Colloid movement through stable soils of low cation-exchange capacity

Abstract

Factors controlling the transport of mobile colloids through soils are poorly understood yet have major environmental impacts. This study attempted to identify the relative significance of two physical factors controlling movement of different illitic clays through columns of various stable, nonreactive soils: (i) pore size distribution of the soil matrix and (ii) average size of mobile colloids. The columns were leached with various clay suspensions, and colloid concentrations were measured in relation to effluent solution chemistry. No single factor dominated colloid mobility through the soils tested: pore size distribution exerted some control, but so too did size of the mobile colloids (partly affected by cation status). The most mobile colloids in low-charge soils may simply be fine enough to escape physical filtration by the soil matrix. This applies mainly to near-saturated soils, because as soils dry, greater salt concentrations and particle interactions increase mobile-particle sizes and thus increase the degree of possible physical filtration.