Effects of anionic polyacrylamide on the adsorption behavior and physical properties of cohesive soil in the northeastern coast of Brazil

This research examines the impact of anionic polyacrylamide (PAM) on the adsorption dynamics and physical properties of cohesive soils located in the Coastal Tablelands of Pernambuco, Brazil. Cohesive soils, known for their high density and restricted water infiltration, present significant challenges for agricultural productivity. Soil samples from different horizons (A, E, BE, and Bt) were treated with PAM to analyze its adsorption kinetics, isotherms, and its potential to decrease soil cohesion. The adsorption experiments fitted pseudo-first and pseudo-second-order kinetic models, revealing variations in PAM behavior across the soil layers. The Bt horizon demonstrated the highest capacity for adsorption, while the A horizon showed unexpected desorption patterns. For the adsorption isotherm tests, two conditions were evaluated: one with the soil in its natural state and another devoid of cementing agents. The isotherms were analyzed using Langmuir, Freundlich, and Sips models, with the Sips model yielding the best fit for PAM adsorption in both conditions. The study concluded that PAM positively affected soil physical characteristics; however, its adsorption was notably affected by the presence of cementing agents such as Fe, Si, Al, and organic matter. The absence of these agents resulted in decreased adsorption and enhanced PAM mobility within the soil. These results underscore PAM's potential to improve soil structure and alleviate the adverse effects of soil cohesion, thereby promoting better water retention and agricultural productivity in cohesive soils.