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Ion Sorption by Soil Separates and Exchange Equilibria Involving Sodium, Potassium, and Rubidium
Author(s) -
Roux F. H.,
Coleman N. T.
Publication year - 1963
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1963.03615995002700060016x
Subject(s) - sorption , vermiculite , chemistry , rubidium , potassium , ion exchange , cation exchange capacity , sodium , soil water , desorption , inorganic chemistry , silt , saturation (graph theory) , mineralogy , ion , adsorption , soil science , geology , organic chemistry , paleontology , mathematics , combinatorics
Sodium‐potassium exchange reactions were studied with four California soils, utilizing chromatographic and equilibrium procedures. Apparent exchange constants varied with ion saturation and indicated a larger affinity for potassium as its equivalent fraction on exchange sites decreased. This was especially true for soils containing biotite‐hydrobiotite‐vermiculite in the coarse fractions. Clay and silt‐size materials from such a soil were packed into columns, and the sorption‐desorption behavior of rubidium was measured using the radioisotope Rb 86 . Irreversible sorption of rubidium with corresponding reductions in cation‐exchange capacity was large for silt, intermediate for coarse clay, and negligible for fine clay. Sodium‐rubidium exchange isotherms obtained for various size fractions both before and after a portion of the exchange‐capacity was “blocked” with Rb or K indicated a quite specific sorption of Rb on certain sites, with “normal” ion‐exchange behavior for the remainder of the CEC. X‐ray diffraction studies suggested specific sorption of K and Rb by vermiculite and hydrobiotite, irrespective of the Na/K or Na/Rb ratio in saturating solutions. However, even when sites with specific affinity for Rb or K were eliminated, there was significant variation in the apparent exchange constants obtained for different soils. For soil containing vermiculite in the coarse fractions, the specific sorption of radiorubidium may be a conveniently determined guide to potassium fertilizer needs.