|Class 12 Chemistry Surface Chemistry||Ultrafiltration|
This is the process of separating colloidal particles from the soluble solutes(impurities) using specially prepared filters, which are permeable to all substances except the colloid.
Colloidal particles can usually pass through filter papers as the pores are too large. An ultrafilter paper can be made by soaking the filter paper in a colloidal solution, hardening by formaldehyde and then finally drying it. As this is slow process, pressure or suction is applied to speed it up. The colloidal particles left on the ultra-filter paper are stirred with fresh dispersion medium(solvent) to form a pure colloid.