Kinetic and Equilibrium Studies of Boron Desorption from Soil

Abstract

Abstract Kinetics of boron desorption from soil were determined using 0.05 M mannitol solutions to create pseudo first‐order reaction conditions. The results showed two separate pseudo first‐order reactions and one very slow reaction for which detailed kinetic treatment was not attempted. The relative amount of boron associated with the two fast reactions was independent of soil texture and of initial sample boron content. It was postulated that the two reaction rates were due to desorption from two independent boron retention sites. It was speculated that the two fast reactions were due to desorption from hydroxy iron, magnesium, and aluminum materials in the clay fraction. The third or slowest reaction rate was probably due to diffusion of boron from the interior of clay minerals to solution phase. Equilibrium studies showed that boron desorption followed a 2‐site analog of a linear form of the 1‐site Langmuir expression. Langmuir adsorption maximum values for each site corroborated those calculated from the kinetic study and supported the multisite interpretation of the kinetic data.