An explanation for rheological properties of montmorillonite at low electrolyte concentrations and assessment of irrigation practices in northwestern Indiana

Jin-Song Chen, Purdue University

Abstract

To investigate whether or not positive edge-negative face attraction accounts for the rheological behavior of montmorillonite suspensions at low electrolyte concentration, 0.2, 0.5, 0.6 and 2% w/w suspensions of Na-montmorillonite were prepared at different NaCl concentrations at pH 4, 7 or 10 for the measurement of the extrapolated shear stress, $\theta$, the plastic viscosity, $\eta$, and the absorbance, A. It was found that $\theta$ and $\eta$ were highly correlated. Both fell to a minimum and rose thereafter with increasing NaCl concentration. Also, it was found that A remained constant until the NaCl concentration reached a value corresponding to that at the minimum in $\theta$. Thereafter, it began to increase and became linearly related to $\theta$. Study on the Mg$\sp{2+}$ released from Na-montmorillonite showed: (i) that it decreased by increasing NaCl concentration to a minimum and increasing thereafter, (ii) that Mg$\sp{2+}$ release and $\theta$ were positively correlated and (iii) that three different reactions were involved. It was concluded that: (1) positive edge-negative face interaction cannot account for the rheological properties of montmorillonite at low electrolyte concentration, and (2) the Mg$\sp{2+}$ release from the montmorillonite affects $\theta$ because it reduces the electronegativity of the particles and, thereby, the repulsive force between them. A case study was conducted in Newton and Jasper Counties, Indiana to assess irrigation practices of pumping water from the bedrock aquifer which was separated from the phreatic aquifer by an aquitard of variable thickness. From 1985 to 1987, piezometric surface, water table, ditch water levels, rainfall, soil moisture and corn root growth were monitored. Results of spectral analysis showed: (1) Where the aquitard existed, the water table of the surficial aquifer was not measurably affected by bedrock pumpage and its was slightly affected when the aquitard was absent or thin. The water table and soil moisture were affected by evapotranspiration and rainfall. (2) A minor amount of deep aquifer mining was observed. (3) Plant root growth was unaffected by bedrock pumpage. A model was constructed to predict piezometric surface using current pumping records and previous years piezometric surface maps.

Degree

Ph.D.

Advisors

Cushman, Purdue University.

Subject Area

Agronomy

COinS