Abstract <p>The pseudo-first and pseudo-second order equations used to describe the kinetics of adsorption in solutions are considered. It is shown that they are mainly empirical approximating equations. Based on the mathematical analogy with adsorption isotherms, new expressions for approximating kinetic adsorption curves are proposed. Molecular kinetic analysis of monomolecular adsorption in solutions was performed. A new model of this process has been obtained, taking into account the influence of temperature, hydrodynamics, and other factors on its kinetics. As a consequence, the proposed model yields the Langmuir equation and a number of expressions that allow one to calculate the value of equilibrium adsorption, as well as to estimate the parameters of the adsorption process based on data on its kinetics. It is shown that the integral form of the pseudo-second order equation is also a consequence of the proposed molecular kinetic model. A comparison was made with experimental data on the kinetics of adsorption in solutions published in the literature.</p>