Potassium‐aluminium Exchange in Acid Soils I. Kinetics

Abstract

A kinetic method is described and investigated for determining exchangeable A1 in acid soils using M NH,Cl solutions the pH and leaching rate of which was critical for obtaining accurate and reproducible values. Molar concentrations of ammonium acetate displaced at least part of the A1 chelated to functional groups in the soil organic matter.The adsorption kinetics of K and A1 from I O -~ M chloride solutions on the NH,-saturated forms at the original soil pH of these, under leaching conditions similar to the 'extraction' method, showed that, when the atom ratio K/A1 > I in the equilibrating solution, initially more K was adsorbed than at equilibrium, although A1 did not 'over-equilibrate' when K/AI < I. At least 24 h were required for attaining equilibrium in K:AI equilibria work with soils and clays.The kinetics of desorption (extraction method) and adsorption of K and A1 obeyed the first-order and parabolic rate respectively. This is attributed to the large difference in anion concentrations in the two methods.

Potassium Dynamics in Soils

“…A number of researchers have successfully used a simple first-order equation to describe K exchange on clay minerals and soils (Sivasubramaniam and Talibudeen, 1972;Sparks et al, 1980b;Sparks and Jardine, 1981;Jardine and Sparks, 1984a;Sparks and Jardine, 1984); nonexchangeable K release from soils (Burns and Barber, 1961;Martin and Sparks, 1983;Sadusky and Sparks, 1985); and K release from K-bearing minerals (Mortland, 1958;Mortland and Ellis, 1959;Mortland, 1961;Reed and Scott, 1962;Huang et al, 1968;Scott, 1968;Feigenbaum and Shainberg, 1975;Mirecki et al, 1985). The final forms of first-order equations to describe K adsorption and desorption processes using batch and miscible displacement techniques are given in Table 7.…”

“…Numerous researchers have used the parabolic diffusion law to describe K dynamics in soils and clay minerals (Rausell-Colom et al, 1965;Chute and Quirk, 1967;Quirk and Chute, 1968;Sivasubramaniam and Talibudeen, 1972;Sparks et al, 1980c;Feigenbaum et al, 1981;Jardine and Sparks, 1984a;Sparks and Jardine, 1984;. Sivasubramaniam and Talibudeen (1972) working on AI-K exchange on British soils, obtained parabolic plots that gave two distinct slopes, which the authors theorized could be indicative of two simultaneous diffusion-controlled reactions.…”

“…Sivasubramaniam and Talibudeen (1972) working on AI-K exchange on British soils, obtained parabolic plots that gave two distinct slopes, which the authors theorized could be indicative of two simultaneous diffusion-controlled reactions. The authors speculated that the rate-controlling step in the adsorption of A 13+ and K + ions was the diffusion of the ions into the subsurface layers of the solid.…”

“…The reaction rate between soil solution and exchangeable phases of K is strongly dependent on the type of clay minerals present (Sivasubramaniam and Talibudeen, 1972;Sparks, 1980;Sparks et al, 1980b,c;Jardine, 1981, 1984;Sparks and Rcchcigl, 1982;Jardine and Sparks, 1984a) and the method employed to measure the kinetics of K exchange (Sparks and Rechcigl, 1982;Sparks, 1985a,b;Sparks and Huang, 1985;Ogwada and Sparks, 1986a,b). Vermiculite, montmorillonite, kaolinite, and hydrous mica vary drastically in their ionic preferences, ion-binding affinities, and types of ion-exchange reactions.…”

“…Flow or miscible displacement techniques have been used to a lesser extent to investigate the dynamics of K reactions in clay minerals and soils (Sivasubramaniam and Talibudeen, 1972;Sparks et al, 1980c;Sparks and Jardine, 1981;Jardine and Sparks, 1984a;Sparks, 1985a,b). However, flow techniques may be preferable to batch studies in examining K sorptiondesorption phenomena on colloids, particularly if one wishes to relate kinetic studies to solute transport under field conditions Aylmore, 1981, 1983a,b).…”