Premium
Relation Between Potassium Fixation and the Oxidation State of Octahedral Iron
Author(s) -
Chen S. Z.,
Low P. F.,
Roth C. B.
Publication year - 1987
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/sssaj1987.03615995005100010017x
Subject(s) - chemistry , dithionite , sodium dithionite , potassium , ferrous , sodium , inorganic chemistry , bicarbonate , ferric , clay minerals , nuclear chemistry , mineralogy , biochemistry , organic chemistry , enzyme
Samples of the <2‐µm fractions of five pure smectites and six soil clays were reduced by sodium dithionite in the presence of a potassium citrate‐bicarbonate buffer. Subsequently, they were freed of excess electrolyte by dialyzing them in a deoxygenated, 10 −3 M KCl solution. Subsamples of the resulting clays were used to determine Fe 2+ /total Fe, the ratio of ferrous Fe to total Fe; m w /m c , the mass ratio of water to clay, at a swelling pressure of 0.3 MPa; K T , the total K; K E , the exchangeable potassium; and K F , the fixed K. Identical samples of the same smectites and soil clays were subjected to the same experiments except that they were treated with sodium sulfate instead of sodium dithionite. Hence, they remained in the oxidized state. Then the differences in the experimental results for the reduced and oxidized samples were determined. For the several samples, it was found that ΔK F , the change in K F , was proportional to Δ( m w /m c ), the change in m w /m c . Also, it was found that ΔK F was an exponential function of 1/ΔFe 2+ , where ΔFe 2+ is the change in Fe 2+ , but that the constants in this function were different for the pure smectites than for the soil clays. From these findings it was concluded that K + fixation is enhanced by the reduction of octahedral ferric Fe in the clay crystal and that the difference between the pure smectites and soil clays was attributable to nonsmectite minerals in the latter.