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Phosphate Desorption from Kaolinite Suspensions
Author(s) -
BarYosef B.,
Kafkafi U.
Publication year - 1978
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/sssaj1978.03615995004200040007x
Subject(s) - kaolinite , desorption , dilution , chemistry , suspension (topology) , dissolution , activation energy , electrolyte , dissolved silica , leaching (pedology) , phosphate , chromatography , inorganic chemistry , mineralogy , adsorption , soil water , organic chemistry , geology , physics , mathematics , electrode , homotopy , soil science , pure mathematics , thermodynamics
Phosphate desorption from soil minerals is one of the factors which determine the rate of P uptake by plants. Under laboratory conditions desorption is usually obtained by drastic dilution or leaching of the clay, thus inducing its dissolution. The objective of this work was to study the effect of the desorption method used, equilibration time and the dissolved silica on the desorption of P from kaolinite. Two desorption methods were used: (i) diluting 1% suspensions by various volumes of the same electrolyte, and (ii) immersing a dialysis tube containing 0.25% suspension (+P) in an identical suspension initially free of P. The desorption process in both cases could be divided into a rapid and a slow first‐order reaction. The rapid reaction rate constant was similar in both systems (about 4.65 × 10 −3 hours −1 at 25°C). The slow reaction constants were 0.3 × 10 −3 hours −1 and 1.15 × 10 −3 hours −1 for cases (i) and (ii), respectively. The activation energy of the desorption process in case (ii) was 16.2 Kcal/mole for the rapid and 4.8 Kcal/mole for the slow reaction. The amount of silica dissolved from kaolinite due to dilution with 0.01 M KCl depended on the dilution ratio and reached 16 mg SiO 2 /g kaolinite when the suspension was diluted 100‐fold. Readsorption of part of the dissolved silica is stipulated to contribute to the fast P desorption process.