This section is a brief discussion of the process reverse osmosis. In this process, liquids or gases are separated from solid or liquid impurities. More specifically to this discussio, salts are removed from water.It was not believed that salt could be removed by a filter because the solutionis in the same phase. Experiments in the 1920's and 30's gave way to small filtration effects in very dilute solutions with colloidal membranes.
As referenced in the history, during the 1950's, the problems of desalting were strongly dealt with. The process of reverse osmosis was designed using special synthetic membranes to separate solutions with even a high concentration of salt. A semipermeable membrane separates a solution from a pure solvent or twosolutions of different concentrations. This is done by a reverse osmotic flow.Actual osmosis is the movement of the phase richer in solvent from the higher concentration to the lesser one. Pressure is put on the system in the opposite direction to the natural flow of osmosis. When the flow reaches the point where it does not move it is called equilibrium pressure. The osmotic presssure is the equilibrium pressure difference between the solvent and solution phases. If the pressure is increased from this point then the flow is in the reverse direction. This is the basis for reverse-osmosis desalination.
This process does have limiting factors such as the high cost to acquire the pressures needed to reverse the flow. There are a few types of membranes that are more effecient than others and these also have a high cost.