrates were studied. The crystal size distribution of manganese sulphate crystals was determined by Malvern Mastersizer laser diffraction and by using a Nikon microscope with digital camera attached. The growth rate was determined from the time shft of the crystal size distribution expressed in population density numbers and by the moments method. The measurements of the growth of the crystals from ex situ microscopy supported the calculated growth rate. Salting‐out crystallisation resulted in relatively large cubic crystals, and their size and size distribution can be improved by careful control of the operating conditions. However, heating crystallisation produced irregular crystals where controlling the operating conditions has little effect on the final crystal size and size distribution with almost no observable growth.