The paper investigates the diffusion of Na ⁺ and Cl ⁻ in a pore liquid between illite microparticles using the quantum-chemical modeling in Materials Studio. The potential distribution induced by the surface charge of the clay mineral layer, disturbs the uniform distribution of cations and anions observed in the bulk solution. As a result, a layer of immobile cations appears near the microparticle surface. As the distance from the surface grows, the anion concentration grows also, while the potential decreases down to zero. In the appeared double-electric layer, the cation diffusion conditions differ. The particle migration rate in the outer surface of the illite microparticle decreases sequentially for water, anion, cation.