SURFACE MODIFICATION OF CLAY-MINERALS BY ORGANIC POLYIONS

Parallel studies were made of the solid/gas and solid/liquid interfaci al properties and the colloidal behaviour of aqueous dispersions of tw o types of material: soil mineral grains which had been coated with na tural organic matter (humus) and clay minerals (montmorillonite and ka olinite) whose surfaces had been modified synthetically with an organi c polyacid, as models for organo-mineral complexes. Solid samples with and without a polyionic organic coating, and also their aqueous suspe nsions, were investigated by means of nitrogen gas adsorption, small-a ngle X-ray scattering, potentiometric acid-base titration and rheologi cal methods. The organic coating was found to exist as a rough layer o n the surface of the mineral grains, and to plug their pores. Both the natural and the synthetic surface modification resulted in steric and electrostatic stabilization of the clay particles, because of the hig hly charged, polyionic character of the surface-modifying organic matt er. (C) 1998 Elsevier Science B.V. All rights reserved.