The process used for reducing the amount of impurities to a requisite minimum is known as purification of colloidal solution and it is carried out by following methods
(I) Dialysis: –
It is a process of removing a dissolved substance from a colloidal solution by means of diffusion through a suitable membrane. Since, particles (ions or smaller molecular) in a true solution can pass through an animal membrane (bladder) or parchment paper or colloidal particles. The molecules and ions diffuse through membrane into the outer water and pure colloidal solution to left behind.
(II) Electro dialysis: –
The process of dialysis is quite slow it can be made faster by applying an electric field electrodes are fitted in the compartment. The ions present in the colloidal solution migrate out to the oppositely charge to electrodes.
(III) Ultra filtration: –
In this method special filters are used, which are permeable to all substances except the colloidal particles. An ultra filter paper may be prepared by soaking the filter paper in a colloidal solution, hardening by formal dehydrate and then finally drying it. Thus, by using ultra filter paper the colloidal particles are separated from rest of the materials. The colloidal particles left on the ultra filter paper are there stirred with fresh dispersion medium (solvent) to get a pure colloidal solution.