Alteration in the Surface Properties of Soils by Ion Exchange Resins

Abstract

WHEN soils suspended in glass-distilled water were labelled with phosphorus-32, the rapidly exchanging fraction of the isotopically labile phosphate reacted during the first 10 hr. according to a first-order mechanism, either by ‘film’ diffusion or by ‘mass action’. Suspensions of the soils with mixed resins (Na⁺ : ‘Zeokarb 225’, and Cl⁻ : ‘Amberlite IRA 401’) behaved quite differently. The rate at which this fraction of the soil phosphate was exchanged by chloride ions from the strongly dissociating resin exchanger was governed by ‘bulk’ or ‘intra-particle’ diffusion during 4 days. The mixed resins removed little or none of the remaining ‘slowly’ exchangeable part of the isotopically labile soil phosphate. (In the absence of resins, this ‘slow’ fraction exchanged isotopically according to a single ‘bulk’ diffusion mechanism.) Phosphate diffusion within the resin particle was not the factor controlling the rate of exchange in mixed suspensions of soil and resin because exchange equilibrium was reached in less than 15 min. with Cl : ‘Amberlite IRA 401’ alone in phosphate solutions.