Ion Exchange

Various membrane materials, both natural and synthetic, have the ability to selectively allow or retard passage of charged and uncharged molecules through their surface. These semipermeable membranes are extremely important in ion transport within living systems and have many industrial applications.

The balance between sodium ion, Na⁺, and potassium ion, K⁺, within the cells of living organisms is essential for life. The transport of these ions across the cell membrane allows this proper balance to be maintained.

Semipermeable membranes are used in the purification of large organic molecules. They allow small ionic compounds to pass through, separating them from the larger molecules. This procedure, known as dialysis, is the principle upon which patients with nonfunctioning kidneys can remove harmful waste products artificially.

Commercially, the forced separation of ions from seawater by passing them through a semipermeable membrane is an economical means of transforming sea-water into potable water (water safe for drinking). This technique is known as reverse osmosis and is in use by countries bordering oceans or seas to obtain fresh drinking water.