Filterability and ageing of crystalline potassium sulphate salted-out with ethanol and acetone

The desupersaturation and ageing of a solid/liquid suspension consisting of crystalline and dissolved potassium sulphate, co-solvent water and an anti-solvent, i.e. acetone or ethanol, were investigated based on image analysis, measurements of electronic conductivity and determination of certain filterability parameters. The crystals were produced by salting-out precipitation at 25°C. The samples were taken after addition of the anti-solvent in a semi-batch process by pumping the precipitant at constant flow rate or in a batch process by adding all the anti-solvent at the beginning of the precipitation process. The studied ageing time was 60 mins. Ostwald ripening theory was utilized to compare the ripening tendency in the studied solvent systems. The precipitation conditions were changed by altering the flow rate of the precipitant. The solution composition was changed by adding sulphuric acid to decrease the pH from a neutral solution pH equal to 6.2. Ageing for 60 mins. decreased the cake resistances of both studied precipitant systems whereas cake porosities varied only slightly between fresh and aged precipitate cakes.