Effect of Sodium‐Humate on the Rheological Characteristics of Montmorillonite Suspensions

Abstract

Abstract Humic compounds are supposed to have an aggregating effect on soil particles. This study was conducted to determine whether Na‐humate aggregates montmorillonite, a common clay mineral. A rotational viscometer was used to investigate the rheological behavior of suspensions of Na‐montmorillonite containing different concentrations of Na‐humate. Thereafter, the pan of an electrobalance was submerged at a given depth in each suspension and the particle‐size distribution of the montmorillonite was determined by continually weighing the sediment that accumulated on the pan. The effect of Na‐humate on swelling of the clay was also investigated by means of a miniature pressure membrane apparatus and by an x‐ray diffractometer. It was found that θ, the extrapolated shear stress, and η pl , the plastic viscosity of the suspensions, decreased rapidly with Na‐humate concentration up to 0.1% (w/w) and then remained nearly constant. However, there was essentially no change in the particlesize distribution and swelling of the clay. These results were interpreted to mean that, in a suspension of montmorillonite and Na‐humate, the humic polyanions absorb on the edges of the particles and, as a result, reduce the attractive force between them. This implies that the aggregating effect of organic matter on soils cannot be attributed to the Na‐humate present in the organic matter.