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

Northwest Agricultural Univ., People's Republic of China

Philip F. Low^*

Agronomy Dep., Purdue Univ., West Lafayette, IN 47907

*Corresponding author.

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 , the extrapolated shear stress, and _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.

Contribution from the Dep. of Agronomy, Purdue Univ. Agric. Exp. Stn. Journal Paper no. 12395.

Received for publication February 26, 1990.

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