The colloidal solution is the solution that has the particle size ranging from true solutions and suspensions. The range of the diameter of a dispersed particle is from 10 Angstrom to 2000 Angstrom.
Methods for Purification:
Some of the methods of purification of the colloidal solution are as follows:
The process in which the ions are removed from the solution by the phenomenon of diffusion through a permeable membrane is known as dialysis. In this process, a sol consisting of ions or molecules is filled in a permeable membrane bag, dipped in the water. The ion from the solution diffuses from the permeable membrane. Because of the continuous flow of water, the concentration of electrolyte outside the membrane is neutralized. For e.g.: Ferric hydroxide sol is purified by using this method.
In this process dialysis of colloidal solution is carried under the effect of electric field. Some potential is applied between the metal screens that support the membranes. Due to this potential, the speed of the ions moving in the direction of opposite electrodes is increased. Thus the rate of dialysis is increased. This method is not useful for the non-electrolyte impurities like urea etc.
If filter paper is made with the colloidal or some regenerated cellulose like cellophane, the size of the pores is decreased. This modified form of filter paper is known as ultrafilter. The process in which the particles of the solution are removed out from the liquid medium by electrolysis and by using this ultrafilter is known as ultrafiltration. It is a slow process. To speed up the process some external gas pressure has to be applied.
This method can be useful for the purification as well as for the concentration of the sol. When this process is carried without stirring the solution, then the bottom layer settles down while the top layer consists of pure and concentrated colloids, which can be decantated.
This was just a brief layout of some of the methods of purification of the colloidal solution. To know more in detail about the purification of suspension and colloids and surface chemistry, please visit BYJU’S.