Sorption

sorption [′sȯrp·shən]

(physical chemistry)

A general term used to encompass the processes of adsorption, absorption, desorption, ion exchange, ion exclusion, ion retardation, chemisorption, and dialysis.

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Sorption 

the removal of a substance from the surrounding medium by a solid or liquid. The solid or liquid is called the sorbent, and the substance removed, the sórbate. A distinction is made between removal by the entire mass of a liquid sorbet (absorption) and removal by the surface layer of a solid or liquid sorbent (adsorption). The removal of a substance from a gaseous medium by the entire mass of a solid or melt is also referred to as occlusion. Sorption that is accompanied by a chemical reaction between the sorbent and sórbate is called chemisorption. Capillary condensation frequently occurs during the sorption of vapors by highly porous bodies. The various types of sorption usually occur simultaneously in sorption processes.

Sorption is very important in biological systems, as seen in the sorption (adsorption) of certain substances on the surfaces of cells and on the membranes of intracellular structures and in the sorption (absorption) by cell organoids and biopolymer molecules. High selectivity in sorption, brought about by features in the spatial configuration of sorbent molecules, is characteristic of biological systems. These macromolecules act as receptors for the corresponding sórbate. Examples of sorption can be seen in the binding of CO₂ molecules by chloroplasts during plant photosynthesis, the binding of amino acids by erythrocytes, which transport the acids to tissue cells, and the attachment of a bacteriophage to the surface of a bacterial cell in the host range.

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Sorption 

in hydrometallurgy, the physicochemical process for the removal of valuable components (simple or complex ions of various elements) from solutions or slurries by solid or liquid sorbents during the leaching of ores and concentrates. Synthetic ion-exchange sorbents (cation- and anion-exchange sorbents, ampholytes, complexing agents) are widely used for the sorption of, among other elements, uranium, gold, and molybdenum. The combined leaching and sorption from slurries (sorption leaching) increases the capacity of the process for treating ores and eliminates such time-consuming operations as separation of the solid and liquid phases (filtration, reflux decantation), precipitation, and dissolution.

The separation of the sorbent from the slurry may be achieved on a septum, in a rising stream, by flotation, and by magnetic separation. Sorption processes are used to obtain compounds of high purity and to separate elements with similar physical and chemical properties (rare-earth elements, platinum group of metals, transuranium elements). In the production of zinc, copper, and nickel, sorption methods are used to remove impurities from the solutions before electrolysis, thereby allowing the production of metals of high purity and the extraction of certain associated metals. Processes based on sorption are used with good results in flow processes to prevent the discharge of toxic wastes into the surrounding environment; they are also used for the extraction of metals from waste, mine, and natural waters and for the absorption of harmful gases and vapors that are often liberated during the treatment of various ores and concentrates. The use of sorption processes is now contemplated for extracting uranium and other valuable elements from seawater and for separating isotopes.

REFERENCES

Inoobmennaia tekhnologiia (collection of articles). Moscow, 1959. (Translated from English.)
Plaksin, I. N., and S. A. Tetaru. Gidrometallurgiia s primeneniem ionitov. Moscow, 1964.
lonnyi obmen i ionity (collection of articles). Leningrad, 1970.
lonity v tsvetnoi metallurgii. Moscow, 1975.

B. N. LASKORIN