Estimation of the electric double layer thickness in the presence of two types of ions in soil water

Abstract The deficit of charges on the clay surface is balanced by the cations in soil water forming the electric double layer (EDL). In sodic soil monovalent Na + ions are dominant and hence, thickness of the EDL ( β ) is more than in the nonsodic soil where bivalent Ca 2 + ions are dominant. For reclaiming the sodic soil, gypsum is added as a source of Ca 2 + ions to replace the Na + ions from the EDL as well as for reducing β . In this paper, an analytical solution is derived to the nonlinear Poisson–Boltzman equation and the solution is used for computing β exactly. A comparison is made between β computed from the solutions of linearized and nonlinear Poisson–Boltzman equation. The solution to the linearized Poisson–Boltzman equation overestimates β . Therefore, it is appropriate to adopt the solution of the nonlinear Poisson–Boltzman equation for computing β .