ADSORPTION OF POLYACRYLAMIDE AND POLYSACCHARIDE POLYMERS ON SOIL MATERIALS

Knowledge of adsorptive behavior of polymers is useful in predicting their mobility in soil, depth of effective treatment, and other factors related to soil physical conditions. Adsorption isotherms were determined by batch technique for six tritium labeled polymers on three soils, one of which was pretreated to create a high exchangeable sodium percentage (ESP) of 34, and on washed quartz sand of three size fractions. The three anionic polyacrylamide (PAM) compounds had negative charge density of 40J > 21J > 2J, and the three polysaccharide compounds (guar) had a higher positive charge (T-4141), a lower positive charge (CP-14), and a negative charge (T-4246). Adsorption of CP-14, 21J, and T-4246 was measured on montmorillonitic clay extracted from one soil and a specimen sample of montmorillonite clay. Adsorption of a given polymer on the low ESP soils was not significantly different, but was significantly higher on the high ESP soil. The adsorption isotherms were T-4141 greater-than-or-equal-to 21J > CP-14 >> 40J greater-than-or-equal-to 2J > T-4246, and adsorption on sand was only a little less than on soil. The adsorption on clay was CP-14 >> T-4246 > 21J. The data suggest that the PAM and guar polymers studied do not penetrate the aggregates, because adsorption was approximately the same for all soils of similar aggregate sizes. Molecular size, molecular conformation, and electrostatic charge each significantly affected the adsorption isotherms.