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The effect of time on the competition between anions for sorption
Author(s) -
BARROW N. J.
Publication year - 1992
Publication title -
journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 0022-4588
DOI - 10.1111/j.1365-2389.1992.tb00148.x
Subject(s) - sorption , phosphate , penetration (warfare) , selenium , adsorption , competition (biology) , chemistry , environmental chemistry , ecology , organic chemistry , mathematics , biology , operations research
SUMMARY Solutions of phosphate and of selenite were gently mixed with a soil, both separately and in combination, for periods ranging from 15 min to 30 days. For both anions, the solution concentration continued to decrease throughout the period, but the decrease was more marked for phosphate. Competitive effects were smallest after brief periods of mixing, and increased with time. Phosphate was a more effective competitor for sorption than selenite, and its competitive advantage increased with time. The observed effects were closely described by a mechanistic model. According to the model, competition was largely through changes in the electric potential of the surface rather than through decreases in the number of vacant adsorption sites. This explained why competition effects were initially small. This was especially so for phosphate, which was modelled as having a marked continuing diffusive penetration of the surface. The decrease in electric potential associated with that penetration decreased the surface concentration of selenite and so decreased the rate of penetration of selenite. By the end of the experiment this was the most important aspect of the competitive effect of phosphate on selenite.