dialysis

dialysis

1. the separation of small molecules from large molecules and colloids in a solution by the selective diffusion of the small molecules through a semipermeable membrane

2. Med See haemodialysis peritoneal dialysis

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

dialysis

[dī′al·ə·səs]

(physical chemistry)

A process of selective diffusion through a membrane; usually used to separate low-molecular-weight solutes which diffuse through the membrane from the colloidal and high-molecular-weight solutes which do not.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Dialysis

 

the removal of impurities of low-molecular-weight substances from colloidal systems and solutions of macromolecular compounds by means of semipermeable membranes, or partitions, which pass small molecules and ions but hold back colloidal particles and macromolecules.

The simplest device for dialysis, a dialyzer, is a pouch or sleeve made of semipermeable material that is filled with the liquid to be purified and immersed in a solvent (a dispersion medium). Cylindrical vessels with a semipermeable membrane instead of a bottom are often used in place of a pouch. The membranes are made of collodion, cellophane, animal and plant membranes, and synthetic materials. Diffusion processes are the basis of dialysis; therefore, it proceeds very slowly. Dialysis may be accelerated by increasing the ratio of the membrane area to the volume of the liquid to be dialyzed, by increasing the temperature, by agitation, by creating a pressure difference across the membrane, and by frequent or continuous replacement of the solvent into which the ions or molecules of the low-molecular-weight substance pass (diffuse) through the membrane.

Dialysis in an electric field (electrodialysis) accelerates the removal of electrolytes from dialyzed systems by dozens of times. A simple electrodialyzer consists of three chambers separated by membranes. The liquid to be purified is poured into the central chamber, and electrodes immersed in solvent are located in the side flow chambers. The ions in the stationary electrical field move directly to the corresponding electrodes, penetrating the membrane from the central chamber into the side chambers. Electrodialysis is particularly efficient when ionite membranes made of ion-exchange materials are used. Depending on the sign of the electrical charge on their surface, the membranes pass either cations or anions. Multichamber electrodialyzers with ionite membranes are used in hydrometallurgy, in the atomic industry (to treat effluents, concentrate saline solutions, and separate elements close in properties), and in the desalinization of seawater.

Dialysis and electrodialysis are used in many industrial processes, in physicochemical and biological research, and in medicine. The dialysis method, which was called vivi-diffusion, was used in 1913 by the American scientist D. Abel to study the components of the blood of a living organism. The animal’s blood passed from an artery into a vein through colloidal tubes placed in a glass cylinder filled with physiologic solution. Abel’s unit was the basis for the design of the artificial kidney, which is used for hemodialysis.

REFERENCES

Voiutskii, S. S. Kurs kolloidnoi khimii. Moscow, 1964.
Elektrokineticheskie svoistva kapilliarnykh sistem. Moscow-Leningrad, 1956.
Perry, J. H. Spravochnik inzhenera-khimika, vol. 1. Leningrad, 1969. Page 624. (Translated from English.)
Demineralizatsiia metodom elektrodializa (ionitovye membrany). Moscow, 1963. (Translated from English.)

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.